ABSTRACT
The use of psychotropic drugs has been frequently associated with hyponatremia, which is defined as a serum sodium level of less than 136 mEq/l. The main cause in the psychiatric population is the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Age, female sex and polypharmacy are risk factors for hyponatremia. In psychiatric patients, the symptomatology caused by hyponatremia may be confused with the mental illness itself, delaying its diagnosis. Early symptoms are nausea, vomits, anorexia, headaches, weakness, irritability, agitation, lethargy, confusion and cramps. The risk of hyponatremia increases with the use of several psychiatric drugs associated with SIADH. This complication is more often diagnosed at the first weeks of treatment. The first step of treatment is to determine the real level of hypoosmolality by measuring plasmatic osmolality. A urinary osmolality equal to or higher than 100 mOsm/kg combined with an elevated concentration of urinary sodium may lead to the diagnosis of SIADH. The main treatment for drug-caused hyponatremia is medication monitoring and normalization of extracellular liquid volume. In most cases this is achieved by discontinuing medication and restricting fluid intake.