Which of the following is a symptom of serotonin syndrome?

• A. Hyperreflexia
• B. Hyporeflexia
• C. Bradypnea
• D. Hypotension

Answer: (A)

Serotonin syndrome shows neuromuscular hyperactivity driven by excessive serotonergic stimulation, so signs like hyperreflexia (often with clonus) are classically seen after exposure to serotonergic agents. The heightened reflex response reflects increased excitability in spinal and brainstem pathways from elevated serotonin levels, and clonus may accompany the hyperreflexia, especially with agitation or tremor.

The other possibilities don’t fit as well. Hyporeflexia would indicate reduced reflexes, which isn’t typical of serotonin syndrome. Bradypnea isn’t a defining feature and is not a hallmark of this syndrome— autonomic changes can occur, but breathing rate isn’t the key distinguishing sign. Hypotension is less characteristic, as patients often become tachycardic and hypertensive rather than hypotensive.

So hyperreflexia stands out as the most characteristic symptom.