Interactions Between Tobacco and Cannabis Use on the Human Brain

Marijuana and tobacco remain two of the most abused substances worldwide. In many countries, smoked marijuana is almost exclusively mixed with tobacco, yet the interactive effects of these two substances on the human brain and cognition are poorly understood.

Marijuana use has been associated with lower gray matter volume in brain regions that are particularly dense in cannabinoid type 1 (CB1) receptors, including the hippocampus, amygdala, striatum cerebellum and medial frontal regions (Cousijn et al., 2012). Furthermore, cannabis users exhibit deficits in facets of cognition that are dependent on these brain regions, including working memory, impulsivity and attention (see Crean et al., 2012 for a review). However, it is currently unknown whether cannabis smokers’ use of tobacco (whether mixed with cannabis in a joint, or smoked in a conventional cigarette) influences these findings. This is particularly important, as nicotine use can also result in structural and neurochemical changes in the above brain regions (e.g. Faulkner et al., 2020; Fritz et al., 2014), as well as in deficits in the above-listed cognition faculties (e.g. Faulkner and Machon et al., in prep).

We are therefore examining the effects of cannabis and tobacco use on brain structure, function and chemistry, as well as on cognition, in cannabis-using tobacco smokers, non-cannabis-using tobacco smokers, and controls using MRI, MRS and cognitive tasks. Positive findings may improve public health and influence public policy.