Finasteride: Uses, Side Effects, Dosage, and Results (2026 Guide)

Finasteride is a prescription-only 5-alpha-reductase inhibitor (5ARI). The FDA approved finasteride 5 mg (brand name Proscar) in 1992 for benign prostatic hyperplasia (BPH) and finasteride 1 mg (Propecia) in 1997 for male pattern hair loss (androgenetic alopecia, AGA). It works by blocking the Type II isoenzyme of 5-alpha-reductase, the enzyme that converts testosterone into dihydrotestosterone (DHT), reducing serum DHT by approximately 70% and scalp DHT by roughly 64%. The standard dose for hair loss is 1 mg once daily; for BPH, 5 mg once daily. Generic finasteride in both strengths is widely available. This page is medically reviewed and covers how finasteride works, its clinical evidence, dosage, side effects, cost, and comparison with minoxidil.

What Is Finasteride?

Finasteride is the generic name for a synthetic 4-azasteroid compound developed by Merck & Co. It belongs to the pharmacological class of 5-alpha-reductase inhibitors (5ARIs) and is available in the United States only by prescription. The molecule was first approved by the FDA in 1992 as Proscar (5 mg) for BPH, and in 1997 as Propecia (1 mg) for male androgenetic alopecia — making it the first and, as of 2026, the only FDA-approved oral treatment for male pattern hair loss.

Finasteride selectively and competitively inhibits the Type II isoenzyme of 5-alpha-reductase, which is the predominant isoenzyme in the scalp, prostate, seminal vesicles, and epididymis. A related drug, dutasteride (Avodart), inhibits both Type I and Type II isoenzymes and is FDA-approved for BPH, but is not approved for hair loss in the United States (though approved for AGA in South Korea and Japan).

Two FDA-approved finasteride formulations exist: Propecia (1 mg) for male pattern hair loss and Proscar (5 mg) for BPH. Generic versions of both strengths are widely available and substantially less expensive than the original brand names.

Read the complete encyclopedic guide: What Is Finasteride?

How Finasteride Works

Finasteride’s mechanism centers on the dihydrotestosterone (DHT) pathway. DHT is a potent androgen approximately five times more biologically active than testosterone. It is synthesized from testosterone by the enzyme 5-alpha-reductase, primarily the Type II isoenzyme in the scalp and prostate.

In men genetically predisposed to androgenetic alopecia (AGA), DHT binds to androgen receptors in susceptible scalp follicles, progressively shortening the anagen (growth) phase and shrinking the follicle in a process called miniaturization. Finasteride interrupts this cycle by inhibiting the Type II enzyme, reducing serum DHT by approximately 70% and scalp DHT by roughly 64% (Kaufman et al., 1998; Dallob et al., 1994).

In the prostate, elevated DHT is the primary driver of glandular growth. Reducing DHT with finasteride shrinks prostate volume by approximately 20–30% over 6–12 months of treatment, improving urinary flow and reducing the risk of acute urinary retention in men with BPH.

Testosterone levels are not meaningfully reduced by finasteride — only the conversion of testosterone to DHT is blocked. The drug does not affect the testosterone-to-estradiol conversion pathway.

Detailed mechanism: 5-alpha-reductase, DHT, and finasteride pharmacology

Finasteride for Hair Loss (Propecia 1 mg)

Finasteride 1 mg (Propecia) is the only FDA-approved oral medication for male androgenetic alopecia. AGA affects approximately 50% of men by age 50 and is characterized by a predictable pattern of frontal hairline recession and vertex thinning driven primarily by DHT acting on genetically sensitive follicles.

Evidence from the pivotal 1-year and 5-year double-blind, placebo-controlled trials (Kaufman et al., 1998; Kaufman et al., 1999):

• Hair loss was halted or improved in 83–87% of treated men vs. 28% on placebo at 1 year
• Visible regrowth was observed in 48% of men at the vertex and 36% at the anterior mid-scalp (vs. 7% and 16% on placebo)
• Clinical benefit was maintained over 5 years of continuous treatment in the majority of men
• Men who discontinued finasteride returned to pre-treatment hair loss levels within 6–12 months

Finasteride for hair loss is indicated for adult men only. It is not FDA-approved for women, and its use in women who are or may become pregnant is contraindicated due to the risk of fetal urogenital abnormalities in male pregnancies (see Side Effects for teratogenicity details).

