DOES IT WORK?:Comfrey is the name given to a group of related plants that grow all over Europe (the Symphytum species).
Comfrey root has been used traditionally in poultices, salves and liniments for external treatment of joint inflammation, bruises, sprains and arthritis. Sometimes a tea made from comfrey is used for stomach problems, diarrhoea and menstrual problems.
However, comfrey should never be taken internally or used on cuts or broken skin. Products for internal use are banned in Germany and Canada, and available in Ireland only on prescription.
Products for external use are available without prescription, but concerns are being raised about those also.
Problematic aspects
Comfrey contains a group of chemicals called pyrrolizidine alkaloids. These compounds are found in about 300 plant species around the world, although only some of them are used in herbal remedies.
In 1920, several cases of liver disease in South Africa were traced to pyrrolizidine alkaloids in a herbal remedy. Since then, outbreaks of liver disease have occurred in Jamaica, Afghanistan, India and elsewhere. These have been traced to various plants containing pyrrolizidine alkaloids which are now recognised as dangerous liver toxins. They cause the small blood vessels in the liver to collapse, leading to cirrhosis and eventually liver failure. Damage can occur after ingesting tiny amounts of the alkaloids over several weeks.
The damage can be irreversible and fatal if not caught in time.
Although comfrey contains pyrrolizidine alkaloids, the amounts vary from one part of the plant to another, by the time of the year and by the age of the plant.
Liver damage may develop very slowly, with the early symptoms being relatively commonplace like fatigue,
mild diarrhoea or blood in the stools. For this reason, the full extent of the problems caused by plants containing pyrrolizidine alkaloids is not known.
Evidence from studies
No controlled studies have been published on the oral use of comfrey. Given its well-established toxicity, it is unlikely any will be conducted for ethical reasons.
However, laboratory studies have demonstrated that comfrey contains other compounds which are effective in reducing inflammation and pain. A small number of randomised, controlled trials of comfrey ointments have been published recently.
In one study, almost 150 people with ankle sprains treated at German sports clinics used either comfrey ointment or a placebo ointment containing no medication. On all days over a week, those using the comfrey ointment had less pain, less swelling and greater mobility.
Another study at the same sports clinics randomly assigned more than 150 people with ankle sprains to either comfrey ointment or a commercial pharmaceutical gel (diclofenac). The two products were equally effective at reducing pain and swelling.
Another study with 220 patients with knee osteoarthritis assigned people to either comfrey ointment or placebo. Over three weeks, people using the comfrey ointment had significantly greater improvements in pain relief, knee mobility and quality of life.
In all these studies, no adverse effects were reported.
Recommendations
Comfrey should not be taken internally, even though it can be found in capsules and teas. Comfrey for oral consumption requires a prescription in Ireland, but even trace amounts can cause damage when ingested regularly.
Some evidence suggests that comfrey ointments are effective in relieving sprains and arthritic pain. However, other conventional and complementary ointments are also available that do not contain toxic components.
Some evidence suggests that the toxic compounds in comfrey ointments can be absorbed through the skin. Comfrey ointments should never be applied to cuts, open wounds or around the eyes or mouth.
When applied to unbroken skin, it should not be used for any longer than 10 days to avoid accumulation of the toxic compounds. If any generalised adverse effects develop, consult a GP and bring the ointment with you.
Women who are pregnant should not use comfrey ointments as pyrrolizidine alkaloids have caused birth defects in animals.
• Dónal O'Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University