Traditional Herbal Medicines: a Guide to Their Safer Use Drs Lakshman Karalleidie & Indika Gawarammana ( with editorial advice from Debbie Shaw ). Published by Hammersmith Press , London , 2008 . ISBN 978-1-905140-04-6 . 376 pp, soft back, £18.99.

As a pharmacology student I was taught that ‘alkaloids’ are basic drugs derived from plants. Atropine, nicotine, tubocurarine, quinine, ephedrine, cocaine, morphine and the rest featured heavily in the course both as therapeutic drugs and as tools for investigating physiological function. Pure substances are extracted from natural sources (vegetable, fungal, microbial or animal) using a variety of physical chemical separative techniques coupled with bioassay to identify fractions where activity is located. This leads to the identification of pure substance (or substances) and is followed by structural analysis and chemical synthesis of the pure drug. Many such drugs remain in first-line therapeutic use, and many others formed the starting point for the synthesis of chemical variants with more selective biological activities, or other desirable properties. Many of today's drugs were derived in this way, and so it comes as no surprise to the practitioner of scientific medicine that herbs contain substances with potent biological activities that may cause either good or ill. Pharmaceutical scientists looking for leads remain interested in natural products and traditional herbal remedies for this reason.

Distinct from this rational interest in a potential source of new drugs, many patients take herbal remedies for numerous unproven indications in hopes of therapeutic benefit. Since these herbal preparations are of variable quality and potency, and since their safety and efficacy are seldom well documented, one might assume that such use would be in decline, but the reverse is true, with massive (multi-billion dollar) worldwide commercial activity. Why should this be? Many such patients suffer from symptoms of chronic diseases (psychological or organic) that are not well catered for by conventional medical treatment. Herbal remedies are widely used by patients with serious organic disease (including HIV infection and malignant diseases) as well as symptoms such as sexual disorder, headache, chronic fatigue and so on, which, while seldom evidence of life-threatening disease, can make life miserable. Such individuals often prefer to avoid conventional drugs, fearing (reasonably) that these may cause adverse effects. Some believe (less reasonably) that the ‘naturalness’ of herbal medications implies that these are safe. Many such people do not mention to their doctor that they are taking an alternative treatment instead of, or as well as, conventional drugs.

A surprisingly large number of general practitioners recommend treatment with herbal medication, some, no doubt, in the hope that this will provide comfort or hope to patients who dislike taking conventional medication. Unfortunately, the evidence base demonstrating safety and efficacy is deficient, and such treatment may cause more harm than good. It might be hoped that quality assurance of medical education would ensure that qualified doctors have been trained in evidence-based medicine and can advise their patients accordingly, but in the UK quality assurance of university education by the Quality Assurance Agency (QAA) is designed to monitor processes (teaching and assessment methods) rather than the content of degree courses. Consequently, as pointed out by David Colquhoun in a letter to the Times, it would be possible to provide a degree in witchcraft which would be entirely acceptable to the QAA.

Is Traditional Herbal Medicines a textbook of witchcraft? I was a little anxious as to this possibility when I read its subheading (‘a Guide to their Safer Use’), and indeed its authors do explore sympathetically treatment options provided by herbal medicine, with lists of herbs used in the treatment of a wide range of common medical disorders, including severe diseases for which there are conventional (‘allopathic’) alternatives with good evidence of efficacy. It is particularly this opening chapter with which the present reviewer has serious reservations, but I found the subsequent chapters considerably more rewarding. Notwithstanding their clearly stated commitment to traditional herbal medicines, the authors are distinguished clinicians with considerable experience in human toxicology.

Alternative medicine (including herbal medicine) arouses strong emotions, and much Western writing on the subject is adversarial, taking the form either of ‘debunking’ or, contrariwise, of hot polemic from alternative medicine practitioners. Lakshman Karalleidie (a recently retired anaesthetist, expert in poisoning and drug interactions and currently working with the Health Protection Agency) and Indika Gawarammana (a Senior Lecturer in Medicine practising in Sri Lanka) approach the subject from a completely different angle, taking the pragmatic view that since herbal medication is so common, it is crucial for patient safety that several distinct constituencies (conventional practitioners, herbalists, users) share some common ground even while agreeing to differ over evidence of efficacy. Debbie Shaw, who works closely with the Royal Botanic Gardens Kew, provided editorial advice.

Conventional education of schoolchildren (patients to be) and conventional training of medical students and junior doctors have not led to a withering away of unproven and potentially harmful herbal medicines of uncertain efficacy. The authors' approach is that such practice has been going on for a very long time (e.g. ayurvedic and other traditional approaches) and, like it or not, is likely to continue to do so for the foreseeable future. The authors accept this as a fact of life, but try to minimize the harm that herbal medication can cause. This they do in a low-key, nonpolemical and systematic way by describing the herbs, what they are used for (without addressing the evidence base), what effects are known and what adverse effects are either known or to be anticipated.

