THE American criminal justice system now spends a significant proportion of its resources enforcing the drug laws. More than 10 percent of all arrests and about 20 percent of all incarcerations involve drug law violations. (Most of the 1.5 million annual drug arrests are for simple possession, while the majority of the 325,000 people behind bars on drug charges are there for dealing.) Drug-related arrests are up 50 percent over the past 10 years, and drug-related incarceration is up 80 percent. And the burden of drug law enforcement falls especially on urban minority communities: Will Brownsberger and Anne Morrison Piehl of Harvard found that the poorest neighborhoods in Massachusetts, with a little more than 10 percent of the state’s population, accounted for 57 percent of state prison commitments for drug offenses, while Peter Reuter and his colleagues at RAND estimated that nearly a third of African-American males born in the District of Columbia in the 1960s were charged with selling drugs between the ages of 18 and 24.