Does cannabis use impact cognitive behavioural therapy outcomes for anxiety and related disorders? A preliminary examination.

Objectives: The current study examined whether cannabis use frequency and cannabis-related problem severity (as per the Cannabis Use Disorder Identification Test-Revised) predicted outcomes of cognitive behavioural therapy (CBT) for anxiety and related disorders. It was predicted that greater frequency of cannabis use and greater cannabis-related problem severity would be associated with dampened treatment outcomes compared to less severe cannabis use presentations.

Methods: Participants were 253 adults seeking treatment for anxiety and related disorders. Cannabis use was categorized as non-use (n = 135), infrequent use (using monthly to 4 times per month; n = 45), and frequent use (using 2 or more times per week; n = 73). Individuals who reported using cannabis completed cannabis use and cannabis-related problem measures before starting a CBT group. Participants also completed a weekly symptom-specific measure of anxiety symptoms throughout CBT.

Results: As hypothesized, frequent cannabis use was associated with poorer outcomes in CBT for anxiety and related disorders compared to non-use. Despite this, individuals who used cannabis frequently still experienced a statistically significant decrease in their anxiety symptoms from pre-to post-CBT, with a large effect size (d = -0.87). Cannabis-related problems was not a significant predictor of CBT outcomes.

Conclusions: Cannabis use frequency was associated with poorer CBT outcomes for anxiety and related disorders, however these individuals still made notable treatment gains. The mechanism driving this relationship remains unclear. Future studies should attempt to replicate the current findings and examine possible mechanisms.