Newswise — Cannabis use can worsen some consequences of alcohol use among young adult drinkers over time, according to a new study which tracked the frequency of cannabis use and negative drinking outcomes among college students over three years. More than one in five young drinkers use cannabis, often (but not always) at the same time as drinking alcohol. This is a concern because the effects of cannabis might combine with those of alcohol to increase negative outcomes of drinking, such as impaired driving or developing an alcohol use disorder. Although previous research has suggested a link between cannabis use and alcohol consequences, there have been few long-term evaluations of the impact of fluctuations in cannabis use on alcohol consequences over time. The latest study, published in the journal Alcoholism: Clinical and Experimental Research, was conducted by researchers in Toronto, Ontario, and Buffalo, New York.

Data were analyzed from nearly one thousand students, from two US universities, who underwent four assessments per year over their first three years of college. At each assessment, participants reported how often they had used cannabis over the previous month, their weekly alcohol consumption over the same timeframe, and any resulting alcohol-related consequences. For the latter, students indicated whether they had experienced any of 48 problems encompassing eight different types of alcohol-related harm – from relatively less severe consequences such as hangovers and social embarrassment through to more severe consequences such as alcohol dependence.

At the first assessment, almost two-thirds of students reported drinking alcohol in the previous month, and one-fifth reported cannabis use. Among those who used cannabis, one-third had used it only once in the previous month, a further third reported using it two or three times, and the remainder had used cannabis at least weekly, with 5% of cannabis users reporting daily use. Statistical modeling showed that, after accounting for changes in alcohol use, an increase in the frequency of cannabis use among individuals over time was associated with increases in some of the more severe types of alcohol consequences – including risky behaviors (such as impaired driving), poor self-care, and symptoms of alcohol dependence. However, there was no association between fluctuations in cannabis use and changes in the less severe types of alcohol consequences (such as social consequences), or with the total number of consequences experienced.

The findings underscore the importance of considering the longer-term impact of changes in cannabis use on different alcohol outcomes. Cannabis and alcohol may have additive effects on cognitive and behavioral impairment, perhaps accounting for the increase in more severe types of consequence that may emerge at greater levels of impairment. However, the researchers note that further research will be needed to understand the causes of the associations observed. More broadly, it is hoped that the findings will inform harm reduction interventions for young adult drinkers who use cannabis.

Does Cannabis Use Predict More Severe Types of Alcohol Consequences? Longitudinal Associations in a Three-Year Study of College Students. J.D. Wardell, G.A. Egerton, J.P. Read (pages xxx).

ACER-19-4171.R1

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