New research released this month in the American Journal of Psychiatry has found that marijuana causes long-lasting damage to an adolescent’s developing brain.

Drug and alcohol use during adolescence has always been a health concern because the human brain continues to develop into young adulthood. Drugs have been proven to cause problems with learning, attention, decision-making, and academic performance. This most recent study, which was conducted by scientists at the University of Montreal, is unique because it examined the effects of both marijuana and alcohol on a teen’s cognitive skill over time. The study found the impact on thinking skills, memory and behavior in teens increased as cannabis use increased, and perhaps more importantly, the effects were lasting, unlike those of alcohol.

The study tracked and tested over 3,800 adolescents from 31 Montreal-area schools over four years. The teens, who started participating in the study when they were 13, agreed to provide annual reports of how frequently they used marijuana and alcohol. To insure honest answers, students were assured that parents and teachers would not have access to the information, unless there was an imminent safety risk. The students took computer-based cognitive tests each year that measured recall memory, perceptual reasoning, inhibition and short-term memory.

The National Institute on Drug Abuse for Teens reports that 5.9% of high school seniors used marijuana daily in 2017. In the Canada study, 28% of the teenagers admitted to some kind of marijuana use. In comparison, 75% of the teens said they drank alcohol as least occasionally. The head researcher expected alcohol to have more of an impact on the teens’ brains, but the research detected greater increases in errors in cognitive tests on the teenagers using marijuana – while they were taking the drug and also after they had stopped. The study concluded that marijuana had a more damaging effect on teenagers’ long-term cognitive abilities than alcohol.

Another recent study published in June of 2018 in JAMA Psychiatry discovered that young people who used marijuana frequently were more likely to have lower scores on tests of memory, learning new information, and higher-level thinking involving problem solving and processing information.