A scoping review found only 6 studies on cannabis and cognition in bipolar disorder, with most suggesting no significant cognitive impairment from cannabis use, and two finding better performance in some domains.
Clinicians treating bipolar disorder and researchers studying cannabis-cognition interactions.
Only 6 studies exist on cannabis and cognition in bipolar disorder
What the researchers found
Of 6 qualifying studies, two found cannabis use in bipolar disorder was associated with better performance in some cognitive domains, three found no association, and one found worse overall cognition. No animal studies met inclusion criteria. The limited evidence base prevents strong conclusions.
Why it matters
Cannabis use is highly comorbid with bipolar disorder, and cognitive impairment is a core feature of the condition. The surprising finding that cannabis may not worsen (and might even improve) cognition in bipolar disorder parallels similar findings in schizophrenia and deserves further investigation.
The numbers in context
6 studies met inclusion criteria. 2 found better cognition with cannabis use. 3 found no association. 1 found worse cognition. Zero animal studies found.
How the study worked
Systematic scoping review searching PubMed, Embase, CINAHL, Web of Science, and PsycINFO for studies on cannabis use and cognition in bipolar disorder or relevant animal models. Six human observational studies met inclusion criteria.
What this study cannot tell us
Only 6 studies, all observational. Cannot determine causation. Wide variation in how cannabis use was measured across studies. No studies controlled for cannabis use frequency, quantity, or type.
How to read the evidence
Only 6 qualifying studies, all observational. The field is far too sparse for definitive conclusions.
When this study was published
2021 systematic scoping review.
The bigger picture
The "better cognition in cannabis-using patients" finding likely reflects selection effects: people who develop bipolar disorder while using cannabis may have needed less underlying vulnerability (and started from higher cognitive baselines) compared to those who developed bipolar disorder without cannabis exposure.
Questions still open
- Would controlled studies show different results? Are the better-performing cannabis users a distinct subtype of bipolar disorder? Does the timing of cannabis use relative to bipolar onset matter for cognitive outcomes?
Common questions
Does cannabis impair thinking in people with bipolar disorder?
Why might cannabis users with bipolar disorder perform better cognitively?
Read the original research
The relationship between cannabis use and cognition in people with bipolar disorder: A systematic scoping review.
Psychiatry research, 297, 113695
Citation
Jordan Walter, T; Pocuca, Nina; Young, Jared W; Geyer, Mark A; Minassian, Arpi; Perry, William. (2021). The relationship between cannabis use and cognition in people with bipolar disorder: A systematic scoping review.. Psychiatry research, 297, 113695. https://doi.org/10.1016/j.psychres.2020.113695
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