Cognitive Impairment May Predict Persistent Psychosis in Ketamine Users

syringe and a couple vials
syringe and a couple vials
Ketamine-dependent patients who exhibited psychosis demonstrated levels of spatial problem solving and verbal memory impairment similar to those of patients with schizophrenia.

Researchers of a study published in Schizophrenia Research explored the similarities between the persisting psychosis experienced by approximately 3% of heavy ketamine users and the psychotic symptoms of schizophrenia. In particular, the authors examined cognitive impairments as a possible vulnerability for persisting psychosis.

Ketamine, a short-acting anesthetic, has risen in use as a recreational drug over the last 20 years, particularly in East and Southeast Asia.

The investigators recruited 74 inpatients with ketamine dependence and 75 inpatients with schizophrenia across 3 treatment centers in Taiwan. Ketamine users were further distinguished by whether they exhibited psychotic symptoms >24 hours after administration (n=23) or not (n=51). Participants were age 18 to 65 years, had been diagnosed with ketamine dependence according to the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, and had used ketamine actively >1 year prior to admission.

Patients in the ketamine groups were excluded if they had any other substance use disorder, antipsychotic exposure, or a history of any major psychiatric disorder. Ketamine use patterns were comparable between groups, regardless of whether they experienced persisting psychosis.

The participants’ psychopathology was assessed using the Positive and Negative Syndrome Scale. Cognitive function was rated with the Cogstate Brief Battery, which included spatial problem solving, psychomotor processing speed, attention, working memory, verbal and visual learning memory, and social-emotional cognition.

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Ketamine-dependent patients who exhibited psychosis had significantly greater total Positive and Negative Syndrome Scale scores than those who did not exhibit psychosis. In addition, they demonstrated levels of spatial problem solving and verbal memory impairment similar to those of patients with schizophrenia. Although cognitive function in ketamine users with persistent psychosis is still being investigated, the authors drew a parallel to schizophrenia, in which cognitive dysfunction can be a predictor of the severity of a patient’s functional impairment.

The study was limited by a lack of data on participants’ cognitive functioning prior to index. The authors also noted that the group that did not exhibit psychosis might have cognitive impairments relative to the general population, despite their better performance in the context of the study.


Cheng W-J, Chen C-H, Chen C-K, et al. Similar psychotic and cognitive profile between ketamine dependence with persistent psychosis and schizophrenia [published online March 3, 2018]. Schizophrenia Research. doi:10.1016/j.schres.2018.02.049