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BackgroundBackground Cannabis is commonlyCannabis is commonly
regarded as aninnocuous drugand theregarded as an innocuous drugand the
prevalence of lifetime and regular usehasprevalence of lifetime and regular usehas
increased in mostdeveloped countries.increased in mostdeveloped countries.
However, accumulative evidenceHowever, accumulative evidence
highlights the risks of dependence andhighlights the risks of dependence and
other adverse effects, particularly amongother adverse effects, particularly among
people with pre-existingpsychiatricpeople with pre-existingpsychiatric
disorders.disorders.
AimsAims To re-evaluate the adverse effectsTo re-evaluate theadverse effects
of cannabis inthe general population andof cannabis inthe general population and
among vulnerable individuals, includingamong vulnerable individuals, including
those with serious psychiatric disorders.those with serious psychiatric disorders.
MethodMethod Awide-ranging reviewoftheAwide-ranging reviewofthe
topics related tothese issues.topics relatedtotheseissues.
Results and conclusionsResults and conclusions AnAn
appreciable proportion of cannabisusersappreciable proportion of cannabisusers
report short-lived adverse effects,report short-lived adverse effects,
includingpsychotic states followingheavyincludingpsychotic states followingheavy
consumption, and regular users are at riskconsumption, and regular users are at risk
of dependence.People with major mentalof dependence.People with major mental
illnesses such as schizophrenia areillnesses such as schizophrenia are
especially vulnerableinthatcannabisespecially vulnerableinthatcannabis
generallyprovokes relapse and aggravatesgenerallyprovokes relapse and aggravates
existing symptoms.Health workers needexisting symptoms.Healthworkers need
to recognise, and respond to, the adverseto recognise, and respondto, the adverse
effects ofcannabis on mentalhealth.effects ofcannabis on mentalhealth.
Declaration of interestDeclaration of interest ThisreviewThis review
was commissioned and funded by thewas commissioned and funded by the
Department of Health, butthe findingsDepartment of Health, butthe findings
are those ofthe author alone.are those ofthe author alone.
UNTOWARD MENTALUNTOWARD MENTAL
EFFECTS OF CANNABISEFFECTS OF CANNABIS
The untoward mental effects of cannabisThe untoward mental effects of cannabis
may be classified:may be classified:
(a)(a) Psychological responses such as panic,Psychological responses such as panic,
anxiety, depression or psychosis.anxiety, depression or psychosis.
These effects may be described asThese effects may be described as
`toxic' in that they generally relate to`toxic' in that they generally relate to
excess consumption of the drug.excess consumption of the drug.
(b)(b) Effects of cannabis on pre-existingEffects of cannabis on pre-existing
mental illness and cannabis as a risk-mental illness and cannabis as a risk-
factor for mental illness.factor for mental illness.
(c)(c) Dependency or withdrawal effects.Dependency or withdrawal effects.
The effects of cannabis on cognition areThe effects of cannabis on cognition are
separately reviewed by Ashton (2001, thisseparately reviewed by Ashton (2001, this
issue).issue).
PSYCHOLOGICALPSYCHOLOGICALRESPONSES TO CANNABISRESPONSES TO CANNABIS
There is good evidence that taking cannabisThere is good evidence that taking cannabis
leads to acute adverse mental effects in aleads to acute adverse mental effects in a
high proportion of regular users. Many ofhigh proportion of regular users. Many of
these effects are dose-related, but adversethese effects are dose-related, but adverse
symptoms may be aggravated by con-symptoms may be aggravated by con-
stitutional factors including youthfulness,stitutional factors including youthfulness,
personality attributes and vulnerability topersonality attributes and vulnerability to
serious mental illness.serious mental illness.
Cannabis and mood changeCannabis and mood change
The acute response to cannabis generallyThe acute response to cannabis generallyincludes euphoria and feelings of detach-includes euphoria and feelings of detach-
ment and relaxation. Adverse effects arement and relaxation. Adverse effects are
not uncommon: these are generally short-not uncommon: these are generally short-
lived, but may persist or recur withlived, but may persist or recur with
continued use of the drug.continued use of the drug.
From New Zealand, a sample of 1000From New Zealand, a sample of 1000
people aged 1825 were asked to completepeople aged 1825 were asked to complete
a self-administered questionnaire ona self-administered questionnaire on
cannabis use and related problemscannabis use and related problems
(Thomas, 1996). Those respondents who(Thomas, 1996). Those respondents who
admitted using cannabis (38%) were askedadmitted using cannabis (38%) were asked
about mental health consequences; of these,about mental health consequences; of these,
22% reported panic attacks or anxiety.22% reported panic attacks or anxiety.Women were twice as likely as men toWomen were twice as likely as men to
report these symptoms. Troisireport these symptoms. Troisi et alet al (1998)(1998)
used urine tests on Italian draftees toused urine tests on Italian draftees to
identify 133 men who used only cannabis.identify 133 men who used only cannabis.
All individuals with a pre-existing psychosisAll individuals with a pre-existing psychosis
or severe personality disorder had beenor severe personality disorder had been
excluded. An adjustment disorder withexcluded. An adjustment disorder with
depressed mood was found in 16%, majordepressed mood was found in 16%, majordepression in 14%, and dysthymia indepression in 14%, and dysthymia in
10.5%. The severity of these symptoms10.5%. The severity of these symptoms
was dose-related. No acute psychoticwas dose-related. No acute psychotic
symptoms were reported. Reillysymptoms were reported. Reilly et al et al
(1998) describe the adverse effects found(1998) describe the adverse effects found
among 268 cannabis users who had takenamong 268 cannabis users who had taken
the drug for at least 10 years, and who con-the drug for at least 10 years, and who con-
tinued to smoke about two refers a day.tinued to smoke about two refers a day.
The most common adverse effects wereThe most common adverse effects were
feelings of anxiety, paranoia or depressionfeelings of anxiety, paranoia or depression
(21%), tiredness and low motivation(21%), tiredness and low motivation
(21%).(21%).
Among individuals making seriousAmong individuals making seriousattempts at suicide, 16.2% met criteria forattempts at suicide, 16.2% met criteria for
cannabis misuse/dependence comparedcannabis misuse/dependence compared
with 1.9% of controls much of the highlywith 1.9% of controls much of the highly
significant association was thought to besignificant association was thought to be
due to independent variables including co-due to independent variables including co-
morbidity, but it is suggested that cannabismorbidity, but it is suggested that cannabis
misuse makes a direct contribution to themisuse makes a direct contribution to the
risk of serious self-harm, either directly orrisk of serious self-harm, either directly or
by aggravation of other mental disordersby aggravation of other mental disorders
(Beautrais(Beautrais et alet al, 1999)., 1999).
Cannabis and psychosisCannabis and psychosisCannabis use can lead to a range of short-Cannabis use can lead to a range of short-
lived symptoms such as depersonalisation,lived symptoms such as depersonalisation,
derealisation, a feeling of loss of control,derealisation, a feeling of loss of control,
fear of dying, irrational panic and para-fear of dying, irrational panic and para-
noid ideas (Thomas, 1993). For example,noid ideas (Thomas, 1993). For example,
Thomas (1996) reported that, amongThomas (1996) reported that, among
cannabis users who responded to his sur-cannabis users who responded to his sur-
vey, 15% identified psychotic symptomsvey, 15% identified psychotic symptoms
such as hearing voices or having un-such as hearing voices or having un-
warranted feelings of persecution or riskwarranted feelings of persecution or risk
of harmof harm from others. Two small case stu-from others. Two small case stu-
dies have reported prolonged depersonal-dies have reported prolonged depersonal-
isation after cessation of cannabis useisation after cessation of cannabis use(Szymanski, 1981; Keshaven & Lishman,(Szymanski, 1981; Keshaven & Lishman,
1986). `Flashbacks' or the subsequent1986). `Flashbacks' or the subsequent
partial re-experience when drug-free ofpartial re-experience when drug-free of
symptoms experienced during intoxicationsymptoms experienced during intoxication
are rarely reported after cannabis useare rarely reported after cannabis use
(Thomas, 1993).(Thomas, 1993).
