Background: While some studies have reported that early age of onset of cannabis and amphetamine use predicts a range of adverse outcomes, these findings are rarely adjusted for other predictors of adverse outcomes or subsequent drug use over the adult life course. These studies have not addressed the possibility that it is subsequent rather than early age of onset of drug use that may predict adult life success.

Methods: Data are from the Mater-University of Queensland Study of Pregnancy (MUSP). At 21 years, respondents self-reported their use of cannabis and amphetamines and completed the Composite International Diagnostic Interview (CIDI) on lifetime ever use of cannabis and amphetamines. At 30 years, respondents self-reported their past-year use of cannabis and amphetamines. The outcome measure is a composite measure of life success at the 30-years follow-up. Associations are adjusted for covariates at the 14-year follow-up.

Results: Adolescent behavior problems predict drug use at 21 years, drug use and life success at 30 years. The association between early age of onset cannabis use, amphetamine use and cannabis and amphetamine use and adult life success is not statistically significant once adjusted for cannabis and amphetamine use at the 30-year follow-up. Concurrent cannabis use at the 30-year follow-up is strongly related to life success.

Conclusions: In a community sample, cannabis as well as cannabis and amphetamine use and/or use disorder in the adolescent period does not appear to predict life success in adulthood for those whose use has ceased prior to 30 years of age.