Which substance is used to treat serotonin syndrome?

• A. Diazepam
• B. Naloxone
• C. Physostigmine
• D. Cyproheptadine

Answer: (D)

Serotonin syndrome is driven by an excess of serotonin signaling, so treatment aims to counteract that effect by blocking serotonin receptors while stopping the triggering agent. Cyproheptadine is a nonselective serotonin receptor antagonist, particularly blocking 5-HT receptors such as 5-HT2A, which helps reduce the CNS and autonomic hyperactivity seen in the syndrome. This direct anti-serotonergic action makes it the drug of choice for mild-to-moderate cases.

Diazepam can help with agitation and muscle activity as part of supportive care, but it doesn’t counteract serotonin excess itself. Naloxone targets opioid toxicity, not serotonin syndrome. Physostigmine addresses anticholinergic toxicity and is not appropriate for serotonin excess. Therefore, cyproheptadine best addresses the underlying issue.