Which medication is a 5HT-2A receptor antagonist used to treat serotonin syndrome?

• A. Cyproheptadine (Periactin) - 5HT-2A receptor antagonist
• B. Dantrolene
• C. Bromocriptine
• D. Haloperidol

Answer: (A)

Treating serotonin syndrome hinges on blocking the excessive serotonin effects, especially at the 5-HT2A receptor, which drives many of the agitation, hyperreflexia, clonus, and hyperthermia seen in this condition. Cyproheptadine is an antihistamine with strong antiserotonergic action and acts as an antagonist at the 5-HT2A receptors. By blocking these receptors, it directly counteracts the receptor-mediated symptoms of serotonin excess, making it the most appropriate choice among the options.

The other drugs don’t target this serotonergic overactivity in the same way. Dantrolene works on muscle calcium release and is used for malignant hyperthermia or neuroleptic malignant syndrome, not serotonin toxicity. Bromocriptine is a dopamine agonist and does not address the serotonin surge. Haloperidol is a dopamine antagonist and, in this context, can worsen the situation or obscure the underlying issue, so it isn’t used to treat serotonin syndrome.