Back in 1986, Congress passed the Controlled Substance Analogue Enforcement Act, a law aimed at "designer drugs" that were similar to illegal compounds but different enough to escape prohibition. Nearly three decades later, the government is still scrambling to keep up with the output of creative underground chemists, banning one psychoactive substance after another, only to find substitutes already on the market.

Writing about a case the Supreme Court heard yesterday, Jacob Sullum says the analog drug law failed because it tried to do the impossible. It tried to stop people from achieving unsanctioned states of consciousness by banning chemicals based on criteria vague enough to cover unknown substances yet specific enough to give fair notice of which actions would lead to prosecution.