In response to public pressure to allow the medical use of marijuana, the Office of National Drug Control Policy, Washington, DC, funded a study by the Institute of Medicine evaluating the scientific evidence for benefits and risks of using marijuana as a medicine. The report used scientific reviews, public hearings, and reports from other agencies, and was evaluated by knowledgeable advisors and reviewers. It called for heavier investment in research on the biology of cannabinoid systems, careful clinical studies of cannabinoids in clinical syndromes, analysis of cannabinoids' psychological effects on symptoms, and evaluations of the health consequences of heavy marijuana use; recommends against the use of smoked marijuana in medicine and for the development of a medical cannabinoid inhaler; and recommends that compassionate use of marijuana be considered under carefully reviewed protocols. Finally, the report evaluates the abuse potential, tolerance, withdrawal, and gateway risks of medical use of cannabinoid drugs.