The Northwick Park "functional" psychosis study: diagnosis and treatment response.

Functional psychosis is conventionally subdivided into schizophrenia and manic depressive psychosis. Response to treatment is assumed to be a validating criterion for these diagnoses. The efficacy of pimozide (a dopamine antagonist neuroleptic), lithium, and a combination of the two was compared with that of placebo in a 4 week trial in 120 functionally psychotic patients each of whom was assessed for psychotic symptoms, manic symptoms, and depressive symptoms. The sample was subdivided into patients with predominantly elevated mood, predominantly depressed mood, and no consistent mood change. Pimozide reduced psychotic symptoms in all groups of patients. The only significant effect of lithium was to reduce elevated mood. Thus dopamine blockade seems relevant to the resolution of psychotic symptoms in all types of "functional" psychosis but the mode of action of lithium in psychotic patients concerns only mood. Application of standardised classifications of functional psychosis to these data did not change this conclusion.