How physicians should evaluate dietary supplements.

Dietary supplements occupy a unique niche within the realm of modern medicine. These products are often used by patients at their own discretion, in an unmonitored setting, and without the input of their physicians. Although laws pertaining to dietary supplement labeling prohibit specific claims for the treatment or prevention of disease, these products are widely used as "alternative" or "complementary" therapy. Dietary supplements are readily available, not classified as over-the-counter medications, and not regulated as such. Patients and providers alike often assume these products are at least safe and possibly effective. Historically, dietary supplement pharmacodynamic and pharmacokinetic data have been limited and of meager quality. Information on dietary supplements in nonmedical literature is typically unreliable, and even in the medical literature, numerous studies have used products that were not well characterized. Although greater attention has recently focused on dietary supplement quality and integrity, complex issues persist and must be addressed when evaluating literature and advising patients. We seek to clarify many of these issues and make practical suggestions for the clinician.