Long-term effects of ketamine: evidence for a persisting impairment of source memory in recreational users

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.

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.

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.

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.

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.