Whether adolescent cannabis use causes adverse social outcomes or whether it is merely a marker of other causes is not clear from existing research. Investigators in New Zealand studied a birth cohort of 1003 subjects born in 1977 to determine the association between cannabis use from ages 14 to 21 and education, income, employment, relationship quality, and life satisfaction at age 25. Potential confounding factors, including socioeconomic status, family functioning, exposure to child abuse, childhood and adolescent adjustment, early adolescent academic achievement, and comorbid mental health and substance use disorders, were prospectively measured and adjusted for in the final analyses. Subjects were divided into 6 groups based on self-reported cannabis use ranging from no use to use on greater than 400 occasions.

• Subjects demonstrated statistically significant linear trends for decreased university degree attainment, decreased income, increased welfare dependence, increased unemployment, decreased relationship satisfaction, and decreased life satisfaction with increased cannabis use in adolescence.
• Even after adjusting for covariable factors, these same linear trends were found regardless of whether cannabis categories were based on total times used, average annual frequency, or age periods (14–21 years or 14–18 years).

Comments by Michael Levy, PhD
This study demonstrates that heavy cannabis use during adolescence is associated with numerous adverse consequences in young adulthood. Although the precise reasons for this are not clear, this relationship suggests that heavy cannabis use during adolescence should be prevented and addressed in treatment whenever possible.