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Toxicity and adverse effects of herbal complementary therapy

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Jennifer Kelly, MSc, BA (Hons), RN, DipN, DipNEd.

Senior Lecturer, Homerton School of Health Studies, Cambridge

In recent years the use of complementary and alternative therapies has grown, so that there are now around 180 different therapies practised in the UK, with one-third to one-half of the general population using one or more forms of these therapies (BMA, 1993; Ernst, 1996a).

This growth has been fuelled by an increasing public concern with mainstream medicine coupled with a belief that, because many of these alternative/complementary therapies are ‘natural’ and have been around for a long time, they are safe. Other advantages that complementary/alternative therapies appear to offer over orthodox medicine are increased patient involvement and choice, a holistic rather than a reductionist approach, and a more humanistic therapist who gives patients time to express their needs while providing continuity of care. Modern medicine has failed some patients, and alternative therapies offer them hope, by helping them to make sense of their illness and treat ill-defined symptoms. The beliefs underpinning many alternative therapies can explain illness when science cannot (Zollman and Vickers, 2000).

Classifying therapies

Complementary and alternative therapies differ in that the former are treatments that can work alongside and in conjunction with orthodox medical treatments, while the latter are those given in place of orthodox medicine and whose effects may be negated by orthodox medicines (BMA, 1993).

Classifying any treatment as one rather than the other, however, is open to debate (Micozzi, 2001). Thus, for example, the BMA (1993) classifies massage, acupuncture and aromatherapy as complementary therapies, and herbals as alternative therapies, while Dunning et al (2001) classify them all as complementary.

Studies have shown that patients both consult their GP and use non-conventional therapies for the same illness episode (Fulder and Munro, 1985; Murray and Shepherd, 1988). Therefore in the following discussion the term ‘complementary’ will be used throughout.


There are a number of concerns in relation to complementary therapies. These include the problem that patients may see unqualified practitioners because, to date, only osteopathy has gained legislative power to sanction individuals guilty of malpractice (Rankin-Box, 2001). While patients are utilising therapies other than orthodox ones, there is also a fear that they risk missed or delayed diagnosis, may waste money on ineffective treatments and may refuse or cease effective orthodox treatments. Furthermore, it is argued, the mechanisms of some therapies are so implausible that they cannot possibly be effective.

These objections, however, are made from within an orthodox medical paradigm and are therefore open to question. Perhaps of greater concern is the belief that complementary therapies are universally safe. This is fallacious - all treatments have the potential to do harm as well as good; indeed, Vickers and Zollman (1999) suggest that herbal medicines present the greatest risk of adverse effects of all the complementary therapies. They will thus form the core of the following discussion, and Ernst’s classification (1996b) will be used to structure this account (see Box 1).

Use of herbal remedies

The use of herbal remedies is common, with 35-45% of Americans using herbal products as medications (Cohen, 1998; Lee and Horne, 2001). In the UK spending on herbal products is now over £40 million a year (Vickers and Zollman, 1999). When 979 patients about to undergo surgery were asked about their use of herbal remedies and nutraceuticals (supplements not derived from plants), 170 (17.4%) reported taking such products (Larkin, 1999). The most frequently used herbs were ginkgo (Ginkgo biloba, 32.4%), ginseng (Panax and Eleutherococcus species, 26.5%), and garlic (Allium sativum, 26.5%).


Herbal remedies are plant-based, as in fact are many orthodox drugs - some 25% of present pharmaceutical preparations contain at least one active ingredient extracted from plant sources (Farnsworth, 1981). Moreover, thousands of our present drugs were originally derived from plants, including digitalis (foxglove), aspirin (willow and meadowsweet) and paclitaxel (Taxol) (Pacific yew).

However, in the case of orthodox drugs the active ingredient is isolated from the plant, chemically standardised, subjected to critical clinical assessment and then often replaced with a synthetic analogue (D’Arcy, 1991). In contrast, the herbalist uses mixtures of diverse herbal ingredients of varying potency.

Potency depends on the part of the plant used - for example root, stem, leaves or fruits - the time of the year it is picked, and the actual species of plant used: for example, ginseng may refer to many Panax and Eleutherococcus species (D’Arcy, 1993). Because potency refers to the amount of drug required to evoke a response, if the potency of the formulation of the herbal remedy is unknown it is difficult to know what dose to prescribe to get the desired effect without causing problems of toxicity.

