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Side effects / toxicity of herbs.

Newsgroups: alt.folklore.herbs
Subject: Side effects/toxicity ReadMe First
From: jtreasure.jonno.demon.co.uk (Jonathan Treasure)
Date: 17 May 1995 13:53:03 +0100

Since there are fairly consistent posts to this group concerning safety and toxicity of herbal medicines, many of which are either misinformed, misleading or simply ignorant of the philosophy and practice of the subject of herbbal medicine, I have presumed to write some background notes which may be useful to those wishing to pursue these matters in more depth than possible with the usual Usenet banter....

Since the post is rather long, this is to warn all those not interested (newsreader software permitting) to not download the post whose Subject Header is Side Effects/toxicity .

Also please note the text does not offer a list of toxic herbs, but is a discussion of underlying issues from a western herbalist viewpoint.


jonathan treasure

From: jtreasure.jonno.demon.co.uk (Jonathan Treasure)

Introduction to side effects, safety and toxicity of medicinal herbs

by Jonathan Treasure http://www.herbological.com (included in the medicinal herbfaq).

This introduction concerns WESTERN medical herbs and their clinical use. Some herbal agents are common to different traditions but the indications and methods of use may vary between e.g. TCM, Ayurvedic and Western practices.

The purpose of these notes is to provide a general understanding of the actions of herbal medicines, and hence a background for understanding questions of safety and toxicity - NOT to provide a list of problematic herbs. A brief bibliography gives sources of reliable information on the safety of herbal medicine and further reading.

Conventional medicine considers that if a drug is to be effective, it will inevitably have side effects. The medical establishment considers herbal medicines as drugs, and as such, they must either have side effects - or ergo be ineffective.

Paradoxically tens of thousands of people every year turn to herbal medicine because they regard plant remedies as being free from undesirable side effects. Herbal medicines are considered to be generally safe AND effective agents.

Although there is a spectrum of viewpoints in western herbal medicine, most herbalists reject the view that plant medicines are naturally occurring analogues of the pharmaceuticals used in orthodox clinical medicine i.e. drugs.

This is ultimately a rejection of the dominant paradigm of orthodox clinical science. It is necessary to outline the elements of the alternative paradigm shared by most herbalists, before questions of toxicity and safety can be discussed in context of clinical herbal therapeutics, rather than of orthodox medical science

1 Medicinal plant actions cannot be reduced to the effects of their isolated 'active constituents'

There ARE a few plants that are almost "drug like" and whose action approaches that of pharmaceuticals. Digitalis is the classic example. Herbalists use these plants in near allopathic treatment strategies if at all, and in some countries e.g. UK, their availability is restricted by law. The number of herbs in this category is relatively few.

The vast majority of medicinal herbs contain dozens of different compounds, often of great complexity, mucilages, tannins, polysaccharides etc. that buffer, modulate and modify the effects of any "active principles". Study after study has shown that effects produced by extracts of whole plants cannot be mimicked by administering isolated purified constituents of the plant.

(It is ironic this proposition even has to be asserted given that biological sciences have for some time used a systems theory model in which the whole being greater than the sum of the parts is axiomatic - this simply reflects the inherent conservatism of the medical establishment. However for most herbalists the view of the whole being greater than the parts is derived from vitalism, not systems theory!)

2 Medicinal herbs act 'multi-systemically'

Pharmaceutical drugs are designed to elicit very specific reactions. Their associated "side effects" are undesired actions, usually traded as a "risk" against the "benefit" of the primary effect. Herbs tend to have several broad actions on a number of whole physiological systems at the same time. These actions are usually oriented in the same general therapeutic direction, and are usually complementary or synergistic, often non-specific, and very rarely adverse. Herb actions cannot be adequately described using the vocabulary of "drug" action terms, e.g. diuretic etc. - they are too complex. The clearest example of this is the coining of the term "adaptogenic " used to describe the multiple non-specific effects of herbs such as Ginseng.

3 Herbs act on the healing processes in the body

A pharmaceutical drug addresses symptoms caused by specific disease mechanisms as understood by scientific pathology. Herbal medicines are directed towards aiding the body's own healing processes. These approaches are diametrically opposed. Herbal medicines act gently, usually attempting to "nudge" or "support" systems and processes that have become deficient or help remove excesses that have become preponderant. Symptom relief is only a component of herbal therapeutic strategy.

