According to FBI data released yesterday, police arrested 1,663,582 people on drug charges in the United States last year, slightly fewer than the 1,702,537 arrested in 2008. A little more than half of the drug arrests involved marijuana, and nearly 9 out of 10 marijuana arrests involved possession, as opposed to sale or manufacturing. The number of marijuana arrests, 858,408, was up slightly from the previous year's total, 847,863, but still lower than the historic peak of 872,721 in 2007.
As I've noted before, there is no obvious relationship between marijuana arrests and marijuana use. Although arrests have more than doubled since the early 1990s, the number of pot smokers was no lower in 2008 than it was in 1990 and perhaps somewhat higher, even allowing for methodological changes that seem to have boosted self-reported drug use after 2001.