The casual use of the term `cannabisThe casual use of the term `cannabis
psychosis' in clinical psychiatric practicepsychosis' in clinical psychiatric practice
and in the scientific literature results inand in the scientific literature results in
diagnostic imprecision and research ofdiagnostic imprecision and research of
uncertain validity. Thornicroft (1990) re-uncertain validity. Thornicroft (1990) re-
views the possible associations betweenviews the possible associations between
cannabis use and psychosis and suggestscannabis use and psychosis and suggeststhat common methodological failings are:that common methodological failings are:
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B R I T I S H J O U R N A L O F P S Y C H I A T RYB R I T I S H J O U R N A L O F P S Y C H I A T RY ( 2 0 0 1 ) , 1 7 8 , 1 1 6 ^ 1 2 2( 2 0 0 1 ) , 1 7 8 , 1 1 6 ^ 1 2 2
Psychiatric effects of cannabisPsychiatric effects of cannabis{{
ANDREW JOHNSANDREW JOHNS
{{See editorial, p.9 8, thisissue.See editorial, p.9 8, thisissue.
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P S Y C HI A T R I C E F F E C T S O F C A N N A B I SP S Y C H IA T R I C E F F E C T S O F C A N N A B I S
(a) studies fail to adequately separate or-(a) studies fail to adequately separate or-
ganic from functional psychotic reactionsganic from functional psychotic reactions
to cannabis; (b) they have insufficiently dis-to cannabis; (b) they have insufficiently dis-
criminated between psychotic symptomscriminated between psychotic symptoms
and syndromes of a psychosis; and (c) theyand syndromes of a psychosis; and (c) they
have not balanced the weight of evidencehave not balanced the weight of evidence
for and against the category of cannabisfor and against the category of cannabispsychosis. Although there is good evidencepsychosis. Although there is good evidence
for believing that cannabis use may infor believing that cannabis use may in
certaincertain circumstances contribute tocircumstances contribute to
psychotic disorders, the connections arepsychotic disorders, the connections are
complex.complex.
HallHall et alet al(1994) suggest that the funda-(1994) suggest that the funda-
mental questions are: is there a cannabismental questions are: is there a cannabis
psychosis, and does cannabis precipitatepsychosis, and does cannabis precipitate
an underlying psychosis? In theory, canna-an underlying psychosis? In theory, canna-
bis use may precipitate a psychosis in thebis use may precipitate a psychosis in the
following ways.following ways.
(a)(a) Acute use of large doses of the drugAcute use of large doses of the drug
may induce a toxic or organic psychosismay induce a toxic or organic psychosis
with symptoms of confusion and hallu-with symptoms of confusion and hallu-
cination, which remit on abstinence.cination, which remit on abstinence.
(b)(b) Cannabis use may lead to an acuteCannabis use may lead to an acute
functional psychosis, similar to anfunctional psychosis, similar to an
acute schizophreniform state andacute schizophreniform state and
lacking the organic features of a toxiclacking the organic features of a toxic
psychosis.psychosis.
(c)(c) Cannabis use may lead to a chronicCannabis use may lead to a chronic
psychosis, which persists after absti-psychosis, which persists after absti-
nence.nence.
(d)(d) Long-term cannabis use may lead to anLong-term cannabis use may lead to an
organic psychosis which only partiallyorganic psychosis which only partiallyremits after abstinence, leaving aremits after abstinence, leaving a
residual deficit state, sometimes calledresidual deficit state, sometimes called
an amotivational syndrome, which isan amotivational syndrome, which is
thought to be analogous to the chronicthought to be analogous to the chronic
organic brain syndrome seen afterorganic brain syndrome seen after
prolonged misuse of alcohol.prolonged misuse of alcohol.
(e)(e) Cannabis use may be a risk-factorCannabis use may be a risk-factor
for serious mental illness such asfor serious mental illness such as
schizophrenia.schizophrenia.
Cannabis and toxic psychosisCannabis and toxic psychosis
Apart from single-case reports, the natureApart from single-case reports, the nature
of cannabis-induced toxic psychosis isof cannabis-induced toxic psychosis isconsidered in the following studies, all ofconsidered in the following studies, all of
which are weakened by the lack of urine-which are weakened by the lack of urine-
testing to confirm the presence of cannabistesting to confirm the presence of cannabis
and the absence of other drugs of misuse.and the absence of other drugs of misuse.
Talbott & Teague (1969) described 12Talbott & Teague (1969) described 12
soldiers in Vietnam who, after their firstsoldiers in Vietnam who, after their first
admitted use of cannabis, showed dis-admitted use of cannabis, showed dis-
orientation, impaired memory, confusion,orientation, impaired memory, confusion,
reduced attention span and disorderedreduced attention span and disordered
thinking with labile effect and hallu-thinking with labile effect and hallu-
cinations. These symptoms resolved withincinations. These symptoms resolved within
a week. Tennant & Groesbeck (1972)a week. Tennant & Groesbeck (1972)
describe psychoses among 36000 USdescribe psychoses among 36000 USservicemen stationed in Germany. Of theservicemen stationed in Germany. Of the
5120 soldiers using cannabis at least three5120 soldiers using cannabis at least three
timestimes a week, 720 presented witha week, 720 presented with
cannabis-cannabis-related problems. The hashishrelated problems. The hashish
available was potent, containing 510%available was potent, containing 510%
tetrahydrocannabinol (THC). The authorstetrahydrocannabinol (THC). The authors
identified 19 cases of a panic attack oridentified 19 cases of a panic attack or
short-lived toxic psychosis, which appearedshort-lived toxic psychosis, which appearedafter a single high dose of hashish, and aafter a single high dose of hashish, and a
further 85 cases of toxic psychosis whichfurther 85 cases of toxic psychosis which
appeared after the consumption of cannabisappeared after the consumption of cannabis
with other drugs. These acute states tendedwith other drugs. These acute states tended
to resolve within 3 days.to resolve within 3 days.
From Calcutta, Chopra & Smith (1974)From Calcutta, Chopra & Smith (1974)
retrospectively identified 200 in-patientsretrospectively identified 200 in-patients
who showed serious psychiatric symptomswho showed serious psychiatric symptoms
after taking cannabis. The most commonafter taking cannabis. The most common
symptoms in all patients were suddensymptoms in all patients were sudden
onset of confusion, often associated withonset of confusion, often associated with
hallucinations and emotional lability.hallucinations and emotional lability.
Disorientation, depersonalisation andDisorientation, depersonalisation andparanoid symptoms were common. Manyparanoid symptoms were common. Many
patients had taken a large dose of cannabis,patients had taken a large dose of cannabis,
which was followed by an intoxicated statewhich was followed by an intoxicated state
for which they were subsequently amnesic.for which they were subsequently amnesic.
