Young people who stop using cannabis or amphetamines before becoming adults experience life success at the same levels of those who have never used drugs, according to a University of Queensland study.
Emeritus Professor Jake Najman said the research was the first to consider persistent use, rather than the age of first consumption, when predicting adult life success in adolescent drug users.
We found no significant impact on adult life in study participants who started using cannabis, or cannabis and amphetamine before turning 21, but who stopped before they reached the age of 30.
However, we found people who used cannabis and amphetamines at 30 had substantially lower levels of life success."
The study found the age of drug use onset ranged between 15 and 19 years old, with around one in five, or 22 per cent of participants experiencing a cannabis use disorder and 4 percent an amphetamine use disorder.
The majority of those using the drugs before 21 years of age were using a few times a month or less often."
Emeritus Professor Jake Najman, University of Queensland
Researchers used nine factors to determine life success, including education, family income, home ownership, social stability, quality and quantity of intimate relationships, current relationship status and life satisfaction and happiness.
Emeritus Professor Najman said the few long-term studies that had previously examined this issue focused on specific health or social outcomes, such as mental health, crime, or HIV risk.
"As a result, many questions have remained unanswered about the overall life impact of particular patterns of drug use and their specific outcomes," he said.
"The life course trajectory of drug users suggests an important link between continued drug use from adolescence into young adulthood, and great impairment across several life success factors over time.
"Antisocial behavior and contact with the criminal justice system are the strongest predictors of continued drug use, along with problems at school and aggressive or delinquent behavior early in life.
"These findings raise the possibility that targeted interventions for children who show early signs of antisocial behavior or poor school performance may reduce drug use and lead to improved life success."
This study used longitudinal data from the Mater-University of Queensland Study of Pregnancy (MUSP), which involved 8448 mothers and 2900 children self-reporting cannabis and amphetamines use up to the age of 21 year, and again aged 30.
Najman, J.M., et al. (2022) Do cannabis and amphetamine use in adolescence predict adult life success: a longitudinal study. Addiction Research & Theory. doi.org/10.1080/16066359.2022.2032679.