An example of this problem is provided by mistletoe, the popular name for 1300 species of evergreen, including the European variety Viscum album. Mistletoe is used as an antispasmodic, diuretic and hypotensive, and some claim it has anti-cancer properties. Mistletoe extract contains at least three types of potentially toxic compounds: alkaloids - some of which may be cytotoxic - viscotoxins and lectins, which have haemagglutin and mitogenic actions (D’Arcy, 1991).

Adverse reactions

Modern drugs generally undergo extensive formal testing for therapeutic and adverse effects before being licensed. In this way drug regulatory bodies ensure that the risk of adverse effects is small and within acceptable limits.

No such controls exist for the majority of herbal remedies, however. They do not come under the aegis of the regulatory bodies and are not required to undergo systematic testing. Consequently our knowledge of their potential adverse effects and interactions is limited.

In the UK and the USA herbal remedies are considered as dietary supplements rather than as drugs. Consequently companies selling them cannot make any claims about their therapeutic effects and they give no advice about their adverse effects or contra-indications. Table 1 gives examples of some known medically serious adverse effects of herbal preparations.

Allergic reactions

Like orthodox drugs, herbal preparations can result in hypersensitivity reactions, which can range from dermatitis through to anaphylactic shock. For example, tea tree oil - widely used as a topical disinfectant - or camomile can cause allergic reactions (Knight and Hausen, 1994; Bossuyt and Dooms-Goossens, 1994).

Mutagenic reactions

Anthranoid laxatives such as aloe, cascara, rhubarb and senna have genotoxic potential and have been associated with colorectal cancer in epidemiological studies in humans (Ernst, 1996b). Chaparrel may also be mutagenic. One case has been described where a patient developed cystic renal cell carcinoma after regularly drinking Chaparrel tea (Smith et al, 1994).

Drug interactions

Most consumers believe herbal medicines are harmless, so they have no qualms with taking them in along with prescribed conventional medicines. In addition, many immigrants to the UK have their own traditional medicines, which they may combine with orthodox medical care (D’Arcy, 1993).

Both these practices can lead to harmful herb-drug interactions (Table 2). This problem is exacerbated because at least 30% of patients do not tell their doctor that they are using them (Eisenberg et al, 1993; Yoon and Horne, 2001). This is either because patients do not consider herbal remedies as ‘drugs’, and so when asked for a history of their medications do not mention them, or because they are reluctant to mention them for fear of a negative response from the practitioner. It is therefore vital that clinicians include questions about herbal remedies in their routine drug histories, and be informed rather than judgmental about their use.


Herbal medicines are not required to undergo the same quality checks as conventional drugs and so they may be contaminated or adulterated. For example, many Asian and Indian herbal remedies have been found to contain heavy metals such as lead, arsenic and mercury (Capriotti, 1999).

One of the worst examples of contamination causing adverse effects occurred in the USA in 1989, where there was an outbreak of eosinophilia-myalgia syndrome associated with the use of L-tryptophan, an over-the-counter dietary supplement used for weight loss (Anon, 1999). More than 1500 cases were reported, including 38 deaths. More than 95% of the cases were traced to an individual Japanese supplier. Researchers found some trace-level impurities, suggesting that a contaminated batch of L-tryptophan contributed to the outbreak.

False authentication

False authentication can occur inadvertently or deliberately. An example of this is Ginseng preparations. Only Asian ginseng contains the active compounds ginsenosides, but commercial preparations often do not make this clear (Ernst, 1996b).

More seriously, ingredients may be included which are not identified, including potent orthodox drugs such as digitalis, steroids, active oestrogens, phenacetin and glibenclamide (Ko, 1998; Beigel and Schoenfeld, 1998; Dunning et al, 2001).

Finally, one ingredient can be replaced with another. This led to an outbreak of fibrosing interstitial nephritis in Germany and France when ‘Guang fangi’ containing nephrotoxic aristolochic acids was substituted for the Chinese drug ‘Fangji’ (Arzneimittelkommission, 1994).


Herbal preparations have a role to play in modern medicine, and there is clear evidence of their therapeutic benefits (Barrett et al, 1999).

However, as with any therapy, herbal preparations have the potential to do harm as well as good. To prevent harm, nurses must be aware of the risks and benefits of herbal remedies. During admission procedures they must enquire about the herbal remedies the patient is using, together with prescribed orthodox drugs and over-the-counter medications.

Finally, they must be non-judgmental in their attitides to complementary therapies, accepting that patients have the choice to make their own decisions regarding treatment. The nurse’s role is to ensure that this is an informed decision.



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