The relationship between cannabis use and cognition in people with bipolar disorder: A systematic scoping review

•Much remains unknown about the health effects of cannabis use in BD.•This study reviewed the relationship between cannabis use and cognition in BD.•We found six observational human studies on cannabis use and cognition in BD.•Most studies found cannabis is not associated with markedly worse cognition in BD.•Given mixed findings and unanswered questions, additional studies are needed. Bipolar disorder (BD) and cannabis use are highly comorbid and are each associated with cognitive impairment. Given the prevalence of cannabis use in people with BD, it is important to understand whether the two interact to impact cognitive function. We performed a systematic scoping review to determine what is currently known in this field. We systematically searched PubMed, Embase, CINAHL, Web of Science, and PsycINFO for studies on the relationship between cannabis use and cognition in people with BD or relevant animal models. Six observational human studies and no animal studies met inclusion criteria. Two studies found cannabis use in BD was associated with better performance in some cognitive domains, while three studies found no association. One study found cannabis use in BD was associated with worse overall cognition. Overall, most identified studies suggest cannabis use is not associated with significant cognitive impairment in BD; however, the scope of knowledge in this field is limited, and more systematic studies are clearly required. Future studies should focus on longitudinal and experimental trials, and well-controlled observational studies with rigorous quantification of the onset, frequency, quantity, duration, and type of cannabis use, as well as BD illness features.