Prospective memory deficits associated with the recreational use of ketamine

Objective Research into the cognitive consequences of the recreational use of ketamine in humans is sparse. Research that does exist has indicated impairments in cognition and memory, including deficits in working memory and executive function. Whether such deficits extend to everyday memory, such as prospective memory (PM: memory for future plans and actions), is unclear. The present study attempts to address this by comparing recreational ketamine users with a group of non-users on self-reported and objective measures of PM. Method An existing-groups design was utilised, comparing a group of 18 recreational ketamine users (using ketamine between 1-3 times per week, but had not used the substance for at least 48 hours) and 19 non-users (who reported never having used ketamine). Scores on the self-report Prospective and Retrospective Memory Questionnaire (PRMQ) and scores on a Prospective Remembering Video Procedure (PRVP: an objective measure of PM for location-action combinations remembered whilst viewing a video clip of busy shopping district) constituted the dependent measures. Age, mood, IQ, and other drug use were also measured. Results A series of one-way ANOVAs revealed no between-group differences in terms of age, mood, IQ and other drug use. A MANCOVA (controlling for retrospective memory scores) revealed that although the two groups did not differ in terms of their self-reported PM deficits on the PRMQ, ketamine users did recall significantly fewer location-action combinations on the PRVP than the non-using group. Conclusion The results from the present study suggest that recreational ketamine users exhibit deficits in their objective PM that are independent of retrospective memory. PM deficits should therefore be added to the growing list of neuropsychological sequelae associated with sub-acute recreational usage of ketamine.