Among the 34% of patients without aAmong the 34% of patients without a
previous history of psychiatric disorder,previous history of psychiatric disorder,
adverse symptoms lasted no more than aadverse symptoms lasted no more than a
few days, followed by full recovery. A pre-few days, followed by full recovery. A pre-
vious history of schizophrenia or person-vious history of schizophrenia or person-
ality disorder was associated with longerality disorder was associated with longer
duration of adverse symptoms.duration of adverse symptoms.
From Pakistan, ChaudryFrom Pakistan, Chaudry et alet al (1991)(1991)
report on effects ofreport on effects of bhangbhang, a potent, a potentbeverage made from an infusion of canna-beverage made from an infusion of canna-
bis leaves and flowering tops. They identi-bis leaves and flowering tops. They identi-
fied 15 patients who having takenfied 15 patients who having taken bhangbhang,,
presented with a psychosis with symptomspresented with a psychosis with symptoms
of grandiosity, excitement, hostility, dis-of grandiosity, excitement, hostility, dis-
orientation, hallucinations and thoughtorientation, hallucinations and thought
disorder. Mental state was assessed system-disorder. Mental state was assessed system-
atically, using the Brief Psychiatric Ratingatically, using the Brief Psychiatric Rating
Scale (BPRS) (LukoffScale (BPRS) (Lukoff et alet al, 1986). The, 1986). The
control group of 10 patients all usedcontrol group of 10 patients all used bhangbhang,,
but less frequently than the study group.but less frequently than the study group.
This work suggests that cannabis,This work suggests that cannabis,
especially in high doses, can produce aespecially in high doses, can produce atoxic psychosis in individuals who havetoxic psychosis in individuals who have
no history of severe mental illness. Theno history of severe mental illness. The
main features are mild impairment of con-main features are mild impairment of con-
sciousness, distorted sense of passage ofsciousness, distorted sense of passage of
time, dream-like euphoria, progressing totime, dream-like euphoria, progressing to
fragmented thought processes and halluci-fragmented thought processes and halluci-
nations, generally resolving within a weeknations, generally resolving within a week
of abstinence (Lishman, 1998).of abstinence (Lishman, 1998).
Cannabis and acute functionalCannabis and acute functional
psychosispsychosis
A number of studies suggest that heavyA number of studies suggest that heavycannabis use can lead to an acute functionalcannabis use can lead to an acute functional
illness, that is a state resembling the psy-illness, that is a state resembling the psy-
chosis of acute schizophrenia without thechosis of acute schizophrenia without the
amnesia and confusion of a toxic psychosis.amnesia and confusion of a toxic psychosis.
Tennant & Groesbeck (1972) identifiedTennant & Groesbeck (1972) identified
115 cases of schizophrenic reaction among115 cases of schizophrenic reaction among
the 720 regular users of cannabis; however,the 720 regular users of cannabis; however,
all but three had used cannabis with otherall but three had used cannabis with otherdrugs or alcohol. Thacore & Shukladrugs or alcohol. Thacore & Shukla
(1976) compared 25 individuals with a(1976) compared 25 individuals with a
putative diagnosis of `cannabis psychosisputative diagnosis of `cannabis psychosis
of the paranoid type' with controls diag-of the paranoid type' with controls diag-
nosed with paranoid schizophrenia.nosed with paranoid schizophrenia.
Patients with cannabis psychosis showedPatients with cannabis psychosis showed
more bizarre behaviour, violence, panickymore bizarre behaviour, violence, panicky
affect, more insight and less evidence ofaffect, more insight and less evidence of
thought disorder. They also showed a rapidthought disorder. They also showed a rapid
response to neuroleptics with completeresponse to neuroleptics with complete
recovery. More robust in methodology isrecovery. More robust in methodology is
the work of Rottanburgthe work of Rottanburg et alet al (1982) in(1982) in
which 20 patients with psychosis and withwhich 20 patients with psychosis and withhigh urinary cannabinoids were comparedhigh urinary cannabinoids were compared
with 20 matched cannabis-free controls.with 20 matched cannabis-free controls.
Mental state was assessed using the PresentMental state was assessed using the Present
State Examination (PSE) (WingState Examination (PSE) (Wing et al et al ,,
1974). The cannabis-positive patients had1974). The cannabis-positive patients had
more symptoms of hypomania andmore symptoms of hypomania and
agitation, less auditory hallucinations,agitation, less auditory hallucinations,
flattening of affect, incoherent speech andflattening of affect, incoherent speech and
hysteria than controls. Clouding of con-hysteria than controls. Clouding of con-
sciousness was absent in most cannabissciousness was absent in most cannabis
patients. They also showed markedpatients. They also showed marked
improvements in symptoms within a week,improvements in symptoms within a week,
while the controls remained unwell despitewhile the controls remained unwell despitereceiving comparable antipsychotic drugs.receiving comparable antipsychotic drugs.
The authors conclude that a high intakeThe authors conclude that a high intake
of cannabis may be related to a rapidly re-of cannabis may be related to a rapidly re-
solving psychosis with marked hypomanicsolving psychosis with marked hypomanic
features. However, 16 cannabis-positivefeatures. However, 16 cannabis-positive
psychotic patients left the study pre-psychotic patients left the study pre-
maturely, which may bias the findings onmaturely, which may bias the findings on
the 20 who remained. Rapid resolution ofthe 20 who remained. Rapid resolution of
symptoms is also reported by Carneysymptoms is also reported by Carney et alet al
(1984), who identified nine patients with(1984), who identified nine patients with
cannabis-related psychotic episodes. Theircannabis-related psychotic episodes. Their
differing symptomatology was describeddiffering symptomatology was described
as `schizophreniform, manic, delusionalas `schizophreniform, manic, delusionalpsychosis and confusion'.psychosis and confusion'.
More recently, Mathers & GhodseMore recently, Mathers & Ghodse
(1992) carried out a prospective study of(1992) carried out a prospective study of
in-patients with psychotic symptoms andin-patients with psychotic symptoms and
cannabis-positive urine. Blind to the urinecannabis-positive urine. Blind to the urine
test result, researchers applied the PSE ontest result, researchers applied the PSE on
admission and again at 1 and 6 months.admission and again at 1 and 6 months.
Concurrently admitted patients with psy-Concurrently admitted patients with psy-
chosis but with drug-free urine analysischosis but with drug-free urine analysis
were controls. At 1 week the two groupswere controls. At 1 week the two groups
differed significantly on only five PSEdiffered significantly on only five PSE
items: changed perception, thought inser-items: changed perception, thought inser-
tion, non-verbal auditory hallucinations,tion, non-verbal auditory hallucinations,delusions of control, and delusions ofdelusions of control, and delusions of
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JOHNSJOHNS
grandiose ability; this symptom cluster at 1grandiose ability; this symptom cluster at 1
week was thought to be consistent withweek was thought to be consistent with
acute cannabis intoxication. These differ-acute cannabis intoxication. These differ-
ences were minor at 1 month and absentences were minor at 1 month and absent
at 6 months. Chronic cannabis-inducedat 6 months. Chronic cannabis-induced
psychosis was not found. Caucasianpsychosis was not found. Caucasian
patients were more likely to be depressedpatients were more likely to be depressedwith depersonalisation and derealisation,with depersonalisation and derealisation,
while Africanwhile AfricanCaribbeans showed moreCaribbeans showed more
culturally influenced delusions. However,culturally influenced delusions. However,
these findings could not be replicated bythese findings could not be replicated by
McGuireMcGuire et alet al (1994) who also used the(1994) who also used the
PSE to assess the psychopathology of 23PSE to assess the psychopathology of 23
patients with psychosis who were cannabis-patients with psychosis who were cannabis-
positive on urinary screening, and 46positive on urinary screening, and 46
matched drug-free controls. Cases andmatched drug-free controls. Cases and
controls were indistinguishable in terms ofcontrols were indistinguishable in terms of
psychopathology, DSMIII diagnosespsychopathology, DSMIII diagnoses
(American Psychiatric Association, 1980),(American Psychiatric Association, 1980),
onset of recent illness, the proportion ofonset of recent illness, the proportion offfirst admissions, ethnicity and socio-irst admissions, ethnicity and socio-
economic class, differing only in theireconomic class, differing only in their
histories of substance use.histories of substance use.
