On Thursday night's edition of "Anderson Cooper 360," former drug czar John Walters and I were interviewed separately about a new government report claiming an increase in average potency of marijuana seized by law enforcement (we'll have a video link posted soon). I pointed out an obvious fact: When the marijuana is more potent, users smoke less, just as people typically drink a much smaller quantity of bourbon than of beer. Thus, higher-potency marijuana doesn't necessarily mean users take in more THC. And, given that the most significant health issue connected to marijuana is the respiratory harm from smoke, smoking less to get the same effect is clearly healthier.
Asked about this, Walters said flatly, "There is no evidence of that."
He lied. I know this won't be a huge shock to faithful readers of this blog, but I think it's worth putting the facts on the record.
In a study titled "Vaporization as a Smokeless Cannabis Delivery System: A Pilot Study," published in May 2007 by the journal Clinical Pharmacology and Therapeutics, University of California researchers looked at smoking and vaporization using marijuana of 1.7%, 3.4% and 6.8% THC. Because the idea of the study was to compare smoking and vaporization, participants were guided through a standardized puff procedure.
Although the high-strength marijuana was four times as potent as the weakest, it produced a peak plasma THC level only about 20% higher, smoked or vaporized. This, the researchers wrote, suggests that either less is absorbed at the higher potency levels or there is "self-titration of THC intake," meaning that "smokers adapt their smoking behavior to obtain desired levels of THC." Among the evidence for self-titration, researchers found that their subjects tended "to take more puffs at lower THC concentrations" -- despite having been given a fairly regimented smoking procedure to follow. Similarly, the subjective "high" reported by participants was only modestly more intense at 6.8% THC than at 1.7%.
Prohibitionists are entitled to their own opinions. They aren't entitled to invent their own facts.
One final note: I was disappointed that perhaps the most important thing I said to the interviewer didn't get on the air. If potency is a concern, there is an obvious solution: Regulate marijuana as we do alcoholic beverages, and require the cannabinoid levels to be listed on the label. If consumers know what they're getting -- as they do now with beer, wine, or Bacardi 151 -- they can adjust their behavior to avoid unpleasant surprises.