Evidence suggests that repeated or chronic ketamine use, as compared to acute ketamine users, posed a higher clinical risk of developing psychotic disorders, potentially related to the underlying chronic N-methyl-D-aspartate receptor (NMDAR) dysfunction, and a higher risk of suffering from schizophrenia particularly in those genetically susceptible, or genetically predisposed ketamine abusers. With ketamine infusion rises as a emerging hope as an acute treatment for depression and suicidality under the shadow of unknown longer term psychotomimetic effects peculiarly amongst repeated or chronic use, the current case-control study aims to investigate: a) if repeated or chronic ketamine use is associated with an increased risk of psychosis by comparing those ketamine abusers with and without psychosis, and to those non-ketamine-using drug abusers with psychosis; and b) if genetic predisposition from single nucleotide polymorphisms are associated with risk of psychosis in ketamine abusers.

Inclusion Criteria:

• Age: 12 - 65 years old
• Able to read and communicate in English and/or Chinese
• Able to give informed consent
• Self-reported to have psychoactive substance use continuously for ≥3 month
• At least one positive urine toxicology result showing the reported psychoactive substance being used

Exclusion Criteria:

• Age <12 years old
• Unable to read English or Chinese
• Unable to give informed consent
• Had been diagnosed to have Intellectual Disabilities (DSM-5) or Mental Retardation (ICD-10, F70-73)
• Had been diagnosed to have primary psychosis prior to the use of any psychoactive substances, including alcohol
• Had been diagnosed to have "bipolar and related disorder" prior to the use of any psychoactive substances, including alcohol
• Had been diagnosed to have "major depressive disorder with psychotic features" prior to the use of any psychoactive substances, including alcohol
• Had been diagnosed to have "psychotic disorder due to another medical condition" (DMS-5)
• Self-reported to have abstained from any psychoactive substance use continuously for ≥12 months AND with negative urine toxicology result at the time of recruitment/ intake at the psychiatric services as recorded on case notes

ketamine abuser and non-ketamine-using drug abusers