Having compared groups of drug-Having compared groups of drug-
misusing patients with psychosis of varyingmisusing patients with psychosis of varying
duration, Tsuangduration, Tsuang et alet al (1982) concluded(1982) concluded
that the shorter-duration disorders werethat the shorter-duration disorders were
drug-induced toxic psychoses, and thedrug-induced toxic psychoses, and the
longer-lasting disorders represented thelonger-lasting disorders represented the
expression of functional psychiatric illnessexpression of functional psychiatric illness
in vulnerable individuals. If corroborated,in vulnerable individuals. If corroborated,
this suggests that the `functional psychosis'this suggests that the `functional psychosis'
related to cannabis use is best explained asrelated to cannabis use is best explained asa precipitated episode of an underlyinga precipitated episode of an underlying
functional illness.functional illness.
Cannabis and chronic psychosisCannabis and chronic psychosis
Ghodse (1986) has suggested that regularGhodse (1986) has suggested that regular
heavy users of cannabis may suffer repeatedheavy users of cannabis may suffer repeated
short episodes of psychosis and effectivelyshort episodes of psychosis and effectively
`maintain' themselves in a chronic psy-`maintain' themselves in a chronic psy-
chotic state. This is a possibility, but Hallchotic state. This is a possibility, but Hall
et alet al(1994) note that it is difficult to distin-(1994) note that it is difficult to distin-
guish between a chronic cannabis psychosisguish between a chronic cannabis psychosis
and the co-occurrence of an illness such asand the co-occurrence of an illness such asschizophrenia with continued cannabisschizophrenia with continued cannabis
use. There is however, no robust evidenceuse. There is however, no robust evidence
that heavy cannabis use may lead to a psy-that heavy cannabis use may lead to a psy-
chotic illness which persists after abstinencechotic illness which persists after abstinence
(Thomas, 1993).(Thomas, 1993).
Cannabis and amotivationalCannabis and amotivational
syndromesyndrome
It has been suggested that heavy cannabisIt has been suggested that heavy cannabis
use could lead to an `amotivational syn-use could lead to an `amotivational syn-
drome' described as personality deterio-drome' described as personality deterio-
rationration with loss of energy and drive towith loss of energy and drive towork (Tennant & Groesbeck, 1972). Thework (Tennant & Groesbeck, 1972). The
supporting evidence largely comprises un-supporting evidence largely comprises un-
controlled studies of long-term cannabiscontrolled studies of long-term cannabis
users in various cultures (Hallusers in various cultures (Hall et al et al ,,
1994). It is probable that amotivational1994). It is probable that amotivational
syndrome represents nothing more thansyndrome represents nothing more than
ongoing intoxication in frequent users ofongoing intoxication in frequent users of
the drug (Negretethe drug (Negrete et alet al, 1986) and the valid-, 1986) and the valid-ity of this diagnosis remains uncertain (Hallity of this diagnosis remains uncertain (Hall
et alet al, 1994)., 1994).
Cannabis as risk-factor for seriousCannabis as risk-factor for serious
mentall illnessmentall illness
Comorbidity ratesComorbidity rates
Cannabis use is associated with high ratesCannabis use is associated with high rates
of comorbidity for other psychiatric diag-of comorbidity for other psychiatric diag-
noses. The Epidemiologic Catchment Areanoses. The Epidemiologic Catchment Area
(ECA) survey (Regier(ECA) survey (Regier et al et al , 1990) of, 1990) of
20000 subjects in community and in-20000 subjects in community and in-
stitutional settings showed that 50.1% ofstitutional settings showed that 50.1% ofindividualsindividuals with cannabis dependence/with cannabis dependence/
misusemisuse also met DSMIII criteria for onealso met DSMIII criteria for one
other non-drug or alcohol mental disorder.other non-drug or alcohol mental disorder.
Among 133 Italian draftees, TroisiAmong 133 Italian draftees, Troisi et alet al
(1998) found that the prevalence of co-(1998) found that the prevalence of co-
morbidity was significantly related to themorbidity was significantly related to the
pattern of cannabis use: 69% of subjectspattern of cannabis use: 69% of subjects
with DSMIIIR cannabis dependence,with DSMIIIR cannabis dependence,
41% of those with cannabis abuse and41% of those with cannabis abuse and
24% of occasional users reported at least24% of occasional users reported at least
one DSMIIIR Axis 1 psychiatric diag-one DSMIIIR Axis 1 psychiatric diag-
nosis. Most common were adjustment dis-nosis. Most common were adjustment dis-
order with depressed mood (order with depressed mood (nn21), major21), majordepression (depression (nn19) and dysthymia (19) and dysthymia (nn14).14).
The severity of symptoms also increasedThe severity of symptoms also increased
with degree of cannabis use. Psychoticwith degree of cannabis use. Psychotic
symptoms were not found, but it shouldsymptoms were not found, but it should
be noted all individuals with psychotic ill-be noted all individuals with psychotic ill-
ness or severe personality disorder wereness or severe personality disorder were
not drafted.not drafted.
There are high rates of drug misuseThere are high rates of drug misuse
among people with mental illness. Theamong people with mental illness. The
ECA study (RegierECA study (Regier et alet al, 1990) showed that, 1990) showed that
the risk of meeting criteria for a substancethe risk of meeting criteria for a substance
misuse disorder was 4.6 times higher inmisuse disorder was 4.6 times higher in
those suffering from schizophrenia than inthose suffering from schizophrenia than inthe general population. Schizophrenia wasthe general population. Schizophrenia was
associated with a six-fold increase in riskassociated with a six-fold increase in risk
of developing a drug use disorder, and can-of developing a drug use disorder, and can-
nabisnabis was the most commonly misusedwas the most commonly misused
drug.drug. MenezesMenezes et alet al (1996) examined the(1996) examined the
prevalence of substance misuse problemsprevalence of substance misuse problems
among 171 patients with psychotic illnessamong 171 patients with psychotic illness
who had any contact with mental healthwho had any contact with mental health
treatment services in a south London area.treatment services in a south London area.
Alcohol problems were more prevalent,Alcohol problems were more prevalent,
but current use of one or more drugs wasbut current use of one or more drugs was
found in 35 subjects (20%); all but two saidfound in 35 subjects (20%); all but two said
they used cannabis. Cantwellthey used cannabis. Cantwell et alet al (1999)(1999)studied 168 subjects presenting with a firststudied 168 subjects presenting with a first
episode of psychosis and found 1-year pre-episode of psychosis and found 1-year pre-
valence rates of 19.5% for drug misuse,valence rates of 19.5% for drug misuse,
11.7% for alcohol misuse, and cannabis11.7% for alcohol misuse, and cannabis
was the most commonly misused substance.was the most commonly misused substance.
