The bad effects of high-potency weed are no longer just reefer madness hype.
By May Wilkerson Monday, November 30th, 2015
The claims that marijuana can lead to brain damage have often been dismissed by pot advocates as “reefer madness.” But scientists now claim that, while regular marijuana may be benign, high-strength marijuana could damage nerve fibers that help transmit messages across the two halves of your brain.
In the first study to examine the effects of marijuana potency on brain structure, researchers examined brain scans of people who regularly smoked “skunk” and found “subtle differences” in the white matter that carries signals between the left and right hemispheres of the brain. These changes were not seen in people who had smoked less potent marijuana, or those who had not used marijuana at all, researchers found. The findings suggest that long-term use of high-potency weed could make brain communication “less efficient.”
Researcher Paola Dazzan, a neurobiologist at the Institute of Psychiatry at King’s College London, said these effects seem to be linked to the level of THC. Traditional marijuana buds contain 2% to 4% THC, whereas the more potent varieties can contain 10% to 14% THC.
Whether or not a person actually experiences psychosis, high levels of THC seemed to impact the corpus callosum area of the brain. The scans found that daily users of high-potency marijuana had a slightly greater “mean diffusivity” of about 2% in the corpus callosum. “That reflects a problem in the white matter that ultimately makes it less efficient,” said Dazzan. “We don’t know exactly what it means for the person, but it suggests there is less efficient transfer of information.”
However, though the findings indicate a link between high levels of THC and damage to white matter, researchers could not confirm that THC caused the damage. “It is possible that these people already have a different brain and they are more likely to use cannabis,” Dazzan noted. “But what we can say is if it’s high potency, and if you smoke frequently, your brain is different from the brain of someone who smokes normal cannabis, and from someone who doesn’t smoke cannabis at all.”
Regardless of whether there is a direct cause-and-effect, Dazzan urged pot users and public health workers to think about marijuana as they would think of alcohol: different varieties (like beer vs. whiskey) could have widely different effects on the body.
In February, scientists at the UK Institute of Psychiatry reported that wider availability of “skunk” marijuana in south London could be behind a rise in the proportion of new cases of psychosis linked to marijuana use.