In recent years, several states have passed or narrowly defeated referendums legalizing the use of marijuana for medical purposes. In 1996, Arizona and California became the first states to pass such laws. In 1998, Alaska, Nevada, Oregon, and Washington passed their own medical marijuana initiatives, and voters in Arizona chose to validate their 1996 decision. Polls suggest that voters in Colorado and the District of Columbia approved similar measures in 1998; however, the Colorado initiative was invalidated by the secretary of state, and the D.C. vote was never counted due to Congress’s refusal to fund the certification process. These events have further intensified an already heated debate over the legalization of marijuana as medicine.

Proponents of medical marijuana insist that the drug is beneficial in the treatment of many disorders—especially chemotherapy-induced nausea and AIDS wasting syndrome, but also glaucoma, pain, and...