Given these findings, it is necessary toGiven these findings, it is necessary to
review the possible role of cannabis as areview the possible role of cannabis as a
risk factor for functional illness and forrisk factor for functional illness and forthe aggravation of symptoms.the aggravation of symptoms.
Effects of cannabis on severe mental illnessEffects of cannabis on severe mental illness
Given that high doses of cannabis can causeGiven that high doses of cannabis can cause
a toxic psychosis, then it may be supposeda toxic psychosis, then it may be supposed
it will aggravate the symptoms of schizo-it will aggravate the symptoms of schizo-
phrenia. However, clinical experience sug-phrenia. However, clinical experience sug-
gests that some patients say that they takegests that some patients say that they take
cannabis as a form of `self-medication'.cannabis as a form of `self-medication'.
For example, DixonFor example, Dixon et alet al (1990) inter-(1990) inter-
viewed 83 patients with schizophrenia orviewed 83 patients with schizophrenia or
schizophreniform psychoses who reportedschizophreniform psychoses who reportedthat cannabis reduced anxiety and depres-that cannabis reduced anxiety and depres-
sion, led to increased suspiciousness andsion, led to increased suspiciousness and
had varied effects on drive and hallucina-had varied effects on drive and hallucina-
tions. Arndttions. Arndt et alet al (1992) investigated a(1992) investigated a
cohort of 131 patients with schizophreniacohort of 131 patients with schizophrenia
and found that previous use of cannabisand found that previous use of cannabis
had no impact on current symptoms.had no impact on current symptoms.
Peralta & Cuesta (1992) reported thatPeralta & Cuesta (1992) reported that
cannabis had no significant effect oncannabis had no significant effect on
positive symptoms of schizophrenia, but itpositive symptoms of schizophrenia, but it
did attenuate negative symptoms.did attenuate negative symptoms.
On the other hand, there are a few con-On the other hand, there are a few con-
trolled studies that have tended to demon-trolled studies that have tended to demon-strate that cannabis aggravates the severitystrate that cannabis aggravates the severity
of positive symptoms. Negreteof positive symptoms. Negrete et alet al (1986)(1986)
described the history of confirmed cannabisdescribed the history of confirmed cannabis
use in 137 patients with schizophrenia inuse in 137 patients with schizophrenia in
treatment. Subjects who were using canna-treatment. Subjects who were using canna-
bis over the 6-month observation periodbis over the 6-month observation period
presented with significantly greaterpresented with significantly greater
delusions and hallucinations, and madedelusions and hallucinations, and made
more use of psychiatric services. Similarly,more use of psychiatric services. Similarly,
CleghornCleghorn et alet al(1991) found that drug-users(1991) found that drug-users
with schizophrenia, among whom cannabiswith schizophrenia, among whom cannabis
was the most heavily used drug, had a high-was the most heavily used drug, had a high-
er prevalence of hallucinations, delusionser prevalence of hallucinations, delusionsand other positive symptoms. This findingand other positive symptoms. This finding
was replicated by Baigentwas replicated by Baigent et alet al (1995),(1995),
who reported that among 53 in-patientswho reported that among 53 in-patients
with a dual diagnosis of substance misusewith a dual diagnosis of substance misuse
and schizophrenia, cannabis was the onlyand schizophrenia, cannabis was the only
drug that worsened positive symptoms.drug that worsened positive symptoms.
Data from the ECA survey (SwansonData from the ECA survey (Swanson
et alet al, 1990) also casts some light on the, 1990) also casts some light on the
possible effects of cannabis use disorderpossible effects of cannabis use disorder
and violence. Subjects were asked aboutand violence. Subjects were asked about
episodes of violence in the previous yearepisodes of violence in the previous year
(i.e. hitting a partner, bruising a child,(i.e. hitting a partner, bruising a child,
fighting, using a weapon in a fight whilefighting, using a weapon in a fight whiledrinking). Of the 191 respondents withdrinking). Of the 191 respondents with
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cannabis abuse or dependence, 19.25%cannabis abuse or dependence, 19.25%
(risk ratio 9.4) had been violent compared(risk ratio 9.4) had been violent compared
with 12.69% (risk ratio 6.2) of those withwith 12.69% (risk ratio 6.2) of those with
schizophrenia or schizophreniform dis-schizophrenia or schizophreniform dis-
order and 24.57% (risk ratio 11.9) oforder and 24.57% (risk ratio 11.9) of
those with alcohol abuse or dependence.those with alcohol abuse or dependence.
Here, the risk is expressed relative to theHere, the risk is expressed relative to the2.05% who were violent among those of2.05% who were violent among those of
the sample population who showed nothe sample population who showed no
psychiatric disorder. However, this doespsychiatric disorder. However, this does
not amount to a causal correlation betweennot amount to a causal correlation between
cannabis co-morbidity and violence, givencannabis co-morbidity and violence, given
the possible role of intervening variablesthe possible role of intervening variables
such as individual and social factors.such as individual and social factors.
That cannabis consumption also has anThat cannabis consumption also has an
adverse effect on the course of schizo-adverse effect on the course of schizo-
phrenia was noted by Negretephrenia was noted by Negrete et alet al (1986)(1986)
and confirmed in a prospective study byand confirmed in a prospective study by
LinszmanLinszman et alet al (1994). A cohort of newly(1994). A cohort of newly
admitted patients with schizophrenia wereadmitted patients with schizophrenia wereassessed monthly for a year, using theassessed monthly for a year, using the
BPRS and self-reports of cannabis use. TheBPRS and self-reports of cannabis use. The
cannabis-using group (cannabis-using group (nn24) experienced24) experienced
significantly more and earlier psychoticsignificantly more and earlier psychotic
relapses and this effect was dose-related.relapses and this effect was dose-related.
As HallAs Hall et alet al(1994) remark, these find-(1994) remark, these find-
ings are a slender basis on which to drawings are a slender basis on which to draw
conclusions about the effect of cannabisconclusions about the effect of cannabis
on schizophrenic symptoms. Until furtheron schizophrenic symptoms. Until further
prospective studies have been carried out,prospective studies have been carried out,
it would be prudent to regard cannabis asit would be prudent to regard cannabis as
a vulnerability factor in relation to majora vulnerability factor in relation to major
mental illness and to caution at-riskmental illness and to caution at-riskindividuals against using the drug.individuals against using the drug.
Cannabis as risk factor for mental illnessCannabis as risk factor for mental illness
There is no evidence that cannabis is a cau-There is no evidence that cannabis is a cau-
sal factor in schizophrenia and it is moresal factor in schizophrenia and it is more
relevant to consider whether the misuse ofrelevant to consider whether the misuse of
the drug constitutes a risk factor for thisthe drug constitutes a risk factor for this
illness. Supporting evidence is found in aillness. Supporting evidence is found in a
prospective study by Andreassonprospective study by Andreasson et al et al
(1987) of 45 570 Swedish conscripts, of(1987) of 45 570 Swedish conscripts, of
whom 9.4% had used cannabis and 1.7%whom 9.4% had used cannabis and 1.7%
were `high consumers' having used morewere `high consumers' having used morethan 50 times. Fifteen-year follow-up datathan 50 times. Fifteen-year follow-up data
were drawn from national registers ofwere drawn from national registers of
deaths and psychiatric cases. Compareddeaths and psychiatric cases. Compared
with non-users, the relative risk of schizo-with non-users, the relative risk of schizo-
phrenia was 2.4 in the group that reportedphrenia was 2.4 in the group that reported
use of cannabis at least once, rising to 6.0use of cannabis at least once, rising to 6.0
among heavy users. Nearly half (430/730)among heavy users. Nearly half (430/730)
of these high consumers had a psychiatricof these high consumers had a psychiatric
diagnosis other than psychosis on conscrip-diagnosis other than psychosis on conscrip-
tion; controlling for this reduced the rela-tion; controlling for this reduced the rela-
tive risk to 2.9. The authors suggest thattive risk to 2.9. The authors suggest that
cannabis consumption is a `life-event stres-cannabis consumption is a `life-event stres-
sor' for individuals vulnerable to schizo-sor' for individuals vulnerable to schizo-phrenia. Hallphrenia. Hall et alet al (1994) offer a number(1994) offer a number
of alternative explanations. There is a largeof alternative explanations. There is a large
temporal gap between self-reported canna-temporal gap between self-reported canna-
bis use on conscription and the develop-bis use on conscription and the develop-
ment of schizophrenia over 15 years, andment of schizophrenia over 15 years, and
no data as to whether the cannabis use con-no data as to whether the cannabis use con-
tinued during this time. Drugs other thantinued during this time. Drugs other than
cannabis could have been taken at any timecannabis could have been taken at any timeafter conscription.after conscription.