This is a crucial difference. For example, serum arthritic conditions are conventionally treated with steroid anti-inflammatory drugs. These have widespread and disturbing side effects, which at sustained high doses become intolerable and potentially dangerous if not lethal. The herbal approach to these conditions uses dietary modification of metabolism; facilitation of elimination via kidneys and hepatic/ biliary routes; stimulation of circulation in the affected regions, moistening of dry synovia, etc. Topical treatments for acute joint pain or systemic anti-inflammatory herbs that help joint pain are used as required, but this is not the thrust of the treatment strategy. Lay persons often make the related mistake of seeking a "natural alternative" to a pharmaceutical they have been prescribed rather than challenging the diagnosis and therapeutic strategy.

4 Herbs act multi-dimensionally

Herbal medicine is a wholistic therapy, it integrates mental, emotional and spiritual levels seamlessly into its understanding of both human function and of the plant remedy, while respecting the planetary and ecological dimensions of natural medicine provided by plants. Although subject to differing interpretations this view is held in one form or another by most herbalists .

Life style, mental, emotional and spiritual considerations are part of any naturopathic approach, herbalism included. Flower essences, homeopathic preparations and drop doses of standard herb extracts all demonstrate that herbal agents can produce consistent and powerful effects at subtle levels in ways quite inexplicable by the pharmacokinetic model underlying orthodox pharmacology.

Centuries of medicinal plant usage overarch even the Graeco - Roman heritage of medical thought, itself already forgotten by its amnesiac infant technological medicine, extending into magical, esoteric and religious domains of prehistory. The great Asian systems of medicine have continued uninterrupted for thousands of years to today, integrated into profound cosmological and philosophical systems. From any serious study of the application of herbs to healing a perspective emerges that reveals modern doctors to be tragicomically "like educated peasants running around pretending to be chiefs" (Grossinger).

5 Side effects vs. contraindications

Many herbalists would tend toward the radical homeopathic view that the "side effects" of orthodox medicine are in fact iatrogenic developments of the very disease for which the pharmacological intervention was intended. The symptoms simply change, and the real underlying dysfunction is further obscured - or driven further into the interior to manifest in deeper and more intractable ways.

Notwithstanding this iatrogenic view of side effects, we have seen that the use of herbs anyway does not generally involve "drug" actions or adverse effects. Of course, if the body processes are nudged in the wrong direction for long enough, then imbalances can worsen rather than improve. Hence the need for informed knowledge of the effects of herbs as well as a clinical training to understand their appropriate medical application. Herbalists learn about the CONTRAINDICATIONS as well as the indications for using a herb. This term is more useful and appropriate than "side effects".

CONTRAINDICATIONS are incongruences between the metabolic/systemic predisposition (constitution) of the individual - and the spectrum of multi-systemic actions of a given herb agent or class of agents. Essentially, herbalists use their in depth knowledge to devise a mix'n'match prescription tailored precisely to fit an individuals unique profile. This approach is most sophisticated in the tonic energetics of the Oriental medical traditions, but is empirically applied by most herbalists.

Contraindicated remedies can account for apparently idiosyncratic "bad reactions" to a herb. Valerian is a classic example, its powerful autonomic effects can make it "disagree" with stressed adrenergically hyperactive individuals, who paradoxically are often those seeking sedative treatment for insomnia. Anyone experiencing such reactions to a herb for more than a couple of days should stop taking it and seek further advice. However a second and vital aspect of contraindications especially today is the question of DRUG INTERACTIONS.

Many people seeking herbal medical treatment are already involved in pharmaceutical therapies. Herbal remedies may act either as agonists or potentiate some drug therapies, and an understanding of conventional drugs is an essential prerequisite for effective herbal therapeutics. In many cases, herbalists would not treat the primary presenting symptom undergoing drug treatment - be it ulcers treated with Zantac or cardiac arrythmia treated with Digoxin - but rather concentrate on supporting other systems and functions stressed by the primary symptom. This allows the body to recover its strength and healing potential so it can then direct these capabilities toward repairing the presenting condition. In other cases, it can be a priority to wean someone off drugs, e.g. steroids, in which case supportive therapy to restore adrenal function is vital.

