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Marijuana use in adolescence may not affect adult health outcomes

Adolescent use of marijuana, at varying degrees, did not influence mental and physical health outcomes in adulthood, according to study findings in Psychology of Addictive Behaviors.

“Although many large-scale cross-sectional studies have investigated the potential negative health effects of heavy marijuana use, relatively few longitudinal studies have prospectively examined the long-term physical (eg, cancer, respiratory problems) and mental (eg, psychosis, depression) health consequences of early onset chronic use,” study researcher Jordan Bechtold, PhD, of the University of Pittsburgh School of Medicine, and colleagues wrote. “Furthermore, many of the existing studies have produced inconsistent findings, particularly when examining marijuana use as a risk factor for cancer, cardiac illnesses, metabolic diseases, and internalizing disorders.”

Researchers analyzed data from the Pittsburgh Youth Study, a prospective, longitudinal study which enrolled male Pittsburgh public school students in the late 1980s to assess development of delinquency, substance use and mental health problems in this population. Study participants, aged 14 years at baseline, were surveyed every 6 months for 2.5 years then annually for the next 10 years, with the last consecutive assessment at age 26 years. Study participants were re-interviewed at age 36 years in 2009 and 2010. The follow-up survey included 408 participants. Fifty-four percent of the study cohort was black, 42% were white and 4% were other races or ethnicities.

The study cohort had four distinct subgroups of marijuana users: early-onset chronic users (22%), late increasing users (21%), adolescence-limited users (11%) and low/non-users (46%). Late increasing users began using marijuana later in their teen years and continued using the drug. Early-onset chronic users reported significantly higher marijuana use, which increased during their teen years and peaked at least 200 days per year at age 22 years and then slightly declined as they aged.

“What we found was a little surprising,” Bechtold said in a press release. “There were no differences in any of the mental or physical health outcomes that we measured regardless of the amount or frequency of marijuana used during adolescence.”

There were no significant differences between subgroups of marijuana use regarding self-reported asthma, allergies, headaches and high blood pressure. Groups did not differ in the number of participants having a current health condition that limited physical activity, having a serious physical injury in the past year or having prior history of concussion.

High blood pressure was more common among black men than white men.

Lifetime diagnosis of anxiety disorders, mood disorders or psychotic disorders did not differ among marijuana use subgroups. There were no significant differences in mental health outcomes between black and white males.

Race and marijuana use were not significantly associated when assessing study outcomes, according to researchers.

“Overall, data from this sample provide little to no evidence to suggest that patterns of marijuana use from adolescence to young adulthood, for the black and white young men in the present study, were negatively related to the indicators of physical or mental health studied here,” Bechtold and colleagues wrote. “This does not discredit the work of others. It could be the case that cumulative tetrahydrocannabinol exposure, age of initiation of use, or use at one particular age is more predictive of negative health outcomes than the overall pattern of use between adolescence and adulthood.” – by Amanda Oldt

Disclosure: Please see the full study for a list of all other authors’ relevant financial disclosures.