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Objective: Hyponatremia (serum sodium concentration [Na+] <136 mEq/L) is a potentially life-threatening condition often found chronically in patients with psychotic disorders. Vasopressin antagonists have recently been shown in short-term studies to correct hyponatremia in diverse patient populations, including individuals with both psychosis and idiopathic hyponatremia. However, the safety and efficacy of long-term administration of vaptans is only beginning to be investigated. The objective of this study was to assess whether one of the vaptans, specifically tolvaptan, maintained its safety and efficacy over a prolonged period in patients with psychosis and chronic idiopathic hyponatremia., Methods: SALTWATER was a multicenter, open-label extension of the Study of Ascending Levels of Tolvaptan in Hyponatremia. Of the 111 patients enrolled in SALTWATER, eight were patients with both psychosis and idiopathic hyponatremia. These eight subjects provided a total of 7,406 patient days of exposure to oral tolvaptan., Results: Mean serum [Na+] in the eight psychotic patients increased from 131.6 mEq/L at baseline to >135 mEq/L throughout the observation period (p<0.05 versus baseline at most points). No drug-related adverse events led to study discontinuation., Conclusions: Chronic hyponatremia is known to have deleterious effects on the quality of life for many patient groups. These preliminary results suggest that oral tolvaptan provides rapid, effective, and safe treatment of chronic hyponatremia in patients with psychotic disorders and that the effect is safely sustained over long periods of time. These findings represent an important step forward in treating a significant unmet need in psychotic populations.