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Negative effects of herbal medicines

The simple fact that herbal medicines are drugs is underappreciated or not understood at all

 by most people. They include good drugs, bad drugs and completely useless drugs, but they

are drugs nonetheless, and therein lies a lot of grief.

Herbal medicines are often promoted as “natural” (and therefore gentle). People tend to think

of a relaxing cup of chamomile tea made from ingredients hand-picked by benevolent

 beaming grannies in an Arcadian setting. But while the implication is that “natural” is good,

the majority of the most toxic compounds we know of are natural.

Natural toxins

Botulinum toxin is 100% natural and the most deadly substance known on this planet. Yet

suitably diluted Botulinum toxin is used to relieve intractable muscle spasms (as well as make

the skin less wrinkly by paralysing muscles with Botox).

While the vast majority of herbal medicines are not as dramatically lethal as Botulinum toxin,

virtually all will have some adverse effects. Indeed, any substance that alters your body’s

 physiology will have side effects.

After all, the main reason that there so many chemicals in plants that we can use as medicines

is that they are used as defences. So they interfere with some aspect of physiology to stop

animals eating them (morphine, caffeine, Tetra-Hydro Cannibidiol in marijuana and those

lovely aromatic oils in Eucalyptus oil are some well-known examples). Or they provide

defence against infection (salicylic acid in willow bark, for instance).

So you would expect some side effects.

Extract of foxglove is effective for treating heart failure, but get the concentration wrong and

it is lethal; willow bark is effective for reducing pains and fever but causes ulceration of the

mouth and throat if used for a while; and Senna pods are used to relieve constipation, but can

cause heart problems and gastrointestinal damage. 

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Drug interactions

What’s more concerning is that since people don’t think of herbal medicines as drugs, they

also don’t consider they will interact with their other medicines. But they do. 

St John’s Wort enhances the effects of any prescribed antidepressants, leading to potentially

lethal overdose. John Tann/Flickr , CC BY 

The poster child for drug-herb interactions is St. John’s Wort –  because it has a twofold

effect. The compounds in it that are responsible for its antidepressant effect will enhance the

effects of any prescribed antidepressants, leading to potentially lethal overdose.

 Not only does St. John’s Wort interact with antidepressants, the chemicals in it also stimulate

the liver to  break down certain classes of drugs more rapidly. People taking the herb have

 been endangered because their  anti-rejection drugs or  anti-HIV drugs have been broken down

 below effective therapeutic levels.

Despite the side effects of St. John’s Wort being well known in the pharmaceutical

community, information about them from points of sale are generally very poor  and most

consumers will be unaware of them (see also here).

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And it’s not just St. John’s Wort. A whole range of herbal medicines interact with

conventional medicines (dandelion and diuretics is another example). This puts people in

harms way when they are prescribed conventional drugs.

Because most people don’t think herbal medicines are drugs, they tend not to tell their

medical practitioner  about their herbal use. And medical practitioners tend not to ask about

specifically about it as they expect their patients will tell them!

Missing ingredient

But if herbal medicines have such a range of adverse effects, why don’t we see more

evidence of them? There are three reasons for this.

First, although figures for complementary medicine show roughly half of Australians taking

complementary medicines, these are mostly vitamins (which have their own problems). Far

fewer people actually take herbal medicines.

In a study of antidepressant use in New South Wales, for instance, very few people were

taking St. John’s Wort, and even fewer were taking it together with conventional

antidepressants.

Second, adverse reactions to herbal medicines are significantly under reported. While there is

a “blue card” system for reporting adverse events to conventional medicines, herbal

medicines are often bought from health-food stores, or prescribed by herbalists who don’t

 participate in the system.

So there’s no way for most herbal medicine buyers to report adverse events.  

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Extract of foxglove is effective for treating heart failure, but get the concentration wrong and

it is lethal. e_chaya/Flickr , CC BY 

Finally, there’s some evidence that many herbal medicines have very low amounts of the

active ingredients, or  do not have the active ingredient at all. So many herbal medicines are

no more than expensive placebos.

Learn to distrust

Most herbal medicines are classified as “Listed” by the Therapeutic Goods Administration. 

This means that unlike registered medicines such as paracetamol and statins, the evidence

required for approval is much less stringent.

In fact, it’s basically an honour system where the herbal medicines sponsor says there’s no

evidence of harm, and we hold documentation that shows this. Mostly, the evidence is

historical, claiming that people have been using it for generations without evidence of harm.

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But a long history of use is not necessarily evidence of no harm. Willow bark, for instance,

has as long a history of causing ulcers as it has of relieving pain, but its serious side effects

have not passed into lore.

Until we used modern medical investigation, we were unaware of  the harms caused by the

herb borage, and the severe kidney toxicity and cancer caused by the Aristolochic acid found

in herbs used in traditional medicine. 

Herbal medicines are widely trusted but that trust is mostly due to our imagination coupling

them with a bucolic vision of nature which never existed. It’s time to end this misplaced trust

and start seeking evidence.

We still only have a very poor idea of the potential harms posed by the panoply of herbal

medicines on sale.

This is the second art icle in our series about complementar y and alternative therapies.

Cli ck on the links below to r ead the others:  

 

Here’s why we should research alternative therapies 

Can we scienti f icall y test herbal medicines?  

  Yes: Quality research of herbal medicines is possible 

 

 No: We can’t have reliable evidence for herbal therapies