An oral medication that lowers the hormone driving inherited pattern hair loss. In men it adds hair and largely halts further visible loss while taken; in women it has not shown benefit at the male dose. A minority of men report sexual or breast effects, usually resolving after stopping. It roughly halves the prostate screening marker. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Prostate-specific antigen, total | Below 1.0 ng/mL under age 50; below 1.5 ng/mL age 50–59 | Establishes the pre-drug reference that treatment will suppress |
| Serum dihydrotestosterone | 30–85 ng/dL untreated; 65–70% below the individual's own baseline on treatment | Confirms the drug is actually suppressing its target |
| Total testosterone | 500–900 ng/dL | Detects the modest rise expected once conversion is blocked, and flags unrelated deficiency |
| Oestradiol | 20–30 pg/mL by liquid chromatography–mass spectrometry | Tracks the diverted conversion route implicated in breast tenderness and gynecomastia |
| Alanine aminotransferase | 10–26 U/L for men; 10–19 U/L for women | Screens the hepatic route by which finasteride is cleared |
| Ferritin | 70–100 ng/mL where hair growth is the concern | Excludes iron-deficient shedding being mistaken for drug non-response |
| Thyroid-stimulating hormone | 0.5–2.0 mIU/L | Excludes thyroid-driven hair loss, which androgen blockade cannot address |
| Target-area hair density | No established universal target; track change from the individual's own baseline, with any increase counted as response | The only direct measure of the outcome being sought |
Cadence: Review at 12 weeks for tolerability and mood; hormone and liver testing at 6 months, then annually. Prostate-specific antigen annually from age 40 and at any new urinary symptom. Photography at 6 and 12 months, then yearly.