A systematic review of the effects of cannabis on cognition in people with multiple sclerosis.

Background: Multiple sclerosis (MS) is a chronic demyelinating disease which leads to sensory, motor, autonomic, and cognitive symptoms. Cannabis is a common way for persons with MS (pwMS) to seek symptomatic therapy. Given the capacity for both cannabis and MS to cause cognitive impairment, it is important to determine whether there is any negative impact when the two co-occur. The objective of this systematic review was to evaluate the effects of cannabis and medicinal cannabinoid products on cognition in pwMS in order to provide guidance to clinicians and enable them to make evidence-based recommendations regarding cannabis and cannabinoid products. Methods: A systematic review was carried out searching common keyword combinations for cannabis and MS across five databases, producing 840 unique articles, 18 of which were included in a qualitative synthesis. Results: Aggregate data from existing studies to date highlight potential impairments from chronic whole-plant cannabis use in commonly affected cognitive domains in multiple sclerosis, including attention and working memory, and to a lesser extent, visual memory, verbal memory, and executive function. Results also suggest that in the short-term, medicinal cannabinoid preparations do not significantly impair cognition and may even ameliorate cognitive symptoms in the context of obtrusive MS disease. The findings are limited by disparities in detail of cannabis use data reported across whole-plant cannabis publications. Conclusion: Existing literature on co-occurrence of cannabis use and MS lacks high quality evidence to recommend for or against cannabis and cannabinoid therapies for pwMS based on cognitive effects. Existing data suggest that cognition may be differentially impacted in pwMS depending on the type of product, the duration of use, and the indication. Future studies on whole-plant cannabis require comprehensive cannabis use data reporting including frequency, dosing, duration, and type of cannabis product. Future studies on medicinal cannabinoid products should be long-term to assess the effects of chronicity.