RATIONALE

Ketamine is an N-methyl-d-aspartate (NMDA)-receptor antagonist that is increasingly being used as a recreational drug. Previous research has shown gross generalised verbal memory impairments persisting 3 days after ketamine use in chronic users, however episodic memory has not specifically investigated in this population.

OBJECTIVE

To determine whether ketamine, on the night of drug use (day 0) and 3 days later, is associated with impaired episodic memory as assessed by a source memory task.

METHODS

Twenty ketamine users and 20 poly-drug controls were compared on a source memory task both on day 0 and 3. Participants also completed questionnaires on both days indexing schizophrenic-like and dissociative symptoms.

RESULTS

On day 0, ketamine abusers were impaired on both source memory and item recognition and scored more highly on schizophrenic and dissociative symptom scales compared to poly-drug controls. On day 3 ketamine abusers only displayed source memory impairments and these positively correlated with the level of schizophrenic-like symptoms on day 0. No differences on day 3 in schizophrenic-like or dissociative symptoms were observed.

CONCLUSIONS

Ketamine abusers exhibit a persisting deficit in source memory on day 3 but not in item recognition. These findings suggest that repeated use of ketamine produces chronic impairments to episodic memory.