Quitting cannabis use in your 20s significantly reduces your chance of progressing to other illicit drug use, according to research published online in the Journal of Epidemiology and Community Health.
The research from the National Drug and Alcohol Research Centre at the University of New South Wales found that while cannabis use among Australians declines throughout their 20s, those who are using are more likely to be using weekly or more. These regular users have an increased risk of using other drugs compared with occasional users.
While never having used cannabis was the most protective of uptake of any substance, licit or illicit, cannabis users who quit in their 20s were a third to half as likely to take up illicit drugs — cocaine, ecstasy and amphetamine — as occasional users.
Those who used weekly were two to three times more likely to start using illicit drugs than occasional users.
Daily users were six times as likely to start smoking cigarettes. Daily users were also less likely to give up all other drugs except cocaine.
The findings are based on secondary analyses of a landmark study of nearly 2000 Victorian secondary school students who have been followed up and interviewed over 13 years, starting in 1992. The students were interviewed at six six-monthly intervals during their teens and then again when they were aged 20-21, 24-25, and 29.
Lead author of the study, Dr Wendy Swift from the National Drug and Alcohol Research Centre at the University of New South Wales, said that while most studies on the relationship between cannabis and other drug use have focussed on adolescents this study is one of the first to look at what happens to cannabis users as young adults aged up to 29 years.
Overall, while there was an overall decrease in cannabis use in young adulthood, the proportion of cannabis users who smoked the drug weekly to daily almost doubled.
“What we found is that cannabis use dropped off markedly as people progressed through their twenties — 58 per cent of the cohort reported using cannabis at age 20 compared with only 28 per cent using at age 29 — but a significant proportion of these remaining users were using more frequently and were more likely to start or continue using illicit drugs,” said Dr Swift.
Those who had never used cannabis were the least likely to begin using any other drugs, and were most likely to give up cigarette smoking and high-risk drinking in their 20s. At any point in time use of amphetamine, cocaine or ecstasy was virtually non-existent among non-users of cannabis.
“This study provides compelling evidence of the continuing association between cannabis, licit and other illicit drug use well into young adulthood,” conclude the authors. “Findings from this study suggest discouraging users from increasing their use and assisting them to quit altogether have great potential to reduce harms associated with both licit and illicit drugs in young adults.”
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