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Finasteride (Propecia / Proscar) — 5α-reductase type-II inhibitor
A prescription 5α-reductase type-II inhibitor that lowers DHT to treat male pattern hair loss (1 mg, Propecia) and benign prostatic hyperplasia (5 mg, Proscar). The hair and prostate benefits are well-proven in large RCTs. The honest caveats are real and prominent: sexual side effects (erectile dysfunction, decreased libido) in a minority of men, a disputed but important 'post-finasteride syndrome' with persistent symptoms, and a depression/suicidality safety signal in pharmacovigilance data. It is NOT a longevity drug.
Prescription medication — not a dietary supplement
Finasteride is a prescription (or investigational) drug, not a supplement. It is included here for reference because people research and discuss it (often used off-label) — not as a recommendation. Take it only under a qualified clinician's supervision and only as prescribed; do not source it from grey-market vendors, where identity, purity, and dosing are unverified. The evidence below reflects its clinical trials.
What the evidence says
Finasteride doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1993–2026 with a typical study size of 1,553 participants.
Based on 319 studies · 16 meta-analyses · 239 RCTs · 1,553 total participants
Confidence
High confidenceBy outcome
Finasteride has strong, pivotal-RCT evidence for its two approved indications — durable hair retention in male pattern hair loss and reduced acute urinary retention/surgery and clinical progression in BPH — but it carries real sexual side effects, a disputed but important persistent post-finasteride syndrome, and a depression/suicidality pharmacovigilance signal, and it is not a longevity drug, so it sits mid-scale rather than higher.
242 randomised trials
92% were about Finasteride in an audit of 50 of them
Every randomised or controlled trial of Finasteride indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Sep 2026
12 trials ongoing or recruiting · 62 completed on ClinicalTrials.gov
23 of the completed trials have posted results
Registered trials show research momentum for Finasteride, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Nov 2026
Finasteride is a competitive inhibitor of 5α-reductase type II, the enzyme that converts testosterone to dihydrotestosterone (DHT). By lowering serum and scalp DHT, it treats two androgen-driven conditions.
At 1 mg/day (Propecia) it is an FDA-approved treatment for male androgenetic alopecia: the pivotal Kaufman 1998 RCT and a 5-year extension showed durable increases in scalp hair count versus progressive loss on placebo.
At 5 mg/day (Proscar) it shrinks the prostate and treats benign prostatic hyperplasia (BPH): the PLESS trial cut the risk of acute urinary retention and BPH surgery by roughly half over four years, and the MTOPS trial showed it reduced long-term clinical progression (best in combination with an alpha-blocker).
The Prostate Cancer Prevention Trial (PCPT) found finasteride reduced overall prostate-cancer prevalence by about 25% — but with an important nuance: a higher rate of high-grade (Gleason 7-10) tumors in the finasteride arm, later attributed in part to detection effects but still a reason it is not used purely for cancer prevention.
The honest counter-side is mandatory here: finasteride causes sexual adverse effects (erectile dysfunction, decreased libido, ejaculatory problems) in roughly 3-16% of men in trials; a subset report persistent sexual dysfunction that does not resolve after stopping — the contested 'post-finasteride syndrome' — and pharmacovigilance analysis of the WHO VigiBase database found a disproportionality signal for suicidality and psychological adverse events (depression, anxiety), strongest in younger men taking it for hair loss.
These harms are genuinely disputed in magnitude but important enough that they belong front and center. Finasteride is an effective, well-studied prescription drug for hair loss and BPH.
It is not a geroprotector and has no demonstrated lifespan or healthspan benefit; the score reflects strong efficacy for its indications balanced against real and contested side effects.
Competitively inhibits 5α-reductase type II, blocking conversion of testosterone to dihydrotestosterone (DHT).
Reduces serum and scalp/prostate DHT by roughly two-thirds, removing the androgenic driver of follicle miniaturization and prostate growth.
Lower local DHT slows follicle miniaturization (hair) and shrinks prostate tissue — but the same DHT reduction underlies sexual and possibly neurosteroid-mediated effects.
