In a patient with hyponatremia and normal lab findings, which medication is most likely causing his condition?

In this scenario, the correct choice is based on the association of certain medications with the development of hyponatremia, particularly in the context of selective serotonin reuptake inhibitors (SSRIs) like sertraline. Sertraline has been well-documented in psychiatric literature to potentially cause hyponatremia, especially in elderly patients or those on multiple medications due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH).

When prescribed, SSRIs can lead to the retention of water and dilution of serum sodium levels, resulting in hyponatremia. This side effect should be monitored, especially in patients with risk factors such as advanced age, dehydration, or concurrent medications that may exacerbate this condition.

In contrast, while other medications such as fluoxetine (another SSRI), venlafaxine (a serotonin-norepinephrine reuptake inhibitor), and buspirone (an anxiolytic) can have various side effects, they are generally less commonly associated with hyponatremia compared to sertraline. As a result, sertraline stands out as the most likely candidate to be responsible for the patient's condition, given the clinical context.