Toxic heavy metals and undeclared drugs in Asian herbal medicines.

Asian herbal medicines are currently used by large sections of the population. Because they are not regulated as medicines and are freely available to everyone, serious safety concerns might be associated with these herbal medicines. In this article, evidence suggesting that some Asian herbal medicines contain toxic heavy metals or undeclared prescription drugs is reviewed. In particular, Indian and Chinese preparations have been implicated. Although adulteration with drugs is by definition fraudulent, the inclusion of heavy metals could be either intentional for alleged medicinal purposes or accidental. Evidence from various countries implies that toxic heavy metals and undeclared prescription drugs in Asian herbal medicines might constitute a serious health problem. However, the majority of the data is anecdotal and insufficient to define prevalence figures. Ways ought to be found to maximize consumer safety.