The FDA recently advised health care professionals and consumers not to use a number of dietary supplements found to contain the phosphodiesterase-5 inhibitor sildenafil (Viagra) or an analog of the drug (www.fda.gov). Although the effects of sildenafil may be noticeable (in men), the presence of other, possibly more toxic adulterants in dietary supplements may be more difficult or impossible to detect.

Other drugs previously found in dietary supplements have included lovastatin (Mevacor, and others), estrogen, alprazolam (Xanax, and others), indomethacin (Indocin, and others) and warfarin (Coumadin, and others). Aristolochic acid in Chinese herbal weight loss products caused acute renal failure in about 100 women in Belgium; at least 70 of them required dialysis or transplantation, and at least 18 developed urothelial cancer (Med Lett Drugs Ther 2002; 44:84).

Dietary supplements do not require FDA approval before marketing. The agency does have the power to remove mislabeled or adulterated products from store shelves, but the burden of discovery and proof is entirely on the government.

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Millions of people now take herbal products and other "dietary supplements." The Physicians' Desk Reference has published a PDR for Herbal Medicines listing their ingredients and indications, and the Drug Topics Red Book lists their prices.