6 Safety and toxicity of herbal medicines

The definition of *toxic* is a ultimately a matter of viewpoint. Many ordinary foods contain constituents that could be regarded as poisonous, such as the alpha gliadin produced by gluten in wheat oats and rye, the cyanogenic glycosides in many fruit seeds, the thiocyanates of the brassica vegetables, alkaloids of the Solanaceae and lectins of many pulses including soya and red kidney beans. Nonetheless these foods are generally regarded as safe. Similarly, both water and oxygen - can kill in excessive amounts, so quantity is often an important consideration. In practice however, three groups of herbs can be identified from a safety point of view.

Firstly there are a handful of herbs that contain near pharmaceutical concentrations of poisonous constituents which should on no account be taken internally by unqualified persons except in homeopathic potencies. Examples are Atropa belladonna, Arnica spp, Aconitum spp, Digitalis spp. In many countries availability of these herbs is limited by law. Regulations vary from country to country and the appropriate regulatory authorities or Herb Organisations can be consulted for details. Wildcrafters should be unshakably confident in their identification of the local variants of these species, and children warned to avoid them. Fortunately this is a numerically tiny category.

Secondly, are herbs with powerful actions, often causing nausea or vomiting, (that usually were traditionally prized for this action). They are perfectly safe used under appropriate conditions. Some of these herbs are restricted in some countries but freely available in others. Lobelia and Eonymus spp are examples. There is some inconsistency here, for example Ephedra is restricted, perhaps with justification, in the UK, but is freely available in the US.

Finally, there is an idiosyncratic grouping of herbs which have been alleged, with some scientific support, to exhibit specific kinds of toxicity. The best known is the hepatotoxicity of pyrrolizidine-alkaloid-containing plants such as Comfrey (Symphytum). Other examples are Dryopteris (Male Fern), Viscum (Mistletoe) and Corynanthe (Yohimbe). Although much of the evidence is contentious (see below), lay users would be advised to avoid internal consumption of these herbs.

The vast majority of medical herbs are safe for consumption, but for those without specialised knowledge, it would be prudent to follow simple but sensible guidelines in self treatment:

  • Use only herbs recommended in respected herb books, especially in countries like the US where there are few restrictions on availability.
  • Avoid new or unproven *wonder remedies*.
  • Do not persist with a remedy if no benefit or result obtains after a moderate period, and if adverse reactions take place, stop the treatment and seek experienced advice.
  • Do not persist with a treatment that has brought improvement without testing to see if continued further consumption is necessary to maintain improvement.
  • Do not engage in self treatment for complex conditions without experienced advice. Drug interactions and contraindications must be considered on an individual basis and herbal treatment strategies are often involved and multifaceted.

Unfortunately, training and licensing of herbalists is not internationally consistent. In the US the situation is especially complex - no recognised herbal licensing exists. ND's are licensed in a few states, but their herbal training could theoretically be less than that of an unlicensed but experienced herbal practitioner. In the UK, the NIMH accredits herbalists who have trained at approved courses: practitioners are recognised by MNIMH or FNIMH qualifications.

7 Pregnancy

It is axiomatic that pregnancy should be a time of minimal medical intervention, and herbalists in particular regard pregnancy as a "contraindication" to taking herbal medicines. Nutritive "food herbs" such as nettle, and uterine tonics such as raspberry leaf are encouraged, and perhaps gentle treatments against typical symptoms such as constipation or morning sickness are in order. There is NO evidence of teratogenicity in humans arising from herbal remedies, but since such evidence would be hard to come by, erring on the side of caution is regarded as prudent.

8 Understanding toxicity research - politics and ideology

Medical orthodoxy at best does not understand herbal medicine, and at worst, sees it as a threat which it attempts to rubbish, regulate or ridicule. Quackery has a fascinating role in the history of medicine and its institutions, but much of the hostility towards herbal medicine comes from its apparently greater proximity to orthodoxy than say acupuncture or homeopathy. This is the unfortunate political context in which toxicity and safety of herbal medicines are debated.

Additionally, both professional herbalists and regulatory authorities exhibit differing degrees of education, organisation and aptitude in different countries. In the United States, the situation is particularly lamentable, with scare mongering stories regularly aired in medical, scientific and popular press, whilst the lack of accredited professional herbalist training means that well intentioned self-appointed spokespersons for herbalism can cause more harm than good, and the quixotic federal regulatory stance on herbs as foodstuffs means that the potential of lay self-iatrogenesis with freely available OTC herbal products is a serious possibility.

