What is the influence of cannabis use on alcohol use and smoking

Roche DJO, Bujarski S, Green R, Hartwell EE, Leventhal AM, Ray LA. Alcohol, tobacco, and marijuana consumption is associated with increased odds of same-day substance co- and tri-use. Drug and Alcohol Dependence 2019;200:40-49 (open access article)

Why was this study conducted?

Alcohol, tobacco, and cannabis use are correlated behaviors, but few studies have investigated the patterns of daily use among these substances.  To study patterns of same-day alcohol, cigarette, and marijuana use, an ethnicity-diverse sample of 551 participants (mean age 29.0 years with a standard deviation [sd] of 8.2 years) were drawn from baseline data collected for four human laboratory studies about drinking at the University of California, Los Angles. Less than a third (27.5%) of the participants were female.

What does this study add?

The study found the use of alcohol, cannabis or cigarettes independently increased the probably of subsequent, simultaneous co-use of one or even both of the remaining substances. The effect of alcohol or cigarettes predicting cannabis co-use was stronger in men than women, while the additive relationship between drug co-use leading to tri-use appeared stronger in women.

Is there anything else I should know?

The study suggests a pattern of additive co-reinforcement and cue-cross-reactivity, as well as the development of cross-tolerance due to overlapping neurobiological effects, that could help to explain the escalation of co-morbid substance abuse disorders. However, this is an exploratory study conducted with a sample chosen to represent regular-to-heavy drinkers who also had a substantive mean level of cannabis use disorder (mean 7.8, sd=5.98). More research is needed to determine if the results can be generalized to other populations.