It should also be noted that as only 49 ofIt should also be noted that as only 49 of
the 274 conscripts with schizophrenia hadthe 274 conscripts with schizophrenia had
ever tried cannabis, then this drug may onlyever tried cannabis, then this drug may only
be relevant to a minority of cases. Further-be relevant to a minority of cases. Further-
more, Jablenskymore, Jablensky et alet al (1992) demonstrate a(1992) demonstrate a
striking uniformity in the incidence ofstriking uniformity in the incidence of
schizophrenia in cultures with very differentschizophrenia in cultures with very different
rates of cannabis consumption.rates of cannabis consumption.
The possibility of a genetic explanationThe possibility of a genetic explanation
for the association between cannabis usefor the association between cannabis use
and schizophrenia was raised by McGuireand schizophrenia was raised by McGuire
et alet al (1994). In this study, 23 patients with(1994). In this study, 23 patients withpsychosis and with cannabis in their urinepsychosis and with cannabis in their urine
were gender-matched with 46 drug-freewere gender-matched with 46 drug-free
controls with psychosis, and the lifetimecontrols with psychosis, and the lifetime
risk of psychiatric disorder among all therisk of psychiatric disorder among all the
first-degree relatives was ascertained. Thefirst-degree relatives was ascertained. The
cannabis-positive subjects had a signifi-cannabis-positive subjects had a signifi-
cantly greater (7.1%) familial risk ofcantly greater (7.1%) familial risk of
schizophrenia than controls (0.7%),schizophrenia than controls (0.7%),
suggesting that the development or re-suggesting that the development or re-
currence of acute psychosis in the contextcurrence of acute psychosis in the context
of cannabis use may be associated with aof cannabis use may be associated with a
genetic predisposition to schizophrenia.genetic predisposition to schizophrenia.
CANNABIS DEPENDENCECANNABIS DEPENDENCE
Evidence for cannabis dependenceEvidence for cannabis dependence
It had been believed that cannabis use didIt had been believed that cannabis use did
not lead to tolerance and that there wasnot lead to tolerance and that there was
no withdrawal syndrome. However, sinceno withdrawal syndrome. However, since
the mid-1970s, these views have beenthe mid-1970s, these views have been
challenged by many experimental andchallenged by many experimental and
observational studies. For example, Jonesobservational studies. For example, Jones
& Benowitz (1976) administered oral& Benowitz (1976) administered oral
THC in doses of 70210 mg/day to subjectsTHC in doses of 70210 mg/day to subjects
for 30 days and noted a progressive loss offor 30 days and noted a progressive loss ofthe subjective `high'. This finding was repli-the subjective `high'. This finding was repli-
cated by Georgotas & Zeidenberg (1979),cated by Georgotas & Zeidenberg (1979),
who gave an average daily dose of 210 mgwho gave an average daily dose of 210 mg
THC to volunteers for a 4-week period THC to volunteers for a 4-week period
the subjects then ``found that the marijuanathe subjects then ``found that the marijuana
was much weaker''. Withdrawal signs werewas much weaker''. Withdrawal signs were
also found: during the first week of absti-also found: during the first week of absti-
nence the subjects ``became very irritable,nence the subjects ``became very irritable,
uncooperative, resistant and at timesuncooperative, resistant and at times
hostile''; they also became hungry andhostile''; they also became hungry and
experienced insomnia. These effects wanedexperienced insomnia. These effects waned
over 3 weeks. Cessation of smoked cannabisover 3 weeks. Cessation of smoked cannabis
has also been shown to lead to withdrawalhas also been shown to lead to withdrawalsymptoms (Haneysymptoms (Haney et al et al , 1999). The, 1999). The
cannabis-withdrawal syndrome has nowcannabis-withdrawal syndrome has now
been unequivocally demonstrated and in-been unequivocally demonstrated and in-
cludes restlessness, anxiety, dysphoria,cludes restlessness, anxiety, dysphoria,
irritability, insomnia, anorexia, muscleirritability, insomnia, anorexia, muscle
tremor, increased reflexes and autonomictremor, increased reflexes and autonomic
effects including changes in heart rate,effects including changes in heart rate,
blood pressure, sweating and diarrhoea.blood pressure, sweating and diarrhoea.The syndrome may appear in about 10The syndrome may appear in about 10
hours, and peaks at about 48 hourshours, and peaks at about 48 hours
(Mendelson(Mendelson et alet al, 1984)., 1984).
The validity of cannabisThe validity of cannabis
dependencedependence
TheThe Diagnostic and Statistical Manual ofDiagnostic and Statistical Manual of
Mental DisordersMental Disorders (DSMIV; American(DSMIV; American
Psychiatric Association, 1994) presentsPsychiatric Association, 1994) presents
criteria for the diagnosis of psychoactivecriteria for the diagnosis of psychoactive
substance dependence, based largely onsubstance dependence, based largely on
the concept of the dependence syndromethe concept of the dependence syndrome
(Edwards(Edwards et alet al, 1981). The key features of, 1981). The key features of
DSMIV substance dependence are cogni-DSMIV substance dependence are cogni-
tive, behavioural and physiological symp-tive, behavioural and physiological symp-
toms, indicating that the individualtoms, indicating that the individual
continues to use the substance despite signi-continues to use the substance despite signi-
ficant substance-related problems. Theficant substance-related problems. The
criteria include tolerance, a withdrawalcriteria include tolerance, a withdrawal
syndrome, difficulty in controlling con-syndrome, difficulty in controlling con-
sumption and a pattern of use which leadssumption and a pattern of use which leads
to a reduction in other important activities.to a reduction in other important activities.
In an empirical study, MorgensternIn an empirical study, Morgenstern et alet al
(1994) found the DSM concept of cannabis(1994) found the DSM concept of cannabis
dependence as least as valid as those fordependence as least as valid as those for
dependence on alcohol, opiates, stimulantsdependence on alcohol, opiates, stimulants
and sedatives.and sedatives.
