Jacob Sullum

According to federal drug czar John Walters, the marijuana available in the United States is better than ever. Well, that's not quite the way he put it, but it's closer to the truth.

Last week, as part of its ongoing effort to convince baby boomers that today's "Pot 2.0" is much more dangerous than the stuff they smoked when they were young, Walters' Office of National Drug Control Policy (ONDCP) announced that "levels of THC -- the psychoactive ingredient in marijuana -- have reached the highest-ever amounts since scientific analysis of the drug began in the late 1970s." The University of Mississippi's Potency Monitoring Project reports that the average THC content of the seized marijuana it tests was 8.1 percent last year, up from 3.2 percent in 1983.

That increase is much less dramatic than the one Walters alleged a few years ago. In a 2002 San Francisco Chronicle op-ed piece, he asserted that "the potency of available marijuana has not merely doubled,' but increased as much as 30 times" since 1974, when "the average THC content of marijuana was less than 1 percent."

Since 1 percent is the threshold at which experimental subjects can detect a psychoactive effect, if Walters were right, it would mean that people who smoked pot in the mid-'70s, when marijuana was even more popular than it is today, typically did not get high as a result. This rather implausible claim is based on a small, nonrepresentative sample of low-quality marijuana that probably degraded in storage.

Worse, to get his impressive 30-to-1 ratio, Walters compared the weakest pot of the '70s to the strongest pot of this decade. As a review of research on marijuana potency in the July 2008 issue of the journal Addiction notes, "There is enormous variation in potency, within a given year, from sample to sample," such that "cannabis users may be exposed to greater variation of cannabis potency in a single year than over years or decades."

Even when the ONDCP is comparing annual averages, it's not clear that the government's samples, which depend on whose marijuana law enforcement agencies happen to seize, are comparable from year to year or representative of the U.S. market. Still, it's likely that average THC content has increased significantly during the last couple of decades as growers have become more adept at meeting the demands of increasingly discriminating consumers. The question is why Walters thinks that's a bad thing.

With stronger pot, people can smoke less to achieve the same effect, thereby reducing their exposure to combustion products, the most serious health risk associated with marijuana consumption. Yet the ONDCP inexplicably warns that higher THC levels could mean "an increased risk" of "respiratory problems."

Jacob Sullum

Jacob Sullum is a senior editor at Reason magazine and a contributing columnist on Townhall.com.
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