A new study shows that the lasting effects of adolescent cannabis use can be observed on important cognitive functions and appear to be more pronounced than those observed for alcohol.

Beyond acute intoxicating effects, alcohol and cannabis misuse has been associated with impairments in learning, memory, attention and decision-making, as well as with lower academic performance.

“While many studies have reported group differences in cognitive performance between young users and non-users, what had yet to be established was the causal and lasting effects of teen substance use on cognitive development,” said Jean-François G. Morin, co-author and a Ph.D. student at the Université de Montréal.

According to senior author Dr. Patricia Conrod, from the Department of Psychiatry at Université de Montréal, the study was “unique in that it followed a large sample of high school students from 7th to 10th grade using cognitive and substance-use measures. Using this big-data approach, we were able to model the complex nature of the relationship between these sets of variables.”

The research team followed 3,826 Canadian adolescents over a period of four years. From this sample, they hoped to understand the relationship between alcohol use, cannabis use and cognitive development among adolescents at all levels of consumption: abstinent, occasional consumer or high consumer.

Using what they called a “developmentally sensitive design,” the researchers investigated relationships between year-to-year changes in substance use and cognitive development across a number of cognitive domains, such as recall memory, perceptual reasoning, inhibition and working memory.

Multi-level regression models were used to simultaneously test vulnerability and concurrent and lasting effects on each cognitive domain, the researchers explained.

The study found that cannabis and alcohol use in adolescence was associated with generally lower performance on all cognitive domains.

“However, further increases in cannabis use, but not alcohol consumption, showed additional concurrent and lagged effects on cognitive functions, such as perceptual reasoning, memory recall, working memory, and inhibitory control,” Conrod said.

“Of particular concern was the finding that cannabis use was associated with lasting effects on a measure of inhibitory control, which is a risk factor for other addictive behaviors, and might explain why early onset cannabis use is a risk factor for other addictions.”

“Some of these effects are even more pronounced when consumption begins earlier in adolescence,” Morin added.

The study’s findings highlight the importance of protecting youth from the adverse effects of cannabis and alcohol consumption through greater investment in drug-prevention programs, the researchers noted.

“It will be important to conduct similar analyses with this cohort or similar cohorts as they transition to young adulthood, when alcohol and cannabis use become more severe,” Conrod said.

“This might be particularly relevant for alcohol effects. While this study did not detect effects of teen alcohol consumption on cognitive development, the neurotoxic effects may be observable in specific subgroups differentiated based on the level of consumption, gender or age.”

“We also want to identify if these effects on brain development are related to other difficulties, such as poor academic performance, neuroanatomical damage, and the risk of future addiction or mental health disorders,” Morin concluded.

The study was published in the American Journal of Psychiatry.

Source: University of Montreal