New Study Says Adolescent Cognitive Development is Impacted by Cannabis and Alcohol Use

A study published Wednesday in the American Journal of Psychiatry is shedding new light on the changing relationships between adolescents’ substance use and their cognitive development. And it may even overturn some common assumptions about the relative risks posed to young people by alcohol and cannabis. Legalization advocates often present cannabis as a relatively safer substance than alcohol. It’s a claim that most research on adults supports. But the reality is significantly less clear when it comes to the two substances’ impact on developing brains. Indeed, researchers in Quebec are suggesting the reverse, that cannabis is more deleterious on young minds than alcohol.

Cannabis Impacted Teens’ Cognitive Ability More Than Alcohol, Researchers Say

Headed up by lead author Patricia J. Conrad, researchers with the University of Montreal tracked 3,826 Montreal teens’ alcohol and cannabis use over four years, beginning in the seventh grade, at age 13. The study’s sample size represents students across 31 different schools and 5 percent of all students entering high school in the 2012-2013 academic year in the Greater Montreal area.

Researchers assured student participants that parents and teachers would not have access to their self-reported data on cannabis and alcohol use. And over the four year period, participants performed tasks that measured their cognitive development. The study collected data on recall and working memory, perceptual reasoning and inhibition using computerized assessments.

The study, titled “A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development,” then ran the data through models to determine participants’ vulnerability to cognitive effects, the duration of short-term and long-term effects, and how age influenced their development.

As they expected, researchers detected commonalities between vulnerability effects on cognition for both alcohol and cannabis across all domains, from memory to reasoning. But it was cannabis use, not alcohol consumption, that produced delayed neurotoxic effected on inhibitory control, working and recall memory and perceptual reasoning, researchers say. Furthermore, they found the effects of cannabis on cognition to be independent of the effects of alcohol.

As a result, researchers concluded that “the concurrent and lasting effects of adolescent cannabis use can be observed on important cognitive functions and appear to be more pronounced than those observed for alcohol.” Or in other words, weed was worse on teen brains than alcohol, at least among the study’s population.

Research Continues To Show How Cannabis Can Harm Developing Brains

Speaking with NBC News, the study’s lead researcher and primary author Patricia J. Conrad said “cannabis causes cognitive impairment and delayed cognitive development in adolescents.” Conrad is a professor of psychiatry at the University of Montreal.  She has co-authored multiple studies investigating the psychological and cognitive effects of teen cannabis use. Speaking about her newly published report, Conrad says the study focused on the neuropsychological effects of cannabis and alcohol. The physiological health risks posed by alcohol and cannabis, however, were not part of the study.

Alcohol consumption may pose a more significant risk to teens’ health than cannabis use. But Conrad and her team say that when it comes to young brains’ ability to think, cannabis is more harmful than alcohol. It’s a conclusion corroborated by scientists at the University of Pennsylvania. In June, they published a study in JAMA Psychiatry documenting how cannabis hurts adolescents’ memory, their ability to learn new information and perform higher-level analytical thinking necessary for problem solving. Conrad says studies like these are significant, because they show how young peoples’ cannabis use is directly linked to their cognitive function and abilities later in life.