Finasteride blocks the enzyme that converts testosterone into a stronger hormone acting on the prostate and hair follicles. Evidence is strong for slowing male pattern hair loss and shrinking an enlarged prostate. No study has shown it extends life. Sexual side effects are firmly established, and the drug halves the blood marker used to screen for prostate cancer. (Full Review)

Protocol

Standard hair-loss protocol

1 mg orally once daily

Taken indefinitely; the reference regimen in dermatology practice worldwide

Standard prostate protocol

5 mg orally once daily

Frequently combined with an alpha-blocker in men with enlarged glands

Best time of day

Timing is clinically irrelevant

Effect persists across the full day; food does not affect absorption

Time to effect

Hair density

6–12 months

Visible density changes; maximum effect around two years

Hair shedding

3 months

Shedding usually slows, before regrowth is visible

Prostate symptoms

~6 months

Symptom relief follows as the gland shrinks

Benefits

High: Preservation and regrowth of scalp hair; reduced progression of benign prostatic enlargement; lower overall prostate cancer incidence (conflicted)

Medium: Reduced prostate cancer mortality with prolonged exposure; reduction of excess facial and body hair growth in women

Low: Improved plasma lipid profile (conflicted); reduced prostate-related bleeding

Speculative: Slowed systemic ageing through lowered androgen signalling

Contraindications

Women who are pregnant, may become pregnant, or are breastfeeding

Children and adolescents under 18 years

Documented hypersensitivity to finasteride or other 4-azasteroid compounds

Severe liver impairment (Child-Pugh Class C)

Active major depressive disorder or a history of suicidal ideation, unless under close psychiatric supervision

Men actively attempting conception who already have a low sperm count

Key Interactions

Prescription drug interactions: Strong CYP3A4 inhibitors (ketoconazole, ritonavir, clarithromycin) and inducers (rifampicin, carbamazepine)

Alpha-blockers: Additive dizziness and low blood pressure on standing (doxazosin, tamsulosin)

Over-the-counter medications: No clinically significant interactions documented

Supplement interactions: High-dose biotin distorts prostate-specific antigen assays

Supplements with additive effects: Saw palmetto, pygeum, beta-sitosterol, pumpkin seed oil

Other intervention interactions: Testosterone replacement; dutasteride is redundant

Risk & Side Effects

High: Sexual dysfunction; increased detection of high-grade prostate cancer (conflicted); suppression of prostate-specific antigen; teratogenic harm to a male fetus

Medium: Gynecomastia and breast tenderness; depressive symptoms and self-harm (conflicted); new-onset type 2 diabetes

Low: Persistent symptoms after discontinuation (conflicted); impaired semen quality

Speculative: Male breast cancer

Monitoring

Marker	Target	Why
Total prostate-specific antigen (PSA)	Below 2.5 ng/mL after doubling the measured value	Detects prostate cancer despite drug-induced suppression
Total testosterone	600–900 ng/dL	Confirms testosterone is rising rather than falling, as expected
Oestradiol (sensitive assay)	20–30 pg/mL	Rising oestradiol accompanies breast tenderness and enlargement
Hemoglobin A1c	Below 5.4%	Detects the modest excess risk of new-onset type 2 diabetes
Low-density lipoprotein cholesterol	Below 100 mg/dL, or below 70 mg/dL with cardiovascular risk	Tracks the disputed lipid effect in either direction
Alanine aminotransferase (ALT)	10–26 U/L for men, 10–19 U/L for women	Confirms hepatic clearance is unimpaired, since metabolism is entirely liver-based

Cadence: Baseline panel before the first tablet, then three months, six months, twelve months, and every twelve months indefinitely; the six-month draw serves as the new prostate-specific antigen anchor.

Qualitative Assessment

Standardised scalp photographs under identical lighting at baseline, six months and twelve months
Libido and erectile quality, scored rather than recalled
Mood, motivation and emotional range, tracked monthly for the first six months
Sleep depth and morning restedness
Cognitive clarity and word-finding
Urinary stream force, nocturnal frequency and sense of complete emptying, for the prostate indication

Finasteride for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment