Long-Term Effects of Marijuana Use in Adolescence and Emerging Adulthood on Adult Functioning: A Developmental Perspective

Introduction: With the trend toward decriminalization and legalization of recreational marijuana use in the U.S., it is important to delineate the long-term consequences of use, especially early-onset use. Nonetheless, few studies have prospectively followed youth from early adolescence into adulthood to determine the effects of marijuana on adult functioning. This paper examines differences in adult functioning (at age 35) for four groups based on frequency of marijuana use annually between ages 13 and 25: 1) non/light (NU; 46%), 2) adolescence-limited (AL; 11%), 3) late-onset (LO; 21%), and 4) chronic heavy (CH; 22%) users. Methods: Data come from the oldest cohort from the Pittsburgh Youth Study, a prospective study of young men interviewed at least annually from the 7^th grade until age 25 and then again at age 35 (N=497). At age 35, men reported on their functioning across seven domains: intimate partner status, relationship quality, partner deviance, peer deviance, social support, parenting, education/occupational success, and perceptions of life. All analyses were conducted in Mplus. Latent class growth analysis was used to identify trajectory groups and the auxiliary function 3-step procedure was used to predict adult functioning from group membership. Results: Significant group differences were found across all domains except social support. Post hoc comparisons indicated that, compared to NU, CH were less likely to be married, pay child support, be employed, have a high school degree, and be satisfied with their lives, more likely to have children outside of the house and from multiple partners and have substance-using partners and peers and deviant peers, and reported lower educational attainment, occupational status, and dyadic agreement. LO, compared to NU, were less satisfied with their lives, and were more likely to have substance-using and deviant peers, binge drinking partners, children from multiple women, and be unemployed. AL, compared to NU, were less likely to have graduated from high school, more likely to have substance-using and deviant peers, and less satisfied with their lives. There were very few significant differences among CH, AL, and LO. Conclusions: Chronic heavy marijuana use beginning in early adolescence interferes with adult role attainment and functioning, especially in the areas of educational/occupational success and parenting. Those who use early but mature out are still at risk for lack of educational success, life dissatisfaction, and involvement with deviant peers. Thus, interventions with early onset marijuana users are needed, especially to prevent school dropout. Late-onset users also reported several problems in adulthood, suggesting that delay of onset may prevent some but not all later problems.