One important part of the book is directed to herbal practitioners and will alert them to clinical features associated with symptoms for which patients commonly seek herbal remedies but which should act as warning flags for the need for conventional investigation. (For example, aspects of the history that raise a suspicion of raised intracranial pressure in a patient with headaches.) Another aim is to inform conventional practitioners of the indications for which their patients may be taking herbal medications and the kinds of problems that may ensue. Such problems may occur as a result of direct toxicity of pharmacologically active components. All drugs are poisons (as observed by Paracelsus), the difference lying in the dose. Atropine (from deadly nightshade) is named for Atrope, the fate who cuts the life-line. Botulinum toxin is another natural product where getting the dose wrong may have unfortunate consequences. Conventional medicine readily puts the pure forms of such drugs to good and safe use, but uncontrolled batch-to-batch variations in potency would be problematic in a crude extract. Recent problems with herbal medicines highlighted by the Medicines and Healthcare products Regulatory Agency (MHRA) include severe toxicity to liver, kidneys and blood. In addition to direct toxicity, problems may result indirectly as a result of drug–herb interaction. Such problems are not trivial: some herbs (e.g. St John's wort) contain potent P450 enzyme inducers, and interactions (e.g. with immunosuppressant therapy following transplantation) can be expected to lead to catastrophic outcomes (e.g. graft rejection) or to unwanted pregnancy (due to failure of the contraceptive pill). Herbal medication use contributes to the great variability between individuals in their responses to conventional drugs.

I was initially surprised by how much of the book is devoted to inorganic metals. From student days I recalled that alongside alkaloids, metals such as arsenic and mercury have been used for centuries for their supposed therapeutic properties (‘a night with Venus, a lifetime with Mercury. . . .’ as the saying went, until Ehrlich's discovery of salvarsan rendered calomel obsolete for the treatment of syphilis). I had not, however, appreciated the extent to which herbal and other traditional medicines are accidentally contaminated or deliberately supplemented with heavy metals. The resulting toxicities (especially neurotoxicity) can be insidious, difficult to diagnose and clinically devastating. Much toxicity from herbal remedies is probably chronic and cumulative, and it seems likely that adverse effects of such medication are under-appreciated, especially in vulnerable groups such as children and the elderly (both specifically addressed in this book). More reprehensible than the traditional (if injudicious) use of heavy metals is the deliberate adulteration of herbal medications with drugs (e.g. steroids, nonsteroidal anti-inflammatory drugs, oral hypoglycaemics). Such criminal activity is investigated and, where detected, prosecuted by drug regulatory authorities (such as the Food and Drug Administration and MHRA). Regulatory agencies are paying increasing attention to herbal medications, and practitioners, pharmacists and patients should be aware that in the UK confidential suspected adverse reaction reports (‘Yellow cards’) can be sent to the regulatory agency when they encounter toxicities or interactions that they suspect may be due to herbal medicines.

Finally, this book will be of considerable interest to intelligent potential users, who will become acquainted with the wide range and severity (e.g. death, liver failure with consequent need for liver transplantation) of adverse effects caused by some herbal products. My warning to them would be that when confronted with a list of (say) 38 herbs ‘used in the treatment of asthma’ (from aloe vera to yerba santa) they should bear in mind that this does not imply that these herbs actually work, or that they are safe, only that they are used. (One should not extrapolate that because they are used that they necessarily work or are safe.) Some of them certainly have pharmacological activities on airway smooth muscle (e.g. ephedra, number 15 on the list), but the evidence base for risk–benefit is not touched on, and no attempt is made to compare efficacy of herbal and allopathic medicines for medical disorders. The potential patient seeking enlightenment as to which herbal medicine to take for their symptom will be disappointed; for that, I fear, he would have to turn to the textbook of witchcraft. But he (or often she) will learn the difference between a herbal medicine and a placebo, and learn a great deal about the dangers of treatment with herbal medicines.

With the above provisos, the book is a nicely produced and fascinating account of the science (particularly the toxicology) surrounding the widespread and increasing consumption of herbal medications. Educators and evidence-based practitioners have so far signally failed to stem the tide of alternative medicine, and I would recommend them to take this very original book in liberal doses together with a (very) small pinch of gentian [the penitential purple, applied externally (p.152), noting that ‘some herbalists recommend avoidance during pregnancy and in patients with high blood pressure’].