FAQ / Is comfrey toxic?

Comfrey, along with coltsfoot, contains pyrrolizidine alkaloids, chemicals that can cause liver toxicity if taken in huge amounts. Some herbalists recommend against using these herbs. Although we disagree, you should make your own mind up about these controversial herbs. One bit of data that you might be interested in is a study done by noted biochemist Bruce Ames, PhD of the University of California at Berkeley. His data states that a cup of comfrey leaf tea is less carcinogenic than an equal amount of beer.

The problem is two-fold: firstly there are two "comfreys" and reference to them is often casual. Regular, common, medicinal comfrey is Symphytum officinale. Russian comfrey, the great compost heap maker, is Symphytum x uplandicum. Medical herbalists in the UK, from whose written reports I am extrapolating, point out that Russian comfrey was probably the herb used in the toxicity trials yet regular comfrey is also restricted or banned.

Secondly, when the toxicity tests were done in the late 70s, a chemical constituent called pyrrolizidine alkaloid was isolated, extracted from leaves & injected into baby rats at what many medical herbalists consider an "unrealistic level". In other words far more comfrey than a human would eat to get such a toxic level of . Also baby rats are smaller than humans; they do not have the same metabolism as humans; and an isolated chemical injected outside the rat's stomach wall is not the same as a human eating leaves with many chemical constituents and digesting them normally. A chemical in isolation will cause different reactions from a group of chemical constituents containing that one as well

There are four cases involving humans which do implicate comfrey. One involved a woman who was finally diagnosed as having veno-occlusive disease & did consume a quart of herbal tea/per day that contained comfrey. A second case involved a boy with Crohns disease who was treated with conventional medicine for some time before going over to comfrey root & acupuncture. The long running malnutrition may have weaken the liver predisposing it to the venal obstruction problem. Comfrey root was blamed. The drugs were not considered as possibilities. The third case involves a woman who overdosed: 10 cups of comfrey tea a day & handsful of comfrey pills. After 9 years, she had serious liver problems. The fourth case became a fatality. A vegetarian, given to specific food binges for weeks, took an unknown amount of comfrey for flu like symptoms possibly over a period of four months. The particulars of his case are blurred. All cases involve comfrey; in at least three, there are suggestions of overdose or abuse of the plant. WHICH plant, I don't know.

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