Objective: The aim of this study was to determine the prevalence of polydipsia-hyponatremia among patients with schizophrenia in an Asian mental hospital.

Methods: Seven hundred and twenty-eight inpatients with schizophrenia were assessed for polydipsia-hyponatremia using case notes reviews, specific gravity of urine, normalised diurnal weight gain, and serum sodium levels.

Results: One hundred and three (13.8%) patients had polydipsia, 30 (4.1%) had polydipsia-hyponatremia and 14 (1.9%) had a history of water intoxication. Eight of the 30 patients were receiving carbamazepine, three were on tricyclic antidepressants and two had diabetes mellitus and were on sulfonylureas.

Conclusions: The prevalence of water intoxication among polydipsic patients was low compared to Western studies. This could be due to different methods of assessing polyuria, or ethnic differences and/or the prohibition of smoking in our patients. Certain medications might have also contributed to hyponatremia.