In recent years the use of herbal remedies has increased in western society, bringing withit an increase in the risk and frequency of adverse effects and interactions with conventional prescription and proprietary medications. Problems asociated with herbal remedies include lack of quality control, lack of government regulations regarding safety and efficacy, a paucity of clinical trials and inadequate information on adverse effects and drug-herbal interactions. This article discusses these problems in the context the historical evolution of botanical-source medications and reviews problems associated with specific herbals including those with serious toxicity such as ephedra, borage, coltsfoot and calamus, as well as those with demonstrated interactions with conventional drugs such as St. John's wort. Mechanisms are discussed where known. Some two dozen individual herbs are tabulated with respect to their traditional use, pharmacological activity and potential for interactions. The potential for herbal remedies to serve as a source for new prescription drugs is also discussed.