“What we found was a little surprising,” says lead researcher Jordan Bechtold, a psychology research fellow at the University of Pittsburgh Medical Center. “There were no differences in any of the mental or physical health outcomes that we measured regardless of the amount of frequency of marijuana used during adolescence.”
For the study – published in the journal Psychology of Addictive Behaviors – researched examined data taken from the Pittsburgh Youth Study, a longitudinal study that attempted to track the development of antisocial and delinquent behavior among boys attending public school in Pittsburgh from 1987 to 1988.
For 10 years, researchers conducted follow-up interviews with some of these individuals (those in the seventh grade), first semiannually, and then annually until they turned 25. When they turned 35, researchers subjected them to one last interview.
Once the final interview was finished, researchers separated participants into groups; those who rarely or never used cannabis (46%); those who mostly used it in their teens (11%); those who took up the habit in adulthood (21%); and those who started early and become regular, consistent cannabis consumers even into adulthood (22%). They then compared the health status of these groups to each other, controlling for factors such as tobacco use.
“[F]indings from this sample indicated that chronic marijuana users were not more likely than late increasing users, adolescence-limited users, or low/nonusers to experience several physical or mental health problems in their mid-30s,” says Bechtold. “In fact, there were no significant differences between marijuana trajectory groups in terms of adult health outcomes, even when models were run without controlling for potential confounds.”