The classification of cannabis as a schedule one narcotic is among the least defensible aspects of prohibition.

Dr. Jody Corey-Bloom, director of the Multiple Sclerosis Center at UC San Diego, recently helped run a study that provided multiple sclerosis patients with either a marijuana joint or a placebo that looked, smelled, and tasted like marijuana. After smoking whichever substance they were given, patients were tested to see if it reduced their muscle spasticity — an affliction, common to MS patients, that causes painful, uncontrollable spasms of the extremities. Spasticity was unaffected among the placebo patients but dropped 30 percent on average among the patients given real marijuana. The side effects? “Smoking caused fatigue and dizziness in some users,” says Reuters, “and slowed down people’s mental skills soon after they used marijuana.”

The UC San Diego study is just the latest to suggest that marijuana has some medical benefits. Sixteen states, thousands of doctors, and tens of thousands of sick people concur in that judgment. It is dramatized by the personal testimony of sick people who are offered much more powerful drugs, but nevertheless insist that consuming marijuana was most effective at helping them.

Marijuana is nevertheless classified under the Controlled Substances Act as a Schedule One drug…