Anxiolytic treatment but not anxiety itself causes hyponatremia among anxious patients

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The aim of the study was to define whether anxiety itself or only the treatment with anxiolytic medication is risk factor for hyponatremia and overhydration. A case–control study of patients with a diagnosis of anxiety who received a selective serotonin reuptake inhibitor (SSRI). Serum sodium, urea to creatinine ratio, and odds ratio (OR) of hyponatremia and overhydration before initiation of treatment were compared to those of a control group of participants. Laboratory tests were also examined for changes following treatment with an SSRI. All blood tests were conducted from January 1, 2001 until December 31, 2017. Subjects were selected from a large electronic database, insuring 2 million Israelis. A total of 7211 patients with a diagnosis of anxiety who have received a prescription for an SSRI were identified; 3634 were excluded mostly due to other conditions that could cause hyponatremia, and 3520 participants were included in the case group. The control group consisted of 6985 age and gender matched participants who did not have a diagnosis of anxiety or any other exclusion criteria. Mean serum sodium levels were elevated in cases before the initiation of SSRIs; sodium: case 139.3 (137.3–141.3), control 139.2 (137.06–141.26) mmol/L (P = .01). The OR of hyponatremia was 0.89 for the case group (P = .004). Treatment with SSRIs decreased mean serum sodium (139.3–139.1 mmol/L; P = .0001) and increased by 50% the rate of hyponatremia (2.6–3.9% P = .024). It is the use of SSRIs and not anxiety itself that causes hyponatremia among anxious patients.