Mapping the acute effects of cannabis on multiple memory domains: A randomized, double-blind, placebo-controlled study

Background: One of the most robust acute effects of cannabis is impaired memory. Although memory is not a unitary construct, most cannabis research has focused on verbal memory. Less is known about its effects on more ecologically valid domains of memory, such as prospective and temporal order memory. Methods: We conducted a randomized, double-blind, placebo-controlled study to map out which aspects of memory are impaired following acute cannabis use. Cannabis-using participants ( N = 120) were randomly assigned to vaporize flower containing 0 mg Δ-9-tetrahydrocannbinol (THC; placebo), 20 mg THC (moderate dose) or 40 mg THC (high dose) before completing a battery of memory tests, including tests of verbal memory (immediate, delayed, short-term, working), visuospatial memory (immediate, delayed, short-term, working), prospective memory (event-cued, time-cued), source memory, false memory, episodic content memory, and temporal order memory. Results: Relative to placebo, cannabis increased susceptibility to false memories and detrimentally impacted verbal memory (immediate, delayed, working), visuospatial memory (immediate, delayed), event-cued prospective memory, source memory, and temporal order memory. There were no significant differences between the moderate and high dose groups. Conclusion: This is the first study to detect acute effects of cannabis on prospective memory and temporal order memory, which is important because these tests better reflect everyday memory and predict daily functioning. Collectively, these results indicate that acute cannabis use has broad detrimental effects on most domains of memory rather than selectively impairing a limited number of these domains. The study was pre-registered on clinicaltrials.gov (#NCT05488509) at https://clinicaltrials.gov/study/NCT05488509 .