Jacob Sullum | June 1, 2009, 5:23pm

A few weeks ago, I noted the latest government report about ever-stronger marijuana. "According to the latest data on marijuana samples analyzed to date," the Office of National Drug Control Policy announced, "the average amount of THC in seized samples has reached a new high of 10.1 percent." But as Bruce Mirken of the Marijuana Policy Project notes, these samples included hashish (resin) and hash oil (extract), both concentrated forms of cannabis. The average for just marijuana (leaf and buds) was a substantially lower 8.5 percent, up from 8.1 percent in 2007. A New York Daily News article I quoted made the increase in average THC content look much bigger than that by comparing the 2008 number for marijuana plus hash (10.1 percent) to the 2007 number for what the ONDCP calls "marijuana seizures at Southwest border ports of entry" (7.3 percent).

As I mentioned in my earlier post, it's not clear how representative the samples seized and tested by the government are. Mirken notes that last year "the domestically produced marijuana tested tended to be significantly weaker than the imported stuff, but domestic cannabis only represented 29.7% of the samples tested." By contrast, a 2005 State Department report cited by Mirken suggests that domestic marijuana represents something like two-thirds of the U.S. market.

Regardless of exactly how much average marijuana potency has increased during the last two decades, of course, the government has yet to give a plausible reason for viewing the trend with alarm.

This year's marijuana potency report is here:
http://www.whitehousedrugpolicy.gov/...report_104.pdf