Researchers say adolescent use of weed and amphetamines does not adversely affect future life success

Those who ditch their habits before the age of 30 “do not have lower economic and relationship success, and life quality.”

A new study out of Australia suggests that the future life success of adolescent cannabis and amphetamine consumers is not affected if they break the habit before the age of 30.

“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,” authors explain in the study, published this week in the peer-reviewed journal, Addiction Research & Theory.

A University of Queensland study from 2015 found lower quality of life (QoL) in the early teenage years predicted subsequent onset of cannabis use in young adulthood.

“Frequent use of cannabis does not appear to enhance the user’s QOL and appears to be associated with a reduced QOL into young adulthood.”

With the latest study, investigators wanted to shed light on the extent that cannabis and amphetamines use up to age 21 predicts life success at age 30. Onset use among study participants ranged from 15 to 19 years.

Researchers used data on 2,350 Australian children born to mothers included in the Mater-University of Queensland Study of Pregnancy. The children were tested at age 14 for IQ, mental health and aggression/delinquency, they were interviewed at age 21 and also self-reported their use of cannabis and amphetamines, and they completed the same self-report at age 30.

A composite measure of life success — which took into account socioeconomic, quality of life and quality of intimate relationships — was taken at age 30.

In all, the findings indicate 22 per cent of participants had ever had a cannabis use disorder and four per cent had problematic amphetamines use.

By age 21, problematic cannabis use was slightly lower at 19 per cent, but just 0.7 per cent of participants reported problematic amphetamine use and three per cent noted problematic use of both drugs.

Of those reporting problematic drug use, issues persisted at age 30 for 36 per cent of those taking cannabis and 60 per cent of those on both substances.

“Adolescent behaviour problems predict drug use at 21 years, and drug use and life success at 30 years,” authors note in the study.

That said, investigators found an association between early-age onset use of cannabis, amphetamines or both 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 followup is strongly related to life success.”

Researchers point out that past studies related to the early age of onset of the two substances have suggested a range of adverse outcomes or drug use during adulthood. “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,” the study notes.

A study published in 2021 suggests that cannabis use during adolescence is associated with altered neurodevelopment. A review article released in 2020 further notes that “current evidence indicates that adolescence is a sensitive period during which cannabis use may result in adverse neurocognitive effects that appear to show a level of permanency into adulthood.”

In another study from 2021, authors write their findings “suggest that cannabis use in adolescence has potentially causal, deleterious effects on adolescent academic functioning and young-adult socioeconomic outcomes despite little evidence suggesting a strong, causal influence on adult mental health or cognitive ability.”

Citing the importance of stopping drug use in early adulthood to avoid compromising adult health and well-being, the press release notes researchers are calling on policy-makers to address teen behaviour issues. Treatment should target individuals whose drug use persists beyond early adulthood, they say.

“What seems to best predict low life success outcomes is the persistence (over a longer course of time) of cannabis and amphetamine use,” lead author Professor Jake Najman of the University of Queensland says in the statement.

“Our findings linking problem behaviour and school problems in adolescence with drug use and life success represent an opportunity for policy-makers to alter the young person’s life trajectory,” Najman contends.

Given the high rates of drug use by adolescents, the press release cites authors as saying “more research is needed into interventions to prevent the persistence of drug use into adulthood, which is strongly linked to lower life success.”