The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common cause of euvolemic hyponatremia in hospitalized patients. The syndrome is an osmoregulatory disorder, consisting of hyponatremia, decreased serum osmolality, inappropriately elevated urine osmolality, excessive urine sodium in a patient who is euvolemic.

The selective serotonin reuptake inhibitors (SSRIs), a frequently prescribed class of antidepressant, have been well reported to cause SIADH. This often poses a clinical challenge to psychiatrists in the consultation liaison and psychogeriatrics setting, where patients are at a higher risk of developing hyponatremia. Other classes of antidepressants should be considered if clinically indicated.

To report an elderly psychiatric patient who was diagnosed with SIADH induced by duloxetine, which belongs to a class of antidepressant known as the serotonin-norepinephrine-reuptake inhibitors (SNRIs).

Patients developing antidepressants induced SIADH present a clinical dilemma to clinicians. Future studies evaluating the incidence of SIADH attributed to the different classes of antidepressants would be helpful to clinicians. Close monitoring of sodium level should be considered when antidepressant therapy is started for patients who are at high risk of developing SIADH.