CU researchers find no correlation between cannabis and brain changes


One of the main cannabis prohibition memes these days is based around some recent studies that suggest that cannabis use produces physical changes in the brain. This one really caught fire after The Journal of Neuroscience published research last spring from a Harvard/Northwestern report that scanned the brains of 40 students, half who used cannabis and half who didn’t, and found volume, shape and density changes in two brain areas involved with emotion and motivation.

This got an enormous amount of press in publications no one should ever trust or read again like Time and USA Today, both of which seem to have become anti-marijuana mouthpieces. Media outlets greeted the Harvard study with the usual, scare-the-shit-outof-you headlines: USA Today came up with “Casual marijuana use linked to brain changes”; Time went even farther with “Recreational Pot Use Harmful to Young People’s Brains.”

Science being what it is, other researchers try to replicate results from other studies. To that end, Barbara J. Weiland, Rachel E. Thayer, Amithrupa Sabbineni, Angela D. Bryan and Kent Hutchison of the University of Colorado and Brendan E. Depue of the University of Kentucky looked at the brains of 158 individuals. They obtained high-resolution MRI scans from other studies and did their own investigations of differences in brain matter in the same regions.

Their report, “Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults,” was published in the same Journal of Neuroscience this year. It found no statistically significant differences between daily users and nonusers on volume or shape in the brain regions of interest. “The results indicate that, when carefully controlling for alcohol use, gender, age and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures.”

Whoa. Wait a minute. There are all these other studies. All those frightening headlines.

“Brain studies are difficult. When you look at the studies, one will find an effect in one region. The next group doesn’t find an effect there but finds a different effect. If you take one region across all studies, there’s no consistency,” says Hutchison, a member of the research team and the CU Department of Psychology and Neuroscience.

As it turns out, the brain is malleable. Stress can change it. So can depression and meditation.

“Learning to play a music instrument changes the brain,” Hutchison says. “It’s possible that a person may have a slightly different brain in the first place. Ultimately, we won’t be surprised to find out marijuana causes changes in the brain.”

Hutchison says there is plenty of work yet to be done, but that so far, none of the studies have proven that cannabis causes the brain changes, especially when alcohol use is factored in. He hopes a multi-year U.S. National Institute on Drug Abuse study that will examine the brains of 10,000 kids from before they begin using marijuana, tobacco and alcohol and follow them through the years will answer some of those questions.

Speaking of government studies, a recent one comes up with some surprising results for one of the vexing problems of legalization: What is the correlation between using cannabis and getting behind the wheel of a car?

Colorado and most states that are legalizing treat cannabis intoxication much as they do alcohol. Here if you are found to have five nanograms of THC per milliliter of blood, you can be considered impaired if you’re driving. Prohibition organizations scream bloody murder about stoned carnage on the highways while advocates argue that marijuana is less predictable and works far differently than alcohol, it’s much more difficult to test and many medical and regular users would test positive for five nanograms, whether they were impaired or not.

So the Department of Transportation’s National Highway Traffic Safety Administration’s comprehensive study of 3,000 drivers involved in accidents over a 20-month period was eagerly anticipated. It found that fewer people are drinking alcohol and driving and more people are driving under the influence of cannabis. The number of drivers with evidence of marijuana in their system grew by nearly 50 percent from 2007 to 2014.

For alcohol, the study not surprisingly found the crash risk for drivers with a blood-alcohol content of 0.08 percent was twice that for sober drivers, and the danger went up dramatically from there — up to 12 times as high for a 0.15 reading.

But the cannabis finding was quite different: THC-positive drivers were 25 percent more likely to be in an accident, but once the researchers adjusted for confounding variables like age, gender, race, demographics and alcohol use, they could find no more risk of a cannabis user causing an accident than someone who was completely straight.

This is a pretty astounding result and admission, especially for a government agency. It’s so interesting, in fact, that the official paper buries the info in favor of reporting that marijuana use is up rather than that its use was statistically not found to be a factor in accidents.

None of this is suggesting that people should be driving under the influence of marijuana — tests show it can impair driving ability. But what it does say is that perhaps the effects of cannabis are not as significant as those of alcohol, that cannabis doesn’t work in the body like alcohol and that we need better ways to study and approach the concept of cannabis impairment.

As far as I can find, neither USA Today nor Time covered the CU study. I did find the headline for the USA Today government driving survey: “Study finds new driving threat from dopers, druggies.”


You can hear Leland discuss his most recent column and Colorado cannabis issues each Thursday morning on KGNU.

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