Cannabis use in bipolar disorder was mostly not associated with worse cognition

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.

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.

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 "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.

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.