Herbs and related products are commonly used by patients who also seek conventional health care. All physicians, regardless of specialty or interest, care for patients who use products that are neither prescribed nor recommended. Some herbs have been extensively studied, but little is known about others. When a patient asks for advice regarding the use of a particular herb, how should a physician respond? Similarly, how does a physician determine if a patient's symptoms are caused by a "remedy"? This review attempts to answer these questions by investigating pertinent definitions, the history of herbs in medicine, epidemiology and prevalence of herbal use, and relevant psychosocial issues.