The goal of most treatment programs is to get addicts off drugs— and to keep them that way. Disagreement persists over whether treatment programs have lasting results, with critics pointing out that even addicts who desperately want to quit often relapse. Even more difficult is the challenge of treating drug addicts who do not wish to quit. Heroin addicts, for example, often resist treatment because they fear the excruciating withdrawal symptoms that come with quitting heroin.

One response to the difficulty of treating resistant addicts is harm reduction programs—programs that aim to reduce the social costs of drug addiction, such as crime and the spread of disease through shared needles. The most widely implemented harm reduction measure is needle exchange programs, which allow addicts to trade used syringes for clean ones. Another, more controversial approach involves administering legal, low-...