Prevalence and course of cannabisPrevalence and course of cannabis
dependencedependence
From ECA data, Anthony & Helzer (1991)From ECA data, Anthony & Helzer (1991)
showed that men had a higher prevalenceshowed that men had a higher prevalence
(7.7%) of cannabis abuse or dependence(7.7%) of cannabis abuse or dependence
than women (4.8%). This was largely duethan women (4.8%). This was largely due
to the greater exposure to illicit drugs ofto the greater exposure to illicit drugs of
men, since the prevalence of a diagnosis ofmen, since the prevalence of a diagnosis of
abuse/dependence among those who hadabuse/dependence among those who had
used cannabis more than five times wasused cannabis more than five times wasthe same in men and women (21% andthe same in men and women (21% and
19%, respectively). Extrapolating from19%, respectively). Extrapolating from
these data, Hallthese data, Hall et alet al (1994) suggest that(1994) suggest that
about 17% of those who used cannabisabout 17% of those who used cannabis
more than five times would meet DSMIIImore than five times would meet DSMIII
criteria for dependence, and that for thosecriteria for dependence, and that for those
who have ever used there is approximatelywho have ever used there is approximately
a 1/10 risk.a 1/10 risk.
From a New Zealand birth cohort ofFrom a New Zealand birth cohort of
1265 children, Fergusson & Horwood1265 children, Fergusson & Horwood
(2000) found that by the age of 21, nearly(2000) found that by the age of 21, nearly
70% had used cannabis and over 9% met70% had used cannabis and over 9% met
DSMIV criteria for cannabis dependence.DSMIV criteria for cannabis dependence.Key predictors were male gender, ethnicKey predictors were male gender, ethnic
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JOHNSJOHNS
minorityminority status and measures of adoles-status and measures of adoles-
cent risk-cent risk-taking behaviours, includingtaking behaviours, including
cigarette smoking, conduct problems andcigarette smoking, conduct problems and
a delinquent peer group.a delinquent peer group.
WiesbeckWiesbeck et alet al (1996) set out to deter-(1996) set out to deter-
minemine the prevalence of the cannabis-the prevalence of the cannabis-
withdrawal syndrome in people who hadwithdrawal syndrome in people who hadused the drug but who were not in treat-used the drug but who were not in treat-
ment. In a cohort of 5611 individuals,ment. In a cohort of 5611 individuals,
31% had taken the drug on more than 2131% had taken the drug on more than 21
occasions in a year. Among these moreoccasions in a year. Among these more
frequent users, 16% met criteria for afrequent users, 16% met criteria for a
cannabis-withdrawal syndrome i.e. atcannabis-withdrawal syndrome i.e. at
least any one of the following: feelingleast any one of the following: feeling
nervous or irritable, insomnia, tremor,nervous or irritable, insomnia, tremor,
sweats, nausea, gastrointestinal disturbancesweats, nausea, gastrointestinal disturbance
or appetite change. These individuals hador appetite change. These individuals had
used the drug almost daily for an averageused the drug almost daily for an average
of 70 months and even when use of alcoholof 70 months and even when use of alcohol
and other drugs was considered, cannabisand other drugs was considered, cannabisuse was still significantly related to a self-use was still significantly related to a self-
report of a history of cannabis withdrawal.report of a history of cannabis withdrawal.
Thomas (1996) found that 35% ofThomas (1996) found that 35% of
cannabis users said that they could not stopcannabis users said that they could not stop
when they wanted to, 24% continued towhen they wanted to, 24% continued to
use despite problems attributed to the druguse despite problems attributed to the drug
and 13% felt that they could not controland 13% felt that they could not control
their consumption. Restlessness or irrit-their consumption. Restlessness or irrit-
ability if they could not use cannabis wasability if they could not use cannabis was
reported by 20% of those surveyed.reported by 20% of those surveyed.
Interestingly, dependent users were no moreInterestingly, dependent users were no more
likely to report panic or psychotic episodeslikely to report panic or psychotic episodes
than those classed as non-dependent. Withthan those classed as non-dependent. Withregard to untoward social consequences,regard to untoward social consequences,
14% of cannabis users agreed that the con-14% of cannabis users agreed that the con-
sumption of the drug had caused them tosumption of the drug had caused them to
neglect activities previously consideredneglect activities previously considered
important or enjoyable. These findingsimportant or enjoyable. These findings
(Thomas, 1996) have to be qualified by the(Thomas, 1996) have to be qualified by the
low overall response rate of 35%, the uselow overall response rate of 35%, the use
of unvalidated criteria for cannabisof unvalidated criteria for cannabis
dependence and by the lack of data ondependence and by the lack of data on
misuse of alcohol or other drugs among themisuse of alcohol or other drugs among the
sample.sample.
SwiftSwift et alet al (1998) interviewed a sample(1998) interviewed a sample
from New South Wales of 243 long-termfrom New South Wales of 243 long-termcannabis users who were smoking 34cannabis users who were smoking 34
times a week. A lifetime prevalence oftimes a week. A lifetime prevalence of
57% was found for both DSMIIIR and57% was found for both DSMIIIR and
ICD10 (World Health Organization,ICD10 (World Health Organization,
1992) dependence, but only a quarter per-1992) dependence, but only a quarter per-
ceived that they had a cannabis problem.ceived that they had a cannabis problem.
VULNERABILITYVULNERABILITY
TO ADVERSE EFFECTSTO ADVERSE EFFECTS
OF CANNABISOF CANNABIS
It has previously been emphasised thatIt has previously been emphasised thatconstitutional factors such as relativeconstitutional factors such as relative
youthfulness, personality and misuse ofyouthfulness, personality and misuse of
other drugs, may act as vulnerability factorsother drugs, may act as vulnerability factors
to the adverse mental effects of cannabis.to the adverse mental effects of cannabis.
Mental illness as a vulnerability factor hasMental illness as a vulnerability factor has
been reviewed in the previous section.been reviewed in the previous section.
AdolescenceAdolescence
There are a number of reasons why adoles-There are a number of reasons why adoles-
cence may be regarded as a time of vulner-cence may be regarded as a time of vulner-
ability for the adverse mental effects ofability for the adverse mental effects of
cannabis. First, adolescents may experiencecannabis. First, adolescents may experience
emotional problems that cue cannabis use,emotional problems that cue cannabis use,
and their relative youth may lead to anand their relative youth may lead to an
increased risk of adverse mental states onincreased risk of adverse mental states on
using the drug. Second, regular use ofusing the drug. Second, regular use of
cannabis may interfere with learning andcannabis may interfere with learning and
personal development. Last, early initiationpersonal development. Last, early initiation
of cannabis use may predict an increasedof cannabis use may predict an increased
risk of escalation in risk and progressionrisk of escalation in risk and progression
to other drugs.to other drugs.
With regard to the possible impact ofWith regard to the possible impact of
emotional problems, Newcombe & Bentleremotional problems, Newcombe & Bentler
(1988) found a strong relationship between(1988) found a strong relationship between
adolescent drug use and the experience ofadolescent drug use and the experience of
emotional distress, depression and lack ofemotional distress, depression and lack of
a sense of purpose in life. As to the prospecta sense of purpose in life. As to the prospect
of adverse mental states on using high dosesof adverse mental states on using high doses
of cannabis, this review has demonstratedof cannabis, this review has demonstrated
dose-related effects in adults and thedose-related effects in adults and the
younger user is not likely to be at any lesseryounger user is not likely to be at any lesser
risk. Crowleyrisk. Crowley et alet al (1998) found that for(1998) found that for
adolescents with conduct problems, canna-adolescents with conduct problems, canna-
bis use was not benign in that misuse wasbis use was not benign in that misuse was
associated with high rates of dependenceassociated with high rates of dependence
and withdrawal.and withdrawal.
The possible effects of cannabis con-The possible effects of cannabis con-
sumption on the educational performancesumption on the educational performance
of adolescents are not easy to demonstrateof adolescents are not easy to demonstrate
in population studies (Hallin population studies (Hall et alet al, 1994)., 1994).
