The US Congress voted this week to let the Food and Drug Administration regulate tobacco almost out of existence, but could not work up the nerve to ban it. The latest of America’s periodic bouts of prohibitionism is thus coming to an end in a typically ambivalent fashion. Authorities are split over whether people are moral agents, competent to make their own decisions about drugs, or helpless victims; and whether drug abuse is a choice or a disease.

In recent decades, the internal contradictions in US drug policy have been sharper than at any time since alcohol was banned after the first world war. Urban kids are sent to jail for drug possession while celebrities talk cheerily on television about beating their cocaine habits through rehab and self-help groups. We have a justice system that treats drug use as a malevolent act of will (to be punished) and a medical profession that treats it as an unfortunate disease (to be cured). Who is right? In a magnificent new book, Addiction: A Disorder of Choice , Gene M. Heyman, a lecturer in psychology at Harvard Medical School, argues that it is not his fellow medical professionals.