Herbal medicines put into context

Their use entails risks, but probably fewer than with synthetic drugs

Recent reviews have rightly alerted us to the risk associated with herbal medicines.1 This is necessary and important. But the more important question probably is–do the risks of herbal benefits outweigh their potential for harm? Therefore I will try to put herbal medicines into context and consider the benefit they might bring.

The potential benefits of herbal medicines could lie in their high acceptance by patients, efficacy, relative safety, and relatively low costs. Patients worldwide seem to have adopted herbal medicines in a major way. Survey data from the United Kingdom show that herbal medicine has been tried by about 30% of the British population.2 The associated out of pocket expenditure was estimated to amount to £31m (US$47.7m; €45m) in the United Kingdom2 and £1.3bn in Germany.3 Herbal medicines are used predominantly for minor and self limiting indications, with respiratory tract infections heading the list.3 But even for those conditions the remarkable acceptance of herbal medicines can be a good thing only if they can be shown to do more good than harm at reasonable cost.

The efficacy of herbal medicines has been tested in hundreds of clinical trials, and it is wrong to say that they are all of inferior methodological quality. But this volume of data is still small considering the multitude of herbal medicines–worldwide several thousand different plants are being used for medicinal purposes.4 A recent overview included 23 systematic reviews of rigorous trials of herbal medicines.5 Eleven came to a positive conclusion, nine yielded promising but not convincing results, and three were negative. The relative paucity of rigorous clinical trials is mostly due to the fact that, compared with the pharmaceutical sector, the herbal industry is small and can rarely afford the considerable expense of a clinical trial. Sadly the traditional use directive, which sets out to harmonise the registration of herbal medicines in the European Union,6 lacks any incentive for companies to invest further into research. Public funds are only very rarely dedicated to research in this area.7

Even though herbal medicines are not devoid of risk,1 they could still be safer than synthetic drugs. Between 1968 and 1997, the World Health Organization's monitoring centre collected 8985 reports of adverse events associated with herbal medicines from 55 countries.8 Although this number may seem impressively high, it amounts to only a tiny fraction of adverse events associated with conventional drugs held in the same database.8 However, the relative paucity could also be due to a relatively higher level of underreporting. More conclusive evidence on the relative risks of herbal medicine versus synthetic drugs is scarce. Linde et al showed that the herbal antidepressant St John's wort has only about half the rate of adverse effects compared with conventional antidepressants.9 Kava, an effective herbal anxiolytic,10 has recently been banned in several countries, including the United Kingdom, because of the suspicion that, in rare cases, it causes hepatotoxicity. None the less, preliminary data indicate that it probably is still safer than benzodiazepines.11 At present the relative safety of herbal medicines is undefinable, but many of the existing data indicate that adverse events, particularly serious ones, occur less often than with prescription drugs.4

A further strength of herbal medicines is that they are inexpensive, at least this is what the “herbal lobby” wants us to believe. The truth, however, is that almost no conclusive cost evaluation studies are available.12 Many, but by no means all, herbal medicines are inexpensive to buy; the potential for cost savings by using more herbal medicines could therefore be substantial–at present, however, we simply cannot be sure.

Thus the evidence on herbal medicines is incomplete, complex, and confusing. They are certainly associated with both risks1 and benefits.4 As more and more people try herbal medicines, the pressure increases on healthcare professionals to be well informed about the subject, and on researchers to fill the many and somewhat embarrassing gaps in our current knowledge. Failing to do (and fund) this work would, in my view, constitute the true risk associated with herbal medicines.