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Introduction Psychogenic or primary polydipsia characterized by excessive thirst and compulsive water drinking is a common problem among psychiatric populations, affecting 6% to 20% of patients. It is frequent in chronic psychiatric diseases, particularly schizophrenia. We report a patient with excessive thirst and diagnosed as PIP syndrome. Case A 54-year-old, married, female patient had normal vital signs. She has excessive water intake (10–12 L/day). She did not have edema, signs of dehydration or fever. The neurological examination, CT, MRI, and EEG was normal. The laboratory tests were normal. She had started using sertraline 100 mg, 7 months ago due to anxiety disorder. There is not any disease except the anxiety disorder, which is in remission due to the treatment. A total of, 2 μg desmopressin I.M. is applied in fluid restriction test. The urine density is determined as 1.008 mg/dL initially, 1.011 mg/dL one hour later, and 1.013 mg/dL two hours later in the urinary test. The diagnosis is psychogenic polydipsia (primary) according to patient history, the clinical examination, and the test results. The patient is recommended to continue the sertraline 100 mg treatment, and also assigned with fluid restriction behaviour. Conclusion Since excess water intake periods are correlated with psychotic exacerbations; psychosis and polydipsia might have similar physiopathologic mechanisms. Polydipsia might be due to anti-cholinergic side effect of some psychiatric drugs. The physiopathology of the polydipsia and polyuria is not totally enlightened in the psychiatric disorders. In some cases, the fluid intake occurs completely voluntary. Therefore, we decided to present this case. Disclosure of interest The authors have not supplied their declaration of competing interest.