American taxpayers are now spending more than a billion dollars per year to incarcerate its citizens for pot. That's according to statistics recently released by the U.S. Department of Justice's Bureau of Justice Statistics.

According to the new BJS report, "Drug Use and Dependence, State and Federal Prisoners, 2004," 12.7 percent of state inmates and 12.4 percent of federal inmates incarcerated for drug violations are serving time for marijuana offenses. Combining these percentages with separate U.S. Department of Justice statistics on the total number of state and federal drug prisoners suggests that there are now about 33,655 state inmates and 10,785 federal inmates behind bars for marijuana offenses. The report failed to include estimates on the percentage of inmates incarcerated in county and/or local jails for pot-related offenses.

Multiplying these totals by U.S. DOJ prison expenditure data reveals that taxpayers are spending more than $1 billion annually to imprison pot offenders.

The new report is noteworthy because it undermines the common claim from law enforcement officers and bureaucrats, specifically White House drug czar John Walters, that few, if any, Americans are incarcerated for marijuana-related offenses. In reality, nearly 1 out of 8 U.S. drug prisoners are locked up for pot.

Of course, several hundred thousand more Americans are arrested each year for violating marijuana laws, costing taxpayers another $8 billion dollars annually in criminal justice costs.

According to the most recent figures available from the FBI, police arrested an estimated 786,545 people on marijuana charges in 2005 -- more than twice the number of Americans arrested just 12 years ago. Among those arrested, about 88 percent -- some 696,074 Americans -- were charged with possession only. The remaining 90,471 individuals were charged with "sale/manufacture," a category that includes all cultivation offenses, even those where the marijuana was being grown for personal or medical use.

These totals are the highest ever recorded by the FBI, and make up 42.6 percent of all drug arrests in the United States. Nevertheless, self-reported pot use by adults, as well as the ready availability of marijuana on the black market, remains virtually unchanged.

Marijuana isn't a harmless substance, and those who argue for a change in the drug's legal status do not claim it to be. However, pot's relative risks to the user and society are arguably fewer than those of alcohol and tobacco, and they do not warrant the expenses associated with targeting, arresting and prosecuting hundreds of thousands of Americans every year.

According to federal statistics, about 94 million Americans -- that's 40 percent of the U.S. population age 12 or older -- self-identify as having used cannabis at some point in their lives, and relatively few acknowledge having suffered significant deleterious health effects due to their use. America's public policies should reflect this reality, not deny it. It makes no sense to continue to treat nearly half of all Americans as criminals.