Newcombe & Bentler (1988), having con-Newcombe & Bentler (1988), having con-
trolled for the higher nonconformity andtrolled for the higher nonconformity and
the lower academic potential amongthe lower academic potential among
adolescent drug users, found only a modestadolescent drug users, found only a modest
negative link between drug use and collegenegative link between drug use and college
involvement. Schwartzinvolvement. Schwartz et alet al (1989) found(1989) foundshort-term memory impairment in 10short-term memory impairment in 10
cannabis-dependent adolescents comparedcannabis-dependent adolescents compared
with matched controls. Test results tendedwith matched controls. Test results tended
to improve over 6 weeks, which suggestedto improve over 6 weeks, which suggested
that the deficits observed were due to pastthat the deficits observed were due to past
cannabis use.cannabis use.
Polydrug usePolydrug use
A substantial number of young people inA substantial number of young people in
the community use a range of drugs whichthe community use a range of drugs which
includes cannabis. Ramsay & Percyincludes cannabis. Ramsay & Percy
(1996) found that 4% of a group of 16-(1996) found that 4% of a group of 16-
to 29-year-olds admitted using cannabisto 29-year-olds admitted using cannabisand other drugs in the past month, byand other drugs in the past month, by
contrast with 8% who had used only can-contrast with 8% who had used only can-
nabis. Clinical observation suggests thatnabis. Clinical observation suggests that
cannabis users who also misuse other drugscannabis users who also misuse other drugs
or alcohol seem to experience more severeor alcohol seem to experience more severe
mental health problems than those whomental health problems than those who
solely take cannabis, but there do notsolely take cannabis, but there do not
appear to be any substantial publishedappear to be any substantial publishedstudies on this issue. Polydrug use is astudies on this issue. Polydrug use is a
recognised concern in psychiatric popula-recognised concern in psychiatric popula-
tions: for example, Baigenttions: for example, Baigent et alet al (1995)(1995)
found that 20% of their dual-diagnosisfound that 20% of their dual-diagnosis
#patients misused more than one substance.#patients misused more than one substance.
PersonalityPersonality
Given the heterogeneity of the populationGiven the heterogeneity of the population
of cannabis users, it is not surprising thatof cannabis users, it is not surprising that
no single personality type or disorder isno single personality type or disorder is
particular to users of that drug or, indeed,particular to users of that drug or, indeed,
to users of any illicit drug (Allen & Frances,to users of any illicit drug (Allen & Frances,
1986). However, it is a matter of clinical1986). However, it is a matter of clinical
observation that the use of cannabis byobservation that the use of cannabis by
some individuals seems to be predisposedsome individuals seems to be predisposed
by traits such as social anxiety, anxiety orby traits such as social anxiety, anxiety or
dysphoria. Such posited use as a form ofdysphoria. Such posited use as a form of
self-medication to relieve unwanted affectsself-medication to relieve unwanted affects
or feelings was not corroborated in a studyor feelings was not corroborated in a study
of cannabis-dependent individuals (Greeneof cannabis-dependent individuals (Greene
et alet al, 1993). There is good evidence for, 1993). There is good evidence for
the comorbidity of drug misuse and somethe comorbidity of drug misuse and some
personality disorders. For example, Regierpersonality disorders. For example, Regier
et alet al (1990) report that some form of(1990) report that some form of
substance abuse was identified in 83.6%substance abuse was identified in 83.6%
of individuals with antisocial personalityof individuals with antisocial personality
disorder (ASPD), with an odds ratio ofdisorder (ASPD), with an odds ratio of
29.6. It should be appreciated that this very29.6. It should be appreciated that this very
high rate arises because substance abuse ishigh rate arises because substance abuse is
one of the major diagnostic criteria forone of the major diagnostic criteria for
ASPD; only 16% of individuals with ASPDASPD; only 16% of individuals with ASPD
did not have a history of substance abuse.did not have a history of substance abuse.
The same study showed that the lifetimeThe same study showed that the lifetime
prevalence of ASPD in cannabis abuse orprevalence of ASPD in cannabis abuse or
dependence was 14.7% with an odds ratiodependence was 14.7% with an odds ratio
of 8.3. The interaction between ASPD andof 8.3. The interaction between ASPD and
cannabis use is too complex to explore atcannabis use is too complex to explore at
length in this review, but it is probable thatlength in this review, but it is probable thateach disorder exacerbates the adverseeach disorder exacerbates the adverse
effects of the other. See Dolan & Coideffects of the other. See Dolan & Coid
(1993) for a discussion of factors determin-(1993) for a discussion of factors determin-
ing outcome in ASPD.ing outcome in ASPD.
Implications for mental health careImplications for mental health care
How should mental health services respondHow should mental health services respond
to these findings? The key priorities are: (a)to these findings? The key priorities are: (a)
risk-management and care-planning haverisk-management and care-planning have
to be informed by a thorough substance-to be informed by a thorough substance-
misuse assessment (Johns, 1997); (b) com-misuse assessment (Johns, 1997); (b) com-
munity and in-patient psychiatric servicesmunity and in-patient psychiatric services
should develop policies on substance useshould develop policies on substance usewhich balance the treatment needs ofwhich balance the treatment needs of
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individual patients with duties of care toindividual patients with duties of care to
other patients and to the general public;other patients and to the general public;
and (c) research is needed into treatment in-and (c) research is needed into treatment in-
terventions for patients with mental illnessterventions for patients with mental illness
and substance misuse problems.and substance misuse problems.
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Anthony, J. C. & Helzer, J. E.Anthony, J. C. & Helzer, J. E. (1991)(1991) Syndromes ofSyndromes of
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12 11 21
CLINICAL IMPLICATIONSCLINICAL IMPLICATIONS
&& Among those who have ever taken cannabis,1/10 are at riskof dependence.Among those who have ever taken cannabis,1/10 are at risk of dependence.
&& Heavy cannabis misuse leads to the risk of psychotic episodes, and aggravates theHeavy cannabis misuse leads to the risk of psychotic episodes, and aggravates the
symptoms and course of schizophrenia.symptoms and course of schizophrenia.
&& For any psychiatric patient, risk-management and care-planning is incompleteFor any psychiatric patient, risk-management and care-planning is incomplete
without a thorough assessment of substance misuse.without a thorough a ssessment of substance misuse.
LIMITATIONSLIMITATIONS
&& The available literature shows a preponderance of case reports and uncontrolledThe available literature shows a preponderance of case reports and uncontrolled
studies.studies.
&& Epidemiological findings from one setting cannot be assumed to generalise toEpidemiological findings from one setting cannot be assumed to generalise to
other cultural groups.other cultural groups.
&& It is not easy to determine causal explanations from the studies cited.It is not easy to determine causal explanations from the studies cited.
ANDREW JOHNS, FRCPsych, Depar tment of Forensic Psychiatry, Institute of Psychiatry, De Crespigny Park,ANDREW JOHNS, FRCPsych, Department of Forensic Psychiatry, Institute of Psychiatry, De Crespigny Park,
Denmark Hill,London SE5 8 AF. Tel: 020 7919 3123Denmark Hill, London SE5 8 AF. Tel: 02 0 7 919 3123
(First received 22 July 1999, final revision 4 September 200 0, accepted 6 September 20 00)(First received 22 July 1999, final revision 4 September 200 0, accepted 6 September 20 00)
-
7/29/2019 Psychiatric Effects of Cannabis 8p
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