Hyponatraemia occurs in 4% of schizophrenic patients. Dilutional hyponatraemia, due to inappropriate retention of water and excretion of sodium, occurs with different psychotropic medications and could lead to hippocampal dysfunction. This complication is usually asymptomatic but can cause severe problems, as lethargy and confusion, difficult to diagnose in mentally ill patients.

To describe a case of a patient with psychotropic poli-therapy, admitted three times due to hyponatremia and the pharmacological changes that improved his condition.

To broadcast the intermittent hyponatraemia and polydipsia (PIP), a not rare condition, suffered by treated schizophrenic patients and discuss its physiopathology and treatment thorough a case report.

A 56-year schizophrenic male was admitted for presenting disorganized behavior, agitation, auditory hallucinations, disorientation, ataxia, vomits and urinary retention. He was on clomipramine, haloperidol and clotiapine (recently added), quetiapine, fluphenazine and clonazepam. After water restriction his symptoms improved and he was discharged. Twenty-five days later, he was readmitted for presenting the same symptoms and after water restriction, he was discharged. Five days later, he was again admitted and transferred to the psychiatric ward.

Haloperidol, fluphenazine and clomipramine were replaced by clozapine. These changes lead him to normalize the hypoosmolality and reduce his water-voracity. Endocrinology team did not label this episode of SIADH due to its borderline blood and urine parameters.

Hyponatremia is frequent in schizophrenic patients and may have severe consequences. Therefore, a prompt recognition and treatment is warranted.

The authors have not supplied their declaration of competing interest.