hyponatremia is a common in older and hospitalized patients, often caused by the syndrome of inappropriate antidiuretic hormone secretion (SIADH). This study compares the efficacy and safety of tolvaptan versus fluid restriction in patients with hyponatremia and SIADH. an observational cohort study was conducted with 186 patients with hyponatremia (Na+ < 135 mmol/L) due to SIADH, treated at the Hospital Universitario de Pontevedra between 2015 and 2022. Of these, 86 were treated with tolvaptan (mean dose of 7.5 mg) and 100 with fluid restriction (1 liter of fluids per day). The primary endpoint was the normalization of sodium levels (Na ≥ 135 mmol/L). tolvaptan was more effective than fluid restriction in correcting hyponatremia, increasing plasma sodium from 125.09 to 135.69 mmol/L in 4 days, compared to an increase from 126.44 to 130.5 mmol/L in 8 days with fluid restriction (p < 0.001). Mortality at 60 days was lower in the tolvaptan group (12.8 % vs. 32.8 %, p < 0.003). However, tolvaptan showed higher risks of sodium overcorrection (10.46 %) and polyuria (5.81 %), while fluid restriction was associated with greater dehydration, headache, and cramps. tolvaptan corrects hyponatremia more quickly and effectively than fluid restriction, although with a higher risk of overcorrection and polyuria, and is associated with lower 60-day mortality.