Finasteride (Propecia) for Androgenetic Alopecia — Skin & Hair
5-alpha reductase type II inhibitor FDA-approved for male pattern hair loss, reducing DHT by approximately 70%.
Overview
Finasteride is a synthetic 4-azasteroid that selectively inhibits type II 5-alpha reductase, the enzyme responsible for converting testosterone to dihydrotestosterone (DHT) in prostate tissue, scalp hair follicles, and other androgen-sensitive tissues. At the 1 mg daily dose (Propecia), finasteride reduces serum DHT by approximately 70% while minimally affecting testosterone levels. DHT is the primary androgen responsible for miniaturization of hair follicles in androgenetic alopecia (AGA), and its reduction halts further hair loss in 83% of men and promotes visible hair regrowth in 66% over 2 years. The landmark Kaufman et al. (1998) study demonstrated significant improvements in hair count, weight, and appearance versus placebo at 1 and 2 years. Long-term data from the 5-year Rossi study showed continued benefit with minimal side effects. A 5 mg dose (Proscar) is FDA-approved for benign prostatic hyperplasia. Finasteride's role in men on TRT is particularly important, as exogenous testosterone increases the substrate available for conversion to DHT, potentially accelerating hair loss in genetically susceptible individuals.
Indications
- FDA-approved: Male pattern hair loss (androgenetic alopecia) — 1 mg
- FDA-approved: Benign prostatic hyperplasia (BPH) — 5 mg
- Off-label: Female pattern hair loss (postmenopausal women only)
- Off-label: Hirsutism in women (with contraception)
- Off-label: DHT management during TRT
Mechanism of Action
Finasteride selectively and competitively inhibits type II 5-alpha reductase, the predominant isoform in hair follicles and prostate
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Finasteride | 1 mg | Once daily | FDA-approved dose for androgenetic alopecia (Propecia) |
| Finasteride | 5 mg | Once daily | FDA-approved dose for BPH (Proscar) |
| Finasteride | 0.25% | Once daily to scalp | Compounded topical — lower systemic exposure, emerging evidence |
Evidence Grade
GRADE A
Safety & Contraindications
- Sexual side effects: decreased libido (1.8%), erectile dysfunction (1.3%), ejaculatory disorder (1.2%) — rates from RCTs
- Post-finasteride syndrome (PFS): persistent sexual and neurological symptoms after discontinuation — controversial, under FDA review
- Depression and anxiety reported in some users
- Contraindicated in women of childbearing potential — teratogenic (ambiguous genitalia in male fetus)
- Pregnant women should not handle crushed/broken tablets (transdermal absorption)
- Reduces PSA by approximately 50% — adjust PSA values accordingly when screening for prostate cancer
- Gynecomastia (rare, <1%)