Cannabis Use at Age 20 Predicted Worse Mental Health and Functioning at Age 24

In a community sample of 863 young adults, cannabis use at age 20 (measured by both self-report and hair THC) predicted increases in psychotic-like experiences, internalizing symptoms, aggression, problematic substance use, and decreased general well-being from ages 20 to 24. Cannabis users also had higher odds of not being in employment, education, or training. Effects were consistent across six different operationalizations of cannabis exposure.

Longitudinal community study with N=863 young adults assessed at ages 20 and 24. Cannabis exposure measured by self-reported frequency and hair THC/CBN concentrations via LC-MS/MS. Multiple linear and logistic regression models adjusted for sex, sociodemographics, and baseline outcomes at age 20.

Using objective hair analysis alongside self-report strengthens confidence that the associations are real rather than artifacts of self-report bias. The consistency across measurement methods is particularly compelling.

This study demonstrates that the negative outcomes associated with cannabis use in young adulthood are not merely reporting artifacts. Whether these effects represent causation or shared vulnerability factors remains the key unanswered question.

Observational design cannot establish causation. Small effect sizes. Cannot rule out reverse causation (pre-existing mental health driving cannabis use). Hair analysis detects cannabis over months, not acute use patterns. Community sample may not capture highest-risk users.