Marijuana Potency Hype: Is Fact-Checking Dead?

May 29, 2009

drug czar, marijuana, potency, science

In mid-May, spurred by a press release from the drug czar's office, the American news media reported with varying levels of hysteria that average marijuana potency had soared past the 10% THC level for the first time. Clearly the sky was falling, or at least was about to.

Small problem: According to the actual report, from the Marijuana Potency Monitoring Project at the University of Mississippi, average marijuana potency is only 8.52% -- a fact easily determined by doing something most journalists apparently didn't bother to attempt: reading the report, which is based on tests of samples seized by police. The way they got to the claimed rate of 10.1% was by including samples of hashish (average potency 20.76%) and hash oil (15.64%).

There's more. While the potency of marijuana samples did increase a bit from the comparable period a year ago, the overall proportion of samples represented by hash and hash oil also increased. That is, a greater percentage of the cannabis products seized and sent in for testing was the high-strength stuff.

But are these police seizure samples tested representative of what's actually available to marijuana consumers? There is absolutely no way to be sure, but every indication is that they aren't.

First, the number of samples tested dropped markedly, from 1290 a year ago to 818 in the current period. Why such a big drop? The MPMP report doesn't say.

Second, as with prior years, 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. No one seriously believes that less than a third of the marijuana consumed in the U.S. is produced here. Indeed, a 2005 State Department report suggests that the real proportion is almost the exact reverse: "More than 10,000 metric tons of domestic marijuana and more than 5,000 metric tons of marijuana cultivated and harvested in Mexico and Canada is marketed to more than 20 million users in the United States. Colombia, Jamaica, and Paraguay also export marijuana to the U.S.” Those last three countries, though, represent a tiny fraction of what comes here from Mexico and Canada.

Is the average potency of marijuana inching upward? Probably, though there isn't the slightest evidence that this makes it more dangerous. Is the real average potency over 10%? Only if you believe in the tooth fairy.