Although the US Food and Drug Administration (FDA) reviews and approves drugs for specific indications, the approval does not usually limit the use of those drugs in clinical practice. Indeed, prescribing for indications not reviewed by the FDA (“off-label”) is common. In a recent study of 160 frequently prescribed drugs,1 off-label use represented 21% of drug mentions, and 73% of these off-label uses had little or no scientific support. Off-label use has long been controversial because large numbers of patients may receive drugs that have had only limited testing for efficacy and safety, and some off-label uses may eventually be shown to have an unfavorable risk-benefit profile. High-profile examples include the use of the combination of fenfluramine and phentermine by millions of persons for weight loss and the widespread use of hormone therapy by postmenopausal women to prevent coronary artery disease.