How Finasteride works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Contraindicated — DHT suppression can feminize a male fetus; do not handle broken tablets.
Counsel explicitly on sexual side effects, the disputed persistence risk, and the mood/suicidality signal before starting.
Inform the clinician — PSA is roughly halved and must be interpreted accordingly.
Finasteride lowers PSA by ~50%; the measured value must be doubled or screening thresholds adjusted to avoid masking prostate cancer.
Co-use alters the testosterone-to-DHT ratio; the net androgenic and side-effect profile shifts and should be clinician-managed.
Tip: Reported in ~3-16% of men in trials; usually reversible on stopping, but discuss persistence risk before starting.
Tip: A disputed subset report sexual symptoms that persist after discontinuation; magnitude is contested but counsel patients, especially younger men.
Tip: Pharmacovigilance disproportionality signal (strongest in younger hair-loss users); monitor mood and stop and seek care for depressive symptoms.
Tip: Reversible in most cases; report breast changes to a clinician.
Finasteride has an evidence score of 5.5/10 — moderate evidence based on 319 indexed studies, including 1 meta-analysis. A prescription 5α-reductase type-II inhibitor that lowers DHT to treat male pattern hair loss (1 mg, Propecia) and benign prostatic hyperplasia (5 mg, Proscar). The hair and prostate benefits are well-proven in large RCTs. The honest caveats are real and prominent: sexual side effects (erectile dysfunction, decreased libido) in a minority of men, a disputed but important 'post-finasteride syndrome' with persistent symptoms, and a depression/suicidality safety signal in pharmacovigilance data. It is NOT a longevity drug. Representative study: PMID 38725143.
The commonly studied dose of Finasteride is 1 mg once daily for male pattern hair loss (Propecia); 5 mg once daily for benign prostatic hyperplasia (Proscar). A prescription drug — use under a clinician. Individual needs vary, so check the right dose for you with a healthcare provider.
Timing is flexible for Finasteride — consistent daily use matters more than the time of day. Once daily at a consistent time, with or without food.
Finasteride should be used with caution — talk to a healthcare provider before taking it. Reported side effects include persistent sexual symptoms, depression / anxiety / suicidality signal, decreased libido / erectile dysfunction / ejaculatory problems. How often they occur is not established for all of them. Use caution if any of these apply to you: Women who are or may become pregnant (handling crushed/broken tablets risks feminization of a male fetus); Children / adolescents; Known hypersensitivity to finasteride.
Dutasteride
Too few graded studiesA dual 5α-reductase (type I + II) inhibitor approved for benign prostatic hyperplasia and used off-label for male pattern hair loss. It suppresses DHT more deeply than finasteride (which blocks only type II), and at 2.5 mg (five times the approved dose) it beat finasteride for hair count in one 24-week trial. It carries the same sexual and mood side-effect concerns as finasteride — with a much longer half-life, so any persistent effects clear more slowly. A prescription drug, not a supplement, and not a longevity drug.
Finasteride (topical)
Too few graded studiesThe same drug as oral finasteride, applied to the scalp — with a systemic-sparing claim that the pharmacokinetic data only partly supports.
Minoxidil (oral & topical)
Too few graded studiesA potassium-channel-opening vasodilator — originally an oral antihypertensive — whose well-documented hypertrichosis side effect made it the first FDA-approved hair-loss drug. Topical 2–5% (Rogaine) is OTC and proven in androgenetic alopecia; low-dose ORAL minoxidil (LDOM, ~0.25–5 mg) is an off-label, rapidly adopted alternative with real but generally mild cardiovascular/hypertrichosis side effects. A drug, not a supplement — and not a longevity compound.
Beta-Sitosterol
Too few graded studiesPlant sterol that improved BPH urinary symptoms and urine flow in placebo-controlled trials at 60 to 130 mg a day, without shrinking the prostate. Gram doses of plant sterols for cholesterol are a separate entry.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 320 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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