Which of the following is a dopamine receptor antagonist?

• A. Chlorpromazine
• B. Sumatriptan
• C. Methylphenidate
• D. Promethazine

Answer: (A)

Dopamine receptor antagonism, especially blocking D2 receptors, is the hallmark of classic antipsychotics. Chlorpromazine, a phenothiazine antipsychotic, works by antagonizing dopamine D2 receptors in key brain pathways, which helps reduce psychotic symptoms. Its action on D2 receptors is the primary reason it’s considered a dopamine receptor antagonist.

Sumatriptan acts on serotonin receptors (5-HT1B/1D) to treat migraines, not dopamine receptors. Methylphenidate increases dopamine and norepinephrine in the synapse by blocking reuptake, so it enhances dopaminergic signaling rather than antagonizes it. Promethazine is mainly used for its antihistamine effects (with antiemetic and sedative properties) and is not defined by dopamine receptor antagonism as its primary action.