Finasteride
B
Finasteride
Finasteride
Oral
Finasteride is a selective type II 5α-reductase inhibitor that reduces DHT levels by approximately 65-70% by blocking the conversion of testosterone to dihydrotestosterone. Used as adjunctive therapy in transfeminine HRT, primarily for hair loss and excessive body hair.
Mechanism
Section titled “Mechanism”Finasteride selectively inhibits type II 5α-reductase (primarily found in hair follicles and prostate), reducing serum DHT by ~65-70% while having virtually no effect on testosterone levels.
Compared to dutasteride, finasteride inhibits only one isoform, resulting in less DHT reduction but also potentially fewer side effects.
Dosing
Section titled “Dosing”| Indication | Dose | Notes |
|---|---|---|
| Hair loss (adjunct to HRT) | 1 mg/day | Combined with HRT regimen |
| Alternative dose | 5 mg/day | Some clinicians use higher doses, but additional benefit is unclear |
- Start at 1 mg/day, the standard hair loss dose
- 5 mg tablets (Proscar) are often cheaper and can be quarter-split
- Onset typically requires 3-6 months
Brands & Availability
Section titled “Brands & Availability”| Brand | Strength | Notes |
|---|---|---|
| Propecia | 1 mg | Hair loss indication |
| Proscar | 5 mg | BPH indication, can be split |
| Generics | 1 mg / 5 mg | Widely available globally |
Monitoring
Section titled “Monitoring”- T: Continue routine HRT monitoring every 3 months
- DHT (optional): Can confirm 5αRI effect
- Liver function: Finasteride rarely causes hepatic injury; no additional monitoring usually needed
- PSA: Finasteride reduces PSA by ~50%; inform your doctor if PSA is being tested
Contraindications
Section titled “Contraindications”- Finasteride allergy
- Severe hepatic impairment
- Pregnant partners must not handle crushed/broken tablets (teratogenic to male fetuses — typically not relevant in trans HRT context)