Finasteride lowers a potent form of testosterone that drives hair-follicle shrinkage and prostate growth. The strongest evidence shows it slows and often partly reverses male pattern hair loss and eases enlarged-prostate urinary symptoms while lowering related complications. Most men tolerate it well, but a minority report sexual, mood, or breast effects; benefits last only while taken. (Full Review)

Protocol

Hair Loss

1 mg daily

Oral, once daily; often combined with topical minoxidil

Enlarged Prostate

5 mg daily

Oral, once daily; often with an alpha-blocker

Timing

Same time daily

Flexible; single daily dose is sufficient. Some take it at night

Time to effect

Hair Regrowth

3–6 months

Visible benefit begins

Prostate Relief

6–12 months

Urinary symptoms ease

Peak Hair Effect

12–24 months

Maximum hair benefit

Benefits

High: Reverses and prevents male pattern hair loss; improves enlarged-prostate urinary symptoms; reduces acute urinary retention and need for prostate surgery

Medium: Reduces overall prostate cancer detection

Low: Psychological and quality-of-life benefit from hair retention

Speculative: Direct healthspan extension via long-term DHT suppression

Contraindications

Pregnancy or possible pregnancy

Children

Known hypersensitivity

Key Interactions

Strong CYP3A4 inhibitors (ketoconazole, ritonavir, clarithromycin)

Strong CYP3A4 inducers (rifampin, carbamazepine)

DHT-blocker supplements (saw palmetto, pygeum, stinging nettle)

Dutasteride or topical anti-androgens

Significant liver impairment

Risk & Side Effects

High: Sexual dysfunction; PSA suppression masking cancer screening; reproductive and teratogenic risk

Medium: Gynecomastia; depression and mood changes

Low: Increased risk of high-grade prostate cancer

Speculative: Post-finasteride syndrome

Monitoring

Marker	Target	Why
Prostate-specific antigen (PSA)	Stable; double on-treatment values, within age-appropriate limits	Screens for prostate cancer; finasteride halves it
Total testosterone	~300–1000 ng/dL	Confirms testosterone is preserved; often rises slightly
Dihydrotestosterone (DHT)	Reduced ~60–70% from baseline	Confirms the drug is biologically active
Liver enzymes (ALT/AST)	Within standard laboratory limits	Finasteride is metabolized by the liver

Cadence: Baseline, then ~4 weeks, 3 months, and 6 months; thereafter every 6–12 months. PSA at baseline, 6 months, and annually.

Qualitative Assessment

Sex drive (libido) and erectile and ejaculatory function
Mood, motivation, and anxiety levels
Hair density and shedding, tracked with standardized monthly photographs
Urinary flow, urgency, and nighttime urination

Finasteride for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment