Cannabis and Tobacco Use Linked to Disrupted Mood Regulation

People who use both cannabis and tobacco show measurable differences in brain activity compared to those who rely solely on cannabis, according to new findings from a McGill University team at the Douglas Research Centre.

These results may help clarify why individuals who combine the two substances often experience symptoms such as anxiety and depression, and why attempts to quit cannabis can be more challenging for them than for those who avoid tobacco.

Lead author Rachel Rabin, an Associate Professor in McGill's Department of Psychiatry, emphasized, 'This is the first evidence in humans of a molecular mechanism that may underlie why people who use both cannabis and tobacco experience worse outcomes.' Identifying this mechanism is a crucial step toward finding targets for future medications to treat cannabis use disorder, especially among those who also use tobacco.

Currently, the only available treatments are behavioral therapies like counseling. In Canada, roughly one in twenty individuals who used cannabis in the past year are considered at risk for cannabis use disorder, and for those who consume cannabis more frequently, the rate skyrockets to about one in three.

Researchers noted that while tobacco use is declining overall, a significant majority of cannabis users still report tobacco use. Rabin pointed out that most previous studies have focused on each substance separately, leaving a significant research gap that this early-stage study is beginning to address.

PET scans revealed that individuals who used both cannabis and tobacco had elevated levels of FAAH, an enzyme that breaks down anandamide, often referred to as the 'bliss molecule' due to its influence on mood and stress responses.

Higher FAAH levels correspond to lower anandamide levels, a pattern previously linked to anxiety, depression, and higher relapse rates among those attempting to quit cannabis. The study involved 13 young adults, with eight using only cannabis and five using both cannabis and cigarettes daily.

Cannabis use averaged slightly above one gram per day, while cigarette intake varied from one to twelve per day. Since the data was originally collected for an unrelated project, there was no tobacco-only group for comparison, leading to the possibility that the changes could be caused by tobacco alone.

However, the researchers believe the results indicate a more complex interaction. Co-author Romina Mizrahi, a Professor of Psychiatry and director of the McGill Research Center for Cannabis, remarked on the strong effect observed, highlighting the significant differences between those who used only cannabis and those who combined both substances.

The research team is now recruiting participants who smoke cigarettes and vape nicotine for a follow-up project aimed at exploring whether similar brain changes occur in the absence of cannabis. The study, titled 'A preliminary investigation of tobacco co-use on endocannabinoid activity in people with cannabis use,' was published in Drug and Alcohol Dependence Reports and funded by the National Institute of Mental Health.