Dumb Hidden Assumptions in Drug Abuse Research - An Update

And do not forget the private prison system and racist people in positions of power who want to ruin the lives of as many African-American youths as possible.

In my post of November 21, 2014, I reported on a study that showed that regular adolescent marijuana use was associated with a reduced likelihood of finishing high school, among other things. The authors of the study attributed these results to marijuana essentially causing brain damage, rather than to the fact the kids who feel the need to get stoned all the time have other problems which could easily account for their poor performance. Almost none of these other problems were controlled for in the study.

I asked, "What on earth makes people who draw the conclusion that the drug was the primary cause of the lower achievement become so stupid that they don't see that frequent drug use is a sign that the teens already had emotional problems before they even started smoking - and that it was these problems that predate the drug use that were the real cause of both the drug use AND the poor performance?"

Well guess what? Two new studies show exactly what I was talking about.

First was a new, ongoing study funded by the U.K. Medical Research Council, the Welcome Trust, and the University of Bristol, whose authors had no financial conflicts of interest. It's key clinical point: Previous research findings showing poorer cognitive performance in cannabis users may have resulted from the lifestyle, behavior, and personal history typically associated with cannabis use rather than the cannabis use itself.

Occasional to moderate cannabis use at a young age was not found to be associated with detrimental effects on cognition or educational performance. It was true that adolescents with heavier use – defined in the study as self-reported lifetime use of cannabis 50 times or more by age 15 – had a modest 2.9% decrease in educational performance on a compulsory school exam given at age 15 or 16, compared with never-users. However, heavier use had no impact at all on IQ scores measured at age 15 after adjustment for potential confounding factors.

"Previous research findings showing poorer cognitive performance in cannabis users may have resulted from the lifestyle, behavior, and personal history typically associated with cannabis use rather than cannabis use itself,” said Claire Mokrysz, of University College London.

She reported on 2,612 children who had their IQ tested at ages 8 and 15. Adolescents with heavier cannabis use by age 15 had a nearly a 3-point lower IQ at that age than did never-users, after adjustment for IQ at age 8. However, upon further adjustment for maternal education, pregnancy, and early-life factors, and use of tobacco, alcohol, and other recreational drugs, the difference in IQ between heavier and never-users vanished.

Heavier users of cannabis scored an initially impressive 11% lower than never-users on the standardized educational performance exam in an unadjusted analysis. After adjustment for the potential confounders, however, the difference shrank to a modest 2.9%. 

Performance, by the way, is not the same thing as ability. Even in this study, no effort was made to control for the motivation of test subjects, or for whether they were being distracted by ongoing problems such as family chaos at home.

The authors added that the belief that cannabis is particularly harmful may detract focus from and awareness of other potentially harmful behaviors. Not to mention other more important psychological and family issues.

The second study was done by neuroscientists at the University of Colorado at Boulder and published January 28, 2015 in the Journal of Neuroscience. Its major finding: Daily marijuana use is not associated with brain shrinkage when using a like-for-like method to control for the effects of alcohol consumption on those who both drink and toke up.

Kent Hutchison, a clinical neuroscientist at the University of Colorado, Boulder, and the senior author of the study, said his team reviewed a number of scientific papers that showed marijuana causes different parts of the brain to shrink, and his team found the studies were not consistent.

"So far, there's not a lot of evidence to suggest that you have these gross volume changes" in the brain, Hutchison said. 

I wonder how often Nora Volkow and other leaders of the National Institute on Drug Abuse will discuss these two studies or even mention them in their public presentations opposing marijuana legalization. Probable answer: NEVER.