Comfrey is a specific in the treatment of bronchitis and irritable, painful coughs, for it soothes inflamed tissue, reduces irritation and relieves congestion. But comfrey is a controversial herb and many health food stores no longer carry it. Comfrey contains a class of compounds that, when isolated and fed to laboratory rats in large doses, can cause liver damage.
For hundreds of years, Comfrey has been among the most widely used medicinal herbs in Europe and the United States with no adverse side effects ever reported. However, in 1984 a woman who had been taking comfrey-pepsin tablets developed liver toxicity and soon warnings of every description appeared in the media. Since then, three additional cases of liver disease have been found in people who took comfrey.
Because of the laboratory rat test results and because the FDA has published warnings about the herb based on these four cases, some herbalists no longer recommend comfrey. However, since none of the four human cases of liver disease were proved to be caused by comfrey and because thousands of tons of the herb have been consumed by hundreds of thousands of people with only good results reported, others continue to use it. A middle approach, which I share, is to substitute another herb in cases of liver disease but to recommend comfrey as part of an herbal therapy for lung diseases, bronchitis, asthma and other respiratory problems.