According to a new study carried out by researchers from McMaster University and published in the journal JAMA Pediatrics, teens who use cannabis have significantly worse outcomes at school. The research study involved a meta-analysis of 63 scientific studies with 438 329 participants, with a median range of 16 years old. Specifically, it was found that adolescents and young adults who used cannabis had lower grades (less likely to get As and Bs) and worse school attendance. In addition, they had higher odds of dropping out of school and were less likely to complete high school or college compared with their peers who did not use cannabis.

Moreover, the study’s results revealed that cannabis use also negatively impacted postsecondary education, with young adults who used cannabis being significantly less likely to enroll in a university or to receive a postsecondary degree.

“Adolescence and young adulthood are critical periods for brain development and increasing acceptance and legalization of cannabis have raised concerns about implications for academic performance,” stated the researchers in the article. “Chronic use among adolescents has been linked to long-term changes in brain architecture, resulting in impaired information processing and decreased cognitive, memory and attentive capacity in adulthood.”

The results also showed that there was also “low-certainty” evidence that cannabis use in youth was linked to unemployment. What’s more, all the risks identified in the study increased with the frequency of cannabis use, as well as early use (at or before the age of 16 years).

While the authors noted that the data cannot conclusively prove that cannabis causes the aforementioned negative outcomes, as part of their analysis, they adjusted the results for other substance use and mental disorders. They also noted that adolescents and young adults with mental health issues or other substance-use disorders may have a predisposition to both use cannabis and have a lower performance at school.