CNS Pharmacology USMLE Step 1 Practice Question
A 24-year-old man with schizophrenia treated with risperidone 4 mg daily for 1 year presents with erectile dysfunction and galactorrhea. His girlfriend also reports amenorrhea for 3 months. Physical examination reveals bilateral nipple discharge expressible on palpation. Vital signs: BP 118/76, HR 88, RR 16, Temp 37°C, SpO2 98%. Serum prolactin is 85 ng/mL (normal: 4–15 ng/mL); testosterone, TSH, and thyroid function are normal. MRI of the pituitary shows no adenoma. He denies chest pain or visual changes. Which mechanism explains this medication adverse effect?
Answer choices
- AIncreased thyroid-stimulating hormone from antipsychotic-induced hypothyroidism
- BSerotonin 5-HT2A receptor antagonism promoting prolactin release
- CHistamine H1 receptor blockade in the hypothalamus
- DDopamine D2 receptor blockade in the tuberoinfundibular tract relieving prolactin inhibitionCorrect answer
- EDirect stimulation of lactotroph cells in the pituitary
- FAntipsychotic-induced increase in thyrotropin-releasing hormone stimulating prolactin secretion
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