Schizophrenia is a serious, chronic and relapsing mental illness with a worldwide lifetime prevalence of about one percent. An uncommon but serious complication of psychotic illness is polydipsia, the intake of more than three litres of fluids per day. Although the exact reason for any one person developing polydipsia is unclear, effective treatment is essential as if untreated, such a high intake of fluids can lead to hyponatraemia which in turn can lead to coma or even death. It is estimated that between 6% and 17% of psychiatric inpatients suffer from polydipsia, and even if this is an over estimate it is a common and serious enough condition to merit clinical concern.
We systematically searched and evaluated randomised controlled trials investigating the effectiveness of drug treatment for polydipsia. We found two short trials (n=17, duration 3-6 weeks) that were too small and short to be informative. Data reporting was also poor with no pre crossover data available for analysis. The only data available were for adverse effects and neither the active treatments nor placebo produced any serious side effects. The studies did not report any useful data on measures of polydipsia, physical symptoms secondary to increased fluid intake, mental state, general functioning or economic outcomes.
Clinicians hoping to treat people with psychosis-related polydipsia are unable to gain any useful information from these trials and treatment of any sort might only be informative within a well-designed study. More research is needed and these two trials, although unable to provide much data, do show this type of research is possible.