Which medication is a dopamine agonist used to treat prolactinomas?

Bromocriptine is a dopamine agonist commonly used in the treatment of prolactinomas, which are tumors that produce an excess of prolactin, leading to hyperprolactinemia. The mechanism by which bromocriptine works involves stimulating dopamine receptors, specifically the D2 subtype, which inhibits prolactin secretion from the anterior pituitary gland. As a result, this medication effectively reduces prolactin levels and can lead to a decrease in tumor size and alleviation of symptoms associated with prolactin excess, such as galactorrhea and menstrual irregularities.

In contrast, the other medications listed, including haloperidol, chlorpromazine, and clozapine, are antipsychotic agents. They primarily block dopamine receptors and can increase prolactin levels due to their antagonist activity at the D2 receptors. While they have important roles in treating various psychiatric disorders, they would be counterproductive and inappropriate for managing prolactinomas or hyperprolactinemia. Therefore, bromocriptine stands out as the correct choice for treating conditions related to elevated prolactin caused by prolactin-secreting tumors.