Marijuana expectancies and relationships with adolescent and adult marijuana use.

Background: Outcome expectancy is a central construct in models of addiction and relapse. Much expectancy research has been conducted in the context of alcohol; however, less is known about the structure of expectancies for marijuana and their associations with marijuana use outcomes.

Methods: The data are taken from waves 3 and 4 of a longitudinal high-risk study of parents and adolescent offspring. Of those families who were retained at wave 3, 225 were high-risk and 205 were matched controls (low-risk). In the present study, we examine the factorial structure of marijuana expectancies (wave 3) in the offspring (using an instrument adapted from the alcohol literature) and test whether expectancies mediate the associations of familial risk for substance use, lifetime marijuana use in adolescence (wave 3) and current use in young adulthood (wave 4; reported approximately 5 years later).

Results: We quantified four marijuana expectancy factors similar to those identified in previous studies when the offspring were adolescents (Mn age=15.2) and results of our mediation models suggest that negative marijuana expectancies (but not positive expectancies) together with lifetime adolescent marijuana use completely mediated the association between familial risk and current use of marijuana during young adulthood (Mn age=20.2).

Conclusion: Familial risk for current marijuana use in young adulthood appears to be transmitted through two orthogonal, prospective pathways. One pathway involves marijuana use during adolescence, and the second pathway involves reduced expectancies that using marijuana will result in cognitive and behavioral impairments.