There is a tendency among some people to assume that herbal medicines are safe, since they’re “natural”. However, those that work (many are found not to work when they’re actually studied properly) act because a chemical in the herbal medicine has an effect on the body, just like any pharmaceutical drug. Since many pharmaceutical drugs were derived from herbal medicines, you would think this would be evident, but that doesn’t seem to stop people from assuming they’re safe.
Unlike pharmaceutical drugs, natural products are often available without consulting a medical doctor. They also are not subject to the same level of regulation and control; most not only haven’t been properly tested to see if they work, but also haven’t undergone rigorous safety studies. Furthermore, the purity and potency of these products generally aren’t regulated ; as a result the dose of the active chemical is often unknown (and in some cases it isn’t always present), and contamination of herbal products or misidentification of plants have been reported . The natural products industry has aggressively resisted regulation in Canada and many other countries, however.
I’m not suggesting all herbal products are dangerous; many have been used for a long time without obvious adverse effects (though chronic effects can’t be ruled out without proper testing). However, one concern that probably doesn’t get as much attention as it should is the potential for drug interactions, some of which can be lethal. This risk is compounded by these products being available without consulting a doctor – often a doctor doesn’t know which herbal products a person is taking.
St. John’s wort, commonly used to treat depression among other disorders, is known to have a variety of potential drug interactions. Several studies [2,3,4,5] have reported interactions with warfarin; basically, a chemical called hyperforin in St. John’s wort is believed to increase metabolism of warfarin, resulting in a decrease in the concentrations of warfarin in the blood, preventing it from performing its potentially life-saving function. It can also interact with cyclosporine, used in organ transplants to prevent rejection, again significantly reducing the effects of this drug; it also increases the effectiveness of some antiretroviral drugs (such as those used to treat people with AIDS), some anti-cancer drugs (such as irinotecan), antiarrhythmic drugs such as digoxin, and more [3,6]. Several of these drugs are used for very serious conditions, and decreasing their effectiveness can have significant and possibly lethal implications
A variety of other herbal medicines are believed to affect warfarin, including garlic, gingko biloba, dong quai, danshen, devil’s claw, Chinese red sage, red yeast rice and red aven; some of these products increase the effects while others decrease it [3,4,5,7]. Garlic, gingko, Echinacea, ginseng and kava are all believed to interact with anticancer drugs, potentially affecting the success of treatments . Ginkgo has also been assocaited with a serious interaction with trazodone (a sedative and anti-depressant), resulting in a coma [3,4]. Liquorice can interact with antiarrythmic drugs such as digoxin . Tamarind can increase the bioavailability of aspirin, leading to gastrointestinal bleeding [1,2], while echinacea can increase the liver effects of acetaminophen (Tylenol)  – though this latter effect is only likely to be significant in the event of an overdose.
These are only a few of the known interactions between herbal medicines and pharmaceutical drugs, and this is only one of the hazards of herbal medicines. Interactions of herbal medicines with each other are certainly possible, as are unwanted side effects and toxic effects from high doses, just like any other drug. I’m not even considering the potential for effects resulting from contamination or plant mis-identification.
What this means is that, if you are taking herbal medicines of any kind, it is important to inform your doctor, particularly if you are taking any pharmaceutical drugs or have a serious illness. It is also critical that governments start to regulate the natural products industry better, including requirements for efficacy and safety testing.
1. Abebe, W. 2002. Herbal medication: potential for adverse interactions with analgesic drugs. Journal of Clinical Pharmacy and Therapeutics 27: 391-401.
2. Fugh-Berman, A. 2000. Herb-drug interactions. Lancet 2000 355: 134-138.
3. Coxeter, P.D., A.J. McLachlan, C.C. Duke and B.D. Roufogalis. 2004. Herb-drug interactions: an evidence based approach. Current Medicinal Chemistry 11: 1513-1525.
4. Izzo, A.A. 2004. Herb-drug interactions: an overview of the clinical evidence. Fundamental & Clinical Pharmacology 19: 1-16.
5. Myers, S.P. 2002. Interactions between complementary medicines and warfarin. Australian Prescriber 25(3): 54-56.
6. Williamson, E.M. 2003. Drug interactions between herbal and prescription medicines: review article. Drug Safety 26(15): 1075-1092.
7. Bergner, P. 1997. Herb-drug interactions. Medical Herbalism 9(2).
8. Sparreboom, A., M.C. Cox, M.R. Acharya and W.D. Figg. 2004. Herbal remedies in the United States: Potential adverse interactions with anticancer agents. Journal of Clinical Oncology 22(12): 2489-2503.