Drug policy has been an inconvenient issue for the national security apparatus of the United States, whether run by a Democratic or Republican administration. Even after 35 years of some sort of domestic “war on drugs”, forcefully articulated by every President since Ronald Reagan, the international dimension of the issue remains distasteful to diplomats. It often involves dealing with law enforcement in corrupt countries and complicates many a U.S. Ambassador’s life. The contending lobbies that care about it are loud, moralistic and well informed. If that were not enough, most of our principal allies, particularly in Europe, think there is a certain madness in the American belief that international interventions against the drug trade can accomplish much good.

Mere inconvenience is an insufficient reason to abandon a policy, of course, but in this case there are stronger arguments for change. The Obama Administration has an opportunity before it, for both history and argument show that U.S. international efforts to control drug production and trafficking cannot do much more than affect where and how coca and opium poppies are grown. The quantity produced is minimally affected, since suppression of production in one country almost invariably leads to expansion in another.

More important, control efforts often cause damage. Not only are such programs as spraying poppy and coca fields themselves harmful, but forcing the drug trade to move from one country to another may hurt the new producer country more than it helps the old one. Hence, the U.S. government should no longer push for “global containment”, as the policy has been defined. Rather, it should focus attention and resources on supporting the few states both willing and able to do something about production or trafficking in their countries. Unfortunately, Afghanistan, the center of attention right now, is not one of those countries.

The United States has been the principal driver of international drug control efforts since 1909, when it convened a meeting of the International Opium Commission (primarily aimed at helping China cut its opium consumption). The United States then pushed for the creation of a web of prohibitionist international treaties under the auspices first of the League of Nations and then the United Nations. Its voice is the dominant one at the annual meetings of the UN Commission on Narcotic Drugs. In that forum it has stood firm against any softening of existing policies. Most prominently, the United States has denounced in recent years “harm reduction” interventions such as needle-distribution programs aimed at reducing the spread of HIV.

Nor does it hesitate to scold even its closest neighbors for deviating from its hard-line, prohibitionist stance. In 2003, U.S....