Dissertation Defence: Cannabis-Alcohol Co-Use Protects from Drinking Regret Without Increasing Harms

Joey Rootman, supervised by Dr. Zach Walsh, will defend their dissertation titled “Cannabis-Alcohol Co-Use Protects from Drinking Regret Without Increasing Harms” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Psychology – Clinical Psychology.

An abstract for Joey Rootman’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in person defences.

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ABSTRACT

Heavy episodic drinking, defined as three drinks consumed on a single occasion in females and four drinks in males, is a prevalent and dangerous behaviour. It is becoming increasingly common for cannabis to be co-used with alcohol such that the psychoactive effects of the two substances overlap. Research has indicated that the association between cannabis-alcohol co-use and short-term harms may be complicated by third variable factors such as harms, but further research is needed to understand these complexities. Additionally, little is known about how co-use relates to other short-term outcomes beyond harms such as injury or embarrassment. The present study sought to explore the mechanisms by which co-use relates to harm through indirect pathways of harms and psychoactive effects. Furthermore, co-use was investigated in relation to next-day regret and achievement of intended outcomes of cannabis and alcohol use. Ecological momentary assessment methodology was used to collect observations longitudinally among young adults in Canada. At the end of a drinking event, participants completed a validated measure to assess alcohol related stimulation and sedation psychoactive effects. The following morning, participants reported on harms, co-use with cannabis, harms, regret, and intention fulfilment. Co-use was found to be moderated by harms such that co-use was increasingly protective of harms as additional drinks were consumed. Moreover, co-use was associated with significantly less regret relative to when alcohol was consumed without cannabis. Finally, among participants that reported motivation to engage in cannabis- or alcohol-use for the purposes of enhancement, coping, and socializing, co-use was found to better achieve these outcomes compared to alcohol-use alone. Together, these findings indicate that co-use is no more harmful than alcohol-use alone, and at extreme levels of drinking is associated with protective outcomes. Contemporary harm reduction guidelines are designed to discourage cannabis-alcohol co-use with the intention of reducing harm. Findings suggest that empirically informed approaches should focus reduction strategies on harms, rather than co-use. Future research should aim to investigate potential protective effects of co-use to determine contexts where co-use may be harm-reducing.