Toxicity of herbal medicines needs to be seen in context however. As Paul Bergner, Editor of the journal Medical Herbalism and author of several articles on herbal toxicity recently pointed out:

Approximately 8% of all hospital admissions in the U.S. are due to adverse reactions to synthetic drugs. That's a minimum of 2,000,000. At least 100,000 people a year die from them. That's just in the U.S., and that's a conservative estimate. That means at least three times as many people are killed in the U.S. by pharmaceutical drugs as are killed by drunken drivers. Thousands die each year from supposedly "safe" over-the-counter remedies. Deaths or hospitalizations due to herbs are so rare that they're hard to find. The U.S. National Poison Control Centers does not even have a category in their database for adverse reactions to herbs.

Similar figures apply in the United Kingdom, and even hepatoxicity, where perhaps the strongest case against some herbs lies, the statistics are horrendously clear - over 80% of cases of fulminant hepatic failure presenting for liver transplant (or death) over ten years in the UK were due to poisoning by freely available OTC non-prescription NSAID's, such as paracetomol and aspirin. Not one case was due to ingestion of medicinal herbs.

For the lay person, analysis of so called "scientific evidence" about toxicity is clearly problematic. Some of the most useful sources of information are to be found in review presentations made by representatives of the herbalist community to regulatory authorities such as the FDA or MCA. Informative reviews of the literature in defence of Comfrey and Mistletoe have been made in this way.

Herbalists justifiably point out that scientific studies with isolated compounds, on non human or even non mammalian organisms, or in vitro, with doses tens or even hundreds of times the equivalent medicinal dose, simply have no arguable extrapolation to the clinical situation using whole herb at appropriate medicinal doses.

Lack of herbal knowledge by some scientific investigators (let alone journalists or self appointed defenders of the public) leads to often ludicrously misleading results - one of the commonest mistakes being the failure to verify the actual identity of plant material used in their experiments, let alone the detection of contaminants!

These points beg the question of what paradigm can be used for research into the safety and efficacy of herbal therapies. That shibboleth of orthodoxy - the double blind placebo controlled clinical trial is open to a range of criticisms from the paradigm employed by herbalists - but that, as they say, is another story.

Further reading

Herbal/Medical contraindications:

  • Synergistic and Iatrogenic Potentials when some herbs are used concurrent with Medical Treatment or Medical Health Care by Michael Moore, 1995 , on line at http://www.swsbm.com

Herb information resource:

  • The Information Source book of Herbal Medicine: David Hoffmann, Crossing Press 1994. An excellent book.


  • Brinker F : An Introduction to the Toxicology of Common Botanical Medicnes, NCNM 1983
  • AMA Handbook of Poisonous and Injurious Plants AMA, Chicago 1985
  • NAPRALERT database at UIC.

Example reviews of problematic herbs:

  • In Defence of Comfrey: EJHM1.1.1994 11-17
  • The Case For Mistletoe EJHM1.1 1994 17-22
    (EJHM = European Journal of Herbal Medicine, http://www.ejhm.co.uk/)


  • Planet Medicine - Richard Grosssinger, North Atlantic Books 1990
  • The Magical Staff , Matthew Wood, North Atlantic Books, Berkely 1992

General herb books:

  • J.A. Duke, 1985. CRC Handbook of Medicinal Herbs, CRC Press.
  • C. Hobbs, (many booklets). Topics: Echinacea, Usnea, Medicinal Mushrooms, Natural Liver Therapy, Vitex, Milk Thistle, Immune Therapy. Botanica Press, Box 742, Capitola, CA 95010. (Most are $5- $10).
  • D. Hoffmann, 1988. The Herbal Handbook: A User's Guide to Medical Herbalism, Healing Arts Press. All texts by Hoffmann are reliable.
  • S. Mills, 1992. Out of the Earth: The Essential Book of Herbalism, Viking Press.
  • M.Moore, 1979. Medicinal Plants of the Mountains West, Uof NM Press.
  • M. Moore, 1990. Medicinal Plants of the Desert West, U of NM Press.
  • M. Moore, 1993. Medicinal Plants of the Pacific West, Red Crane Press.
  • R.F. Weiss, 1988. Herbal Medicine.

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