Where’er you be
Don’t drink comfree
For drinking such tea
Could be the death of thee!
John R. L. Walker
Our everyday “cuppa” comes from the plant Camellia sinensis and it, together with a number of other common drinks including coffee, cocoa, guarana and maté contain small quantities (10-100 mg per cup) of caffeine, a mildly stimulatory alkaloid. In addition many people enjoy hot and cold beverages made from a wide variety of other herbs such as chamomile and dried raspberry leaves.
Unfortunately, an uncritical mythology has developed regarding herbal teas made from other plants that maybe very dangerous. Notable among these are herbal teas made from comfrey, coltsfoot and sassafras; the former contain toxic alkaloids while the latter contains the carcinogen safrole. Recently, the German government’s health authority, the Bundesgesundheitampt (BGA), has decided to ban some fifty herbal and homeopathic remedies because they are ineffective or contain toxic alkaloids. High on their list is comfrey.
They comment that although a medicament is derived from a common plant, it can be just as dangerous as any laboratory-synthesised chemical. This fact has been well known since the death of Socrates from a dose of hemlock (which contains the alkaloid coniine), but is all too often conveniently ignored by the herbal mystics.
Here in New Zealand there are many recorded animal deaths from ingestion of tutu (Coraria arborea) which contains “tutin”, a poisonous picrotoxinin.
Comfrey (Symphytum officinale) has aquired an almost magical status in herbal medicine, comparable almost to that of ginseng. It is one of the most often sold herbal remedies. However, unlike ginseng, comfrey has been shown to contain highly toxic alkaloids, yet many modern herbalists still wax lyrical about its safety and almost universal healing properties.
Comfrey is frequently used in folk medicine as an externally applied poultice for wound healing, and such treatments may be useful since comfrey contains allantoin, which promotes cell proliferation, tannins and mucilage.
So far so good, but comfrey is also recommended by many herbalists to be taken internally as a “blood purifier” and as a universal panacea for numerous other ailments including respiratory complaints and ulcers of the bowels, stomach, liver or gall bladder.
Now, in the light of much well-documented research, the German BGA has banned the sale of herbal remedies containing comfrey. This is because comfrey contains a group of chemicals known as the pyrrolizidine alkaloids which have been shown to be carcinogenic and to cause severe, even fatal, damage to the liver.
Coltsfoot (Tussilago farfara) and Senecio species, such as groundsel, are other common herbal remedies which also contain these dangerous pyrrolizidine alkaloids, although for many years coltsfoot has been prescribed as an ingredient of herbal cough syrups and smoking mixtures. Japanese and other research workers have shown that these preparations may be potential causes of liver damage.
Problems with herbal remedies nay also arise from other causes such as adulteration, contamination and misidentification. The latter should be of major concern since, for most herbal products, there is no guarantee that the original plant(s) were unequivocally identified by a competent botanist.
As with any drug, susceptibility to poisoning varies between individuals and may be affected by gender, age and state of health. in a recent paper Dr Ryan J. Huxtable comments that, in North America, more people are killed or injured by plant derived substances than by animals. Yet, despite this, the US herbal industry is still virtually unregulated and without legal safeguards to demonstrate the safety or efficacy of its products.
Locally sourced herbal teas from New Zealand native plants are now becoming available, but we should remember that many of our native plants produce alkaloids and other toxins which are dangerous if ingested. I therefore caution anyone who buys a herbal beverage to require not only a list of its plant components but also to be sure that these plants were competently identified.
For the edification of readers I append a list of a few common poisonous plants found in New Zealand and which I would not want in “my cup of tea”.
Common Poisonous Plants |
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| Plant | Botanical Name | Toxic Principle |
| Apricot (kernals) | Persea armeniaca | Cyanogenic glycosides |
| Bittersweet | Solanum dulcamara | Alkaloids |
| Foxglove | Digitalis purpurea | Steroidal glycosides |
| Hellebore | Helleborus sp | Steroidal glycosides |
| Karaka (fruit) | Cornyocarpus laevigatus | Cyanogenic glycosides |
| Kowhai | Sophora sp | Alkaloids |
| Ngaio | Myoporum laetum | Ngaione |
| Peach (kernals) | Prunus persica | Cyanogenic glycosides |
| Porporo | solanum aviculare | steroidal glycoalkaloids |
| Ragworts | Senecio sp | Pyrrolizidine alkaloids |
| Tutu | Coraria sp | Tutin |
Bibliography
Connor, H.E. The Poisonous Plants in New Zealand. (1977) Govt Printer, Wgtn.
Huxtable, R.J. (1992) The Myth of Benificent Natue; the risks of herbal preparations. Annals of Internal Medicine 117; 165-166.
Stewart, J. Plants in New Zealand Poisonous to Man. (1975) Govt Printer, Wgtn.
Tyler, V.E. The New Honest Herbal (1987) George F Stickley Co. Philadelphia. (Highly recommended).
