The social costs of the marijuana laws are vast. There were 658,000 arrests for marijuana possession in 2012, according to F.B.I. figures, compared with 256,000 for cocaine, heroin and their derivatives. Even worse, the result is racist, falling disproportionately on young black men, ruining their lives and creating new generations of career criminals.

There is honest debate among scientists about the health effects of marijuana, but we believe that the evidence is overwhelming that addiction and dependence are relatively minor problems, especially compared with alcohol and tobacco. Moderate use of marijuana does not appear to pose a risk for otherwise healthy adults. Claims that marijuana is a gateway to more dangerous drugs are as fanciful as the “Reefer Madness” images of murder, rape and suicide.

There are legitimate concerns about marijuana on the development of adolescent brains. For that reason, we advocate the prohibition of sales to people under 21.