Finasteride
5-Alpha Reductase Inhibitor | DHT Blocker for Hair Loss & BPH
Community Research
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Finasteride is an FDA-approved 5-alpha reductase inhibitor that blocks the conversion of testosterone to dihydrotestosterone (DHT), the primary androgen responsible for androgenetic alopecia (male pattern hair loss) and benign prostatic hyperplasia (BPH). At 1mg daily, it reduces scalp DHT levels by approximately 66%, slowing or halting hair loss in roughly 90% of men and producing visible regrowth in about 48% over one to two years. Originally developed for prostate enlargement at 5mg (Proscar), the lower 1mg dose (Propecia) was approved specifically for hair loss in 1997. It remains one of only two FDA-approved oral treatments for androgenetic alopecia and has decades of long-term safety data.
Finasteride competitively and selectively inhibits the Type II isoform of the enzyme 5-alpha reductase, which is predominantly found in hair follicles, the prostate, and the liver. This enzyme converts testosterone into dihydrotestosterone (DHT). By blocking this conversion, finasteride reduces serum DHT levels by approximately 70% and scalp DHT by roughly 66% at the 1mg dose. Since DHT is the primary androgen driving miniaturization of hair follicles in genetically susceptible individuals, lowering DHT levels allows affected follicles to recover, extend the anagen (growth) phase, and produce thicker terminal hairs. Notably, finasteride does not block androgen receptors and has minimal effect on testosterone levels, which may increase slightly (by about 10-15%) as a compensatory response to reduced DHT.
Molecular Data
Research Indications
FDA-approved at 1mg daily for the treatment of male pattern hair loss. Demonstrated to halt progression and promote regrowth, particularly at the vertex and mid-scalp regions.
Strongest clinical evidence for regrowth in the vertex region, with significant increases in hair count documented in pivotal clinical trials.
Effective at slowing frontal hairline recession and maintaining mid-scalp density, though regrowth tends to be less dramatic than at the vertex.
Most effective when started early in the hair loss process, before significant miniaturization has occurred. Preservation of existing hair is more reliable than regrowth of lost hair.
FDA-approved at 5mg daily (Proscar) for the treatment of symptomatic BPH. Reduces prostate volume and improves urinary flow over 6-12 months of treatment.
Consistently reduces prostate volume by approximately 20-30% with long-term use, alleviating obstructive urinary symptoms.
Dosing Protocols
Finasteride is administered exclusively as an oral tablet. The 1mg dose (brand name Propecia) is indicated for androgenetic alopecia, while the 5mg dose (brand name Proscar) is indicated for BPH. Tablets should be taken at the same time each day, with or without food. Consistent daily dosing is essential, as DHT levels begin to recover within days of discontinuation.
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Hair loss treatment (standard) | 1mg | Once daily | Oral tablet |
| Hair loss treatment (cost-saving protocol) | 1.25mg (quarter of 5mg Proscar tablet) | Once daily | Oral tablet (quartered) |
| Hair loss treatment (reduced frequency) | 1mg | 3x per week (Mon/Wed/Fri) | Oral tablet |
| Benign Prostatic Hyperplasia | 5mg | Once daily | Oral tablet |
Interactions
What to Expect
Side Effects & Safety
Common Side Effects
- Decreased libido (reported in 1.8% of men in clinical trials vs 1.3% placebo)
- Erectile dysfunction (reported in 1.3% vs 0.7% placebo)
- Decreased ejaculate volume (reported in 0.8% vs 0.4% placebo)
Stop Signs - Discontinue if:
- Persistent sexual dysfunction that does not resolve after dose reduction or discontinuation
- Breast lumps, pain, or nipple discharge (evaluate for gynecomastia)
- Significant mood changes, depression, or suicidal ideation
- Signs of allergic reaction (swelling of lips, tongue, throat, or face)
- Testicular pain that is persistent or worsening
Contraindications
- Women who are pregnant or may become pregnant (finasteride is teratogenic and can cause abnormalities of external genitalia in a male fetus; even handling crushed tablets poses a risk)
- Women who are breastfeeding
- Known hypersensitivity to finasteride or any component of the formulation
