Ketamine has been used to probe the biology of psychosis and cognitive dysfunction in humans. High levels of ketamine abuse are associated with persisting psychosis (KPP) in a minority of users. However, relatively little is known about cognitive function among KPP patients and whether the cognitive impairments associated with KPP resemble those of schizophrenia (SZ).
We recruited 149 treatment-seeking patients, including nonpsychotic ketamine users (KNP, n=51), KPP (n=23), and SZ (n=75) patients. The Positive and Negative Syndrome Scale (PANSS) was used to evaluate psychopathology and the Cogstate Brief Battery to assess cognitive function including psychomotor processing speed, attention, working memory, verbal and visual learning and memory, spatial problem solving, and social-emotional cognition.
Ketamine-dependent patients had an extensive history of ketamine use (average duration=7.1±4.2years, average consumption=3.8±2.7g per day). Although KPP patients used relatively less average ketamine daily dose than KNP patients, KPP patients exhibited significantly greater total PANSS score and subscale scores, while these scores in KPP and SZ patients did not differ significantly. After adjusting for demographic characteristics and antipsychotic dose, KPP and SZ patients showed impairments in spatial problem solving and verbal memory compared to KNP patients, but KPP and SZ patients did not significantly differ from each other.
These data suggest that the symptom profile and cognitive impairments associated with persisting psychosis due to chronic heavy ketamine abuse resemble those of schizophrenia, while KNP patients showed significantly less severe symptom profile and cognitive impairment than KPP and SZ.