In November 1996, Arizona and California voters approved propositions that legalized the medical use of marijuana. According to proponents of these propositions, medicinal marijuana can effectively relieve some symptoms of AIDS, cancer, and other illnesses.

Indeed, many researchers and physicians maintain that marijuana alleviates the nausea, vomiting, and loss of appetite caused by AIDS and highly toxic drugs such as AZT. According to San Francisco writers Stephen LeBlanc and Jeff Getty, “Marijuana is medically necessary and beneficial for people with AIDS with wasting and nausea.” Furthermore, advocates of medicinal marijuana cite studies by the National Institute on Drug Abuse, Harvard University, and other groups describing the medical benefits of the drug.

But other observers contend that marijuana has little or no medical value and warn that its use can cause harmful side effects. In the words of New York University professor...