Which class of medications commonly causes hyperprolactinemia by blocking dopamine D2 receptors?

• A. Dopamine antagonists (antipsychotics).
• B. Serotonin reuptake inhibitors.
• C. Beta blockers.
• D. ACE inhibitors.

Answer: (A)

Dopamine normally keeps prolactin levels in check by acting on D2 receptors in the pituitary's tuberoinfundibular pathway. When these D2 receptors are blocked, the inhibitory influence on lactotrophs is removed, leading to increased prolactin release and hyperprolactinemia. This is a classic effect of dopamine antagonists, also known as antipsychotics, which block D2 receptors to provide their therapeutic CNS effects. That blockade in the pituitary explains the common side effects like galactorrhea, menstrual irregularities, and infertility.

The other options don’t explain hyperprolactinemia through direct D2 receptor blockade. Serotonin reuptake inhibitors can raise prolactin via serotonin pathways, but not by blocking D2 receptors. Beta blockers and ACE inhibitors don’t influence prolactin through this mechanism.