Electroconvulsive therapy (ECT) is one of the oldest neuromodulation treatments still used in psychiatry. Only case reports and open label non-randomized studies have been published of ECT in clozapine-resistant schizophrenia patients. The purpose of this trial is to study the efficacy and cognitive effects of add-on ECT treatment (10-course) in schizophrenia patients taking clozapine.

Inclusion Criteria:

• diagnosis of schizophrenia or schizoaffective disorder
• treatment-resistant to clozapine
• age 18 - 64 years
• capacity and willingness to give informed consent

Exclusion Criteria:

• serious somatic illness
• progressive neurological illness, recent brain damage or sequela of serious brain damage
• ECT less than 3 months prior to this trial