Newswise — Young adults’ use of cannabis and alcohol tends to rise and fall together, rather than one substance substituting for the other, according to a new study. Understanding the relationship between cannabis use and alcohol use is critical for informing policy and public health strategies. Legalizing recreational cannabis use has raised the possibility that cannabis may substitute for risky drinking or other substance use, potentially with less severe public health consequences. Alternatively, legalizing cannabis might lead to higher consumption of both cannabis and alcohol, with escalating problematic effects. Cannabis use has increased among young adults over the past 15 years, though research has not shown that legalizing recreational cannabis has led to greater substance use. The evidence regarding substitution of cannabis for alcohol has been inconclusive, partly because previous studies have not accounted for shifts in individuals’ substance use over time. The study in Alcoholism: Clinical & Experimental Research may be the first that tracks people’s behavioral changes over time, and how their cannabis and alcohol use interact, in a state where cannabis is legal for non-medical use.

Researchers worked with community sample data from 774 young adults (aged 18–23) who reported drinking alcohol in the year before enrollment and lived in Washington state, where cannabis is legal for people aged 21 and older. Fifty-six percent of the participants were female at birth, and 55% were non-Hispanic/Latinx White. In initial surveys, 34% met the criteria for hazardous alcohol use and 26% for hazardous cannabis use. The participants filled out monthly online surveys for 24 consecutive months, reporting the frequency of their use of alcohol and of cannabis. Investigators used statistical analysis to explore associations between the participants’ rates of cannabis and alcohol use, tracking short- and long-term behavioral shifts.

In a given month, about 78% of participants used alcohol and 32% used cannabis. Those whose average use of cannabis was more frequent also tended to use alcohol more frequently on average. Across the two-year span, rates of change in substance use were correlated; increasing cannabis use over time was slightly associated with increasing alcohol use over time. Months of higher frequency of cannabis use — above individuals’ norm — were also characterized by more frequent drinking, suggesting that young adults may engage in higher-risk use of both substances during certain time periods.

The findings suggest that cannabis and alcohol use are complementary, rising and falling together. This alignment is particularly concerning during young adulthood, a period of continued brain development and major life transitions. Prevention and treatment strategies need to address both cannabis and alcohol use, since short-term increases in one are likely to be accompanied by increases in the other. The researchers recommend exploration of young adults’ simultaneous use, which is associated with greater negative outcomes, and the role of motivations, such as social goals versus coping with stress, in the association between alcohol and cannabis use.

Dual trajectories of cannabis and alcohol use among young adults in a state with legal non-medical cannabis. K. Guttmannova, C. Fleming, I. Rhew, D. Abdallah, M. Patrick, J. Duckworth, C. Lee (p xxx).

ACER-20-4715.R1

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