Patients with psychosis have activation of the hypothalamic-pituitary-adrenal (HPA) axis during the acute phase of the psychosis. Whether this has any morphological consequences for the pituitary gland is currently unknown.

To examine pituitary volume variation in people at different stages of psychotic disorder.

Pituitary volume was measured using 1.5 mm, coronal magnetic resonance images in 24 people with first-episode psychosis, 51 with established schizophrenia and 59 healthy controls.

Compared with the control group, the people with first-episode psychosis had pituitary volumes that were 10% larger, whereas those with established schizophrenia had pituitary volumes that were 17% smaller. In both of the groups with psychosis, there was no difference in pituitary volume between those receiving typical antipsychotic drugs and those receiving atypical antipsychotics.

The first episode of a psychosis is associated with a larger pituitary volume, which we suggest is due to activation of the HPA axis. The smaller pituitary volume in the group with established schizophrenia could be the consequence of repeated episodes of HPA axis hyperactivity.