Acetazolamide for Treatment Resistant Schizophrenia

Inclusion Criteria:

* Written informed consent.
* Both genders, ages 18-55 years (older patients may not tolerate high ACZ dose).
* PANSS total score \> 60 and Score \> 4 on one or more items of the 'positive' syndrome items (P1-P7), following treatment at therapeutic doses for 6 weeks with different APDs on 2 occasions.
* Stable dose of antipsychotic drug (APD) for \> 1 month, continued throughout the study.
* Not participating in another randomized controlled clinical trial (RCT).

Exclusion Criteria:

* Substance abuse in the past month/dependence past 6 months with the exception of methadone prescribed for opiate withdrawal.
* History or current medical/neurological illnesses that may lead to unstable course, e.g., epilepsy.
* Pregnancy.
* Acetazolamide (ACZ) contraindications: hypersensitivity to ACZ; history of renal hyperchloremic acidosis; Addison's disease/adrenal failure; chronic closed angle-closure glaucoma.
* Current or prior treatment with ACZ or history of hypersensitivity to ACZ.
* Intellectual disability as defined in DSM 5.