This site is intended for health professionals only
MD PhD FRCP FRCPEd
Peninsula Medical School
Universities of Exeter & Plymouth
Herbal medicine, the medical use of preparations that contain exclusively plant material, can be seen as the predecessor of pharmacology; even today, a large proportion of our modern drugs are plant-based.(1) It became less important when synthetic drugs began to conquer the world of therapeutics, but people have again started voting with their feet and wallets in favour of herbal medicine. Their popularity in the USA, for instance, increased by a respectable 380% between 1990 and 1997.(2)
Usage by cancer patients
Cancer patients are no exception. Table 1 summarises data from several recent surveys.(3–10) While they differ in many respects, they agree that many people try herbal medicines when faced with a diagnosis of cancer. We recently evaluated the most popular websites for “alternative” cancer treatments and found that a confusing plethora of herbal medicines was recommended to cancer patients, with little consensus as to which herbal remedy should be used.(11) This finding is strikingly similar to our analysis of seven leading general texts of “alternative” medicine aimed at lay people. In total the seven authors recommended a bewildering array of 133 different “alternative” treatments for cancer, with an almost total absence of agreement among them (Table 2).(12)
This obviously begs the question as to why alternative therapies are currently so very popular. There is no simple answer to this question. The reasons range from frustration with conventional medicine, desperation, philosophical congruence, the desire to gain control over one’s own health, to aspects of the good therapeutic relationship with providers of alternative medicine.(12) Cancer patients in particular are prone to try any treatment for which someone, somewhere, makes positive claims. Few seem to ask what the substance of these claims may be.
One crucial question is, clearly, do herbal medicines work? It is, I think, important to point out that herbal medicines can be used in at least three different ways:
We recently systematically reviewed the evidence for all three approaches.(12)
In cancer prevention there are several herbal medicines that are supported by encouraging evidence: garlic, green tea and ginseng. All three are as much dietary habits as they are herbal medicines. The evidence for all of them is tantalising; it is based mostly on epidemiological data demonstrating that the regular consumption of these herbal medicines or foods conveys a degree of protection against developing (mostly gastrointestinal) cancer in later life. Such evidence is unfortunately not fully convincing; numerous confounders (eg, a generally healthier lifestyle of one group) could have produced false-positive findings. However, the data are sufficiently encouraging to be submitted to further study.
Most of the herbal medicines listed in Table 2 are promoted as cancer “cures” – that is, treatments that reduce the tumour burden or otherwise prolong the life of cancer sufferers. In our systematic review, we found trial data for the following herbal medicines/mixtures: aloe vera, destagnation, essiac, mistletoe, PC-SPES, sho-saiko-to and St John’s wort.(12) For none of them was the evidence anywhere near the point where we could rate it as convincing. In most cases there were only single trials, which also were often methodologically weak. We concluded that there is not a single herbal remedy that is of proven benefit as a cancer therapy. If, one day, an effective herbal medicine does emerge, it would certainly be instantly adopted by conventional oncology.
The aim of cancer palliation/support is not to eliminate the cancer but to enhance the quality of life of patients. While several alternative therapies (eg, acupuncture) show much promise in this respect, we found no trial data relating to herbal medicines.(12) Yet there is much indirect evidence (ie, trial data derived from patient groups not afflicted by cancer) that some cancer-associated symptoms might favourably respond to herbal treatments:(12)
As with all pharmacological agents, herbal medicines can cause adverse effects. Even though the media often try to tell us differently, none of the above-named herbal treatments is totally devoid of adverse effects (Table 3). By and large these adverse effects are mild and might seem minor compared with those of oncology drugs. Unfortunately, this does not mean that the risks of herbal medicine are generally negligible. Because they are marketed as dietary supplements in most countries, herbal medicines are not as strictly controlled for quality as licensed medicines. As a result, it has repeatedly been shown that herbal mixtures (particularly Asian preparations) are often contaminated (eg, with heavy metals) or adulterated (eg, with prescription drugs).(13)
As with all pharmacological agents, herbal medicines might interact with prescribed drugs.(14) This is a vast subject that, so far, has been much neglected by systematic research. Our knowledge is therefore highly fragmentary. Considering that practically all cancer patients take multiple prescribed drugs, the potential for herb–drug interactions in this patient group is considerable. Some potentially important interactions are listed in Table 3. Foremost this table reveals just how incomplete our knowledge really is.
Talking to patients
Cancer patients often do not tell their doctor about their use of herbal medicines. Pharmacists may be the only conventional healthcare professional in contact with patients regarding herbal medicine. When advising cancer patients, I recommend considering the following:
American Cancer Society. Guide to complementary and alternative cancer methods. Atlanta, GA, USA: American Cancer Society; 2000.
(A thorough and objective book for patients to obtain essential information in this area)
Ernst E, Pittler MH, Stevinson C, White AR. The desktop guide to complementary and alternative medicine. Edinburgh: Mosby; 2001.
(A strictly evidence-based approach to all aspects of complementary medicine)
Cassileth BR, Lucarelli CD. Herb–drug
interactions in oncology. Hamilton, Ontario:
BC Decker; 2003.
(An authoritative reference book with full information on herbal and other supplements)