A 67-year-old man starting citalopram for treatment of depression. Which adverse reaction is most likely to be observed when taking or using the medication?

• A. Hypotension
• B. QT prolongation
• C. Weight gain
• D. Sedation

Answer: (B)

Citalopram can cause QT interval prolongation, and this risk is higher in older adults. The QT interval reflects the time for ventricular depolarization and repolarization; when it lengthens, the heart is more prone to dangerous rhythms like torsades de pointes. In someone who is 67, starting citalopram, this makes QT prolongation the most likely clinically observed adverse effect, especially if there are electrolyte disturbances or other drugs that also prolong the QT interval.

Other common antidepressant-related issues like hypotension, weight gain, or sedation are less typical with citalopram, particularly at standard doses, which is why QT prolongation stands out as the most likely adverse reaction in this scenario. If there are risk factors (electrolyte disturbances, concomitant QT-prolonging meds, baseline long QT), an ECG may be considered and dosing adjusted to minimize risk.