Dr. Monica Luciana, a psychology professor and research collaborator, said the idea that adolescent cannabis use exacerbates mental health issues and cognitive impairment is a common notion.
“We concluded that there’s very little evidence that cannabis has dramatic effects on cognitive ability, at least from adolescence into adulthood,” Schaefer said.
While the twins using more cannabis are meeting the criteria for more mental health problems, are doing worse in terms of socioeconomic status and scoring slightly lower on vocabulary tests, this is not directly linked to cannabis use, Malone said.
Instead, the researchers’ findings suggest that adolescent cannabis use may cause academic or motivational difficulties that may affect a person’s educational and occupational status later in their life, he said.
Seventy-six percent of the heavier cannabis-using twins continued education beyond high school, compared to 82% of the lighter-use or sober twins. The grade point average differs by an average of approximately 0.2 points between the two siblings.
When the study began, researchers focused on identifying factors that led to cannabis use. As the twins got older, the researchers pivoted to observing the long-term effects of cannabis use. The immediate focus of the study changes to reflect concerns or issues that are relevant to the stage of life the participants are in, Malone said.