Finasteride

Propecia · Proscar

Anti-Androgen HRT TRT Oral FDA/EMA Label

Half-life

6 hr

Time to Peak

1.5 hr

Steady State

~2 days

Bioavailability

65%

Dose Range

1–5 mg

Frequency

Daily

Overview

Type II 5-alpha-reductase inhibitor. Blocks conversion of testosterone to DHT. Used for hair loss (1 mg/day) and BPH/prostate (5 mg/day). In transfem HRT, used to reduce DHT-mediated effects (body/facial hair, scalp hair loss). In TRT, used to mitigate androgenic side effects. DHT suppression persists beyond plasma clearance due to tight enzyme binding. Category X -- teratogenic.

Mechanism of Action

Selective inhibitor of type II 5-alpha-reductase. Reduces serum DHT by ~70% at 5 mg/day without affecting testosterone levels directly.

Dosing Information

Route	Dose Range	Half-life	Tmax	Frequency
Oral	1–5 mg	6 hr	1.5 hr	Daily

Used in Regimens

1 regimen

Transmasculine T + Finasteride (Hair Preservation)

Testosterone cypionate standard transmasculine protocol with finasteride added for androgenic alopecia management. Finasteride inhibits 5-alpha-reductase, reducing DHT. For transmasculine patients experiencing or at high risk of male-pattern hair loss on testosterone.

Finasteride 1mg/day — transmasc-specific protocol.

hrt_masc

Ancillary

Data Sources

FDA Label Proscar (finasteride 5 mg) FDA Prescribing Information
FDA Label Propecia (finasteride 1 mg) FDA Prescribing Information

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