Which OTC cough suppressant has potential interaction with MAO inhibitors leading to serotonin syndrome?

• A. Dextromethorphan
• B. Diphenhydramine
• C. Guaifenesin
• D. Chlorpheniramine

Answer: (A)

Serotonin syndrome risk arises when a drug that boosts serotonin in the brain is used with an MAO inhibitor, which prevents breakdown of serotonin. Dextromethorphan has serotonergic activity and can increase serotonin levels by interfering with reuptake and other pathways. When combined with MAO inhibitors, serotonin can accumulate and trigger serotonin syndrome, which can present with agitation, rapid heart rate, high blood pressure, fever, muscle rigidity or tremors, and altered mental status.

Other common OTC cough suppressants don’t share this serotonergic interaction with MAO inhibitors. Diphenhydramine and chlorpheniramine are antihistamines with anticholinergic effects rather than major serotonergic effects. Guaifenesin is an expectorant with no meaningful serotonergic activity.