Study: Smoking weed probably didn't make you stupid

Smoking this will not make you stupid. Smoking this and watching <i>Three's Company</i> reruns might.

Smoking this will not make you stupid. Smoking this and watching Three's Company reruns might.

Anecdotal evidence indicates marijuana use can lead to short-term confusion. Was it Gary Busey who played Buddy Holly? Or one of the Quaid brothers? How many Quaid brothers are there? Isn't one of them dead? 

But the long-term effects of America's leading recreational drug are still up in the air.  

A new study out from a group of researchers at the University of Minnesota and teams from two California schools casts doubt on the widely held belief that pot contributes to IQ loss in adolescents. It also creates a serious challenge to recent research that had found a causal link between rolling joints and losing points. 

The study, published in the current issue of the Proceedings of the National Academy of Sciences, breaks ground by studying twin siblings instead of individual subjects. This gave the scientists a "control" group of twins who were exposed to the same environment, even lived in the same homes. In this instance: California or Minnesota teenagers who like to get high. The paper assessed about 600 sets of twins in California and two pools, each numbering 1,000 or more, who grew up here. 

The kids were under intermittent study for years at a time, and submitted to IQ-like testing throughout. Marijuana use was calculated on the honor system, with subjects asked if they had ever smoked, and if so, how often. One finding of note: Some 60 percent (!) of the Cali kids admitted they'd used, compared to 36 percent of the twins from Minnesota, though subjects local to us were a couple years younger at the time they were under observation.

About one in five of those who said they smoked reported getting high on a daily basis.

Next study proposal: How high do you need to be to watch the Matrix again?

Next study proposal: How high do you need to be to watch the Matrix again?

The bad news: Kids who smoked were, indeed, losing IQ points.

The less-bad news: That IQ drop didn't change much between teens who had experimented a few times and those who became daily users. 

The surprising news: The twin siblings of smokers who abstained completely from marijuana experienced similar declines, and in some cases even greater losses, on tests of intelligence. Performance by smoking and nonsmoking twin teens was not statistically different on "Vocabulary," "Information," "Block Design," or "Matrix Reasoning," which we assume measures one's ability to explain the movie The Matrix.

The researchers are quick to point out that the study doesn't mean you should buy a bong for your 13-year-old. (He should get a damn job and buy his own.) Indeed, in an email response, Nickolas Jackson, a UCLA researcher who co-authored the paper with the U of M's Joshua Isen, seemed annoyed by coverage that proclaimed marijuana is A-okay for people to indulge as much as they'd like.

But it's just plain wrong, Jackson wrote, to say a kid's IQ has dropped because she started smoking, when her nonsmoking twin sister comes out of her teen years with roughly the same IQ trend. More likely other factors — genetic, educational, or related to the home environment — brought them down. 

It won't be easy to expand on the study, because marijuana research is literally harder to get approved than heroin. Marijuana's the only drug that faces a stringent review, without timetable, from the Public Health Service before studies can get approved. Consider that a drug 20 million Americans admit to using in the past month can't get studied, because it's just too dangerous and scary. Now who seems paranoid?