- Severe hepatic impairment (finasteride is metabolized by the liver)
- Pediatric patients (not indicated for use in children)
Quality Checklist
Good Signs
- Manufactured by a reputable pharmaceutical company or licensed generic manufacturer
- Tablets are uniform in color and size with clear imprint markings
- Packaging includes lot number, expiration date, and NDC code
- Prescribed through a licensed healthcare provider or legitimate telemedicine platform
- Stored at controlled room temperature in original packaging
Warning Signs
- Tablets obtained from overseas pharmacies without prescription verification
- Compounded formulations without certificate of analysis
- Unusually low pricing that may indicate counterfeit product
- Tablets that crumble easily or have inconsistent coloration
Bad Signs
- No manufacturer information or lot/batch numbers on packaging
- Purchased from unregulated online sources with no pharmacy license
- Tablets with unusual odor, discoloration, or visible defects
- Product that arrives without proper sealed packaging or labeling
References
- Long-term (5-year) multinational experience with finasteride 1 mg in the treatment of men with androgenetic alopeciaKaufman KD, Olsen EA, Whiting D, Savin R, DeVillez R, Bergfeld W, Price VH, Van Neste D, Roberts JL, Hordinsky M, Shapiro J, Binkowitz B, Gormley GJEuropean Journal of Dermatology (1998)
In a 5-year study of 1,553 men, finasteride 1mg daily significantly increased hair count and improved hair appearance. At 5 years, treated men maintained a net increase in hair count compared to a progressive decline in the placebo group. The drug was well tolerated with a low incidence of sexual side effects.
- The effects of finasteride on scalp skin and serum androgen levels in men with androgenetic alopeciaDrake L, Hordinsky M, Fiedler V, Swinehart J, Unger WP, Cotterill PC, Thiboutot DM, Lowe N, Jacobson C, Whiting D, Stieglitz S, Savin R, Clemmensen OJ, Therkildsen P, Lange Brock N, Tun P, Stegink AJ, Waldstreicher JJournal of the American Academy of Dermatology (1999)
Finasteride 1mg reduced scalp skin DHT levels by 64.1% and serum DHT by 68.6%, while serum testosterone increased 9.1%. Demonstrated that oral finasteride significantly reduces DHT both systemically and at the follicular level, providing the mechanistic basis for its efficacy in androgenetic alopecia.
- A randomized, placebo-controlled trial of finasteride for the treatment of androgenetic alopecia in menLeyden J, Dunlap F, Miller B, Winters P, Lebwohl M, Hecker D, Kraus S, Baldwin H, Shalita A, Draelos Z, Markou M, Thiboutot D, Rapaport M, Kang S, Kelly T, Pariser D, Webster G, Hordinsky M, Sperling L, Moy R, Shupack J, Stegink AJ, Waldstreicher JJournal of the American Academy of Dermatology (1999)
In this pivotal Phase III trial, finasteride 1mg daily significantly increased hair count in men with androgenetic alopecia. At 12 months, finasteride-treated patients showed a mean increase of 107 hairs in a 1-inch diameter circle versus a decrease of 50 hairs in the placebo group. Clinical improvements in hair growth were rated favorably by investigators and patients.
- Finasteride in the treatment of men with androgenetic alopeciaMcClellan KJ, Markham ADrugs (1999)
Comprehensive review establishing finasteride 1mg as a well-tolerated and effective first-line treatment for male androgenetic alopecia. Confirmed that finasteride produces clinically meaningful increases in hair count and scalp coverage, with drug-related adverse effects occurring at similar rates to placebo in the majority of patients.
- The importance of dual 5alpha-reductase inhibition in the treatment of male pattern hair loss: results of a randomized placebo-controlled study of dutasteride versus finasterideOlsen EA, Hordinsky M, Whiting D, Stough D, Hobbs S, Ellis ML, Wilson T, Rittmaster RSJournal of the American Academy of Dermatology (2006)
Head-to-head comparison of dutasteride 0.5mg versus finasteride 1mg showed dutasteride produced superior hair counts at 12 and 24 weeks, attributed to dual 5-alpha reductase inhibition. Both agents were well tolerated. Study provides context for finasteride's efficacy as a selective Type II inhibitor and its position relative to dual inhibitors.
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Disclaimer
This information is for educational and research purposes only. Consult a healthcare professional before use.