A 30-year-old female-to-male transgender patient on testosterone therapy has a side effect that may be addressed with an additional medication. Which drug could be prescribed?

• A. Tamoxifen
• B. Spironolactone
• C. Progestin
• D. Finasteride

Answer: (D)

Testosterone therapy can lead to androgenic alopecia because the hormone is converted in the scalp to dihydrotestosterone (DHT), which drives miniaturization of hair follicles in genetically susceptible individuals. Finasteride works by inhibiting 5-alpha-reductase, the enzyme that converts testosterone to DHT. By lowering DHT levels, it reduces ongoing follicle miniaturization and can help slow or reverse scalp hair loss in many patients.

This makes finasteride the best choice here because it directly targets the DHT-mediated process causing the side effect. The other options don’t address this mechanism: tamoxifen modulates estrogen receptors, spironolactone is an antiandrogen mainly used to reduce androgen effects like hirsutism in other contexts, and progestin doesn’t have a role in treating DHT-driven hair loss.