Complete guide: Finasteride for male pattern hair loss (AGA)

Finasteride for BPH (Proscar 5 mg)

Finasteride 5 mg (Proscar) is FDA-approved for the treatment of symptomatic benign prostatic hyperplasia (BPH) in adult men. BPH is a non-cancerous enlargement of the prostate gland affecting more than 50% of men over age 60, causing lower urinary tract symptoms such as weak urine stream, frequency, urgency, nocturia, and incomplete bladder emptying.

Results from the 4-year PLESS trial (Proscar Long-term Efficacy and Safety Study; McConnell et al., 1998):

• Prostate volume reduced by approximately 20–30% over 12 months
• Risk of acute urinary retention reduced by 57% vs. placebo over 4 years
• Likelihood of BPH-related surgery reduced by 55% vs. placebo

Finasteride 5 mg is commonly combined with an alpha-1 blocker (e.g., tamsulosin) for men with larger prostates. The MTOPS trial (Medical Therapy of Prostatic Symptoms; McConnell et al., 2003) demonstrated that combination therapy produced superior symptom reduction and reduced the risk of clinical progression compared to either drug alone.

Complete guide: Finasteride for BPH and lower urinary tract symptoms

Finasteride Dosage: 1 mg vs. 5 mg

Two FDA-approved strengths of finasteride exist, each for a specific indication:

Indication	Dose	Brand Name	Generic?	Duration
Male pattern hair loss (AGA)	1 mg once daily	Propecia	Yes	Continuous; benefit lost if stopped
Benign prostatic hyperplasia (BPH)	5 mg once daily	Proscar	Yes	Minimum 6 months to assess response

Both formulations are taken orally, with or without food, at approximately the same time each day. Tablets should be swallowed whole. Pregnant women must not handle crushed or broken tablets due to the risk of skin absorption and fetal harm in male pregnancies; intact tablets have a protective coating.

If a dose is missed, take it as soon as remembered. If it is nearly time for the next dose, skip the missed dose; do not double up. Finasteride is not indicated in pediatric patients.

Complete dosage guide: 1 mg vs. 5 mg, administration, and missed doses

Finasteride Side Effects

Finasteride is generally well tolerated. In clinical trials, sexual side effects — the most commonly reported adverse effects — occurred in a minority of men and were higher than placebo but at low absolute rates:

Side Effect	Finasteride 1 mg	Placebo
Decreased libido	1.8%	1.3%
Erectile dysfunction	1.3%	0.7%
Ejaculation disorder (decreased volume)	0.8%	0.4%
Breast enlargement or tenderness (gynecomastia)	0.4%	0.2%

Persistent side effects (Post-Finasteride Syndrome): In 2012, the FDA updated the finasteride label to note that sexual side effects — including decreased libido, erectile dysfunction, and ejaculatory disorders — may persist after stopping the drug in some men. This is referred to as Post-Finasteride Syndrome (PFS). The frequency and mechanisms of persistent effects remain subjects of ongoing research. Any persistent side effects after stopping finasteride should be discussed with a physician.

PSA effects: Finasteride reduces serum PSA levels by approximately 50% in men with BPH. Clinicians should double a patient’s PSA value obtained while on finasteride when interpreting it for prostate cancer screening purposes.

Teratogenicity (Pregnancy Category X): Finasteride is contraindicated in women who are or may become pregnant. Women should not handle crushed or broken finasteride tablets. The risk is fetal genital abnormalities in male pregnancies due to inhibition of Type II 5-alpha-reductase.

Complete side effects guide | Post-Finasteride Syndrome: what the evidence shows

Finasteride vs. Minoxidil

Finasteride and minoxidil are the two most widely used treatments for male pattern hair loss. They work through entirely different mechanisms and are commonly used in combination:

	Finasteride 1 mg (oral)	Minoxidil 5% (topical)
Mechanism	Reduces DHT synthesis (hormonal)	Vasodilator; extends anagen phase
FDA-approved for male AGA	Yes (1997)	Yes (1988)
Prescription required	Yes	No (OTC)
Hair loss halted at 12 months	~83%	~60–67%
Onset of visible results	3–6 months	4–8 months
Typical side effects	Sexual (rare; 1–2%)	Scalp irritation, initial shedding
Combination benefit	Yes. Complementary mechanisms; combination shown superior to monotherapy (Badri et al., 2021 systematic review)

Both medications require continuous use to maintain benefit; stopping either typically results in resumption of hair loss. Treatment choice depends on patient preference, medical history, tolerance of side effect profiles, and physician guidance.

Full comparison: Finasteride vs. minoxidil for male hair loss

How Long Does Finasteride Take to Work?

Most men using finasteride for hair loss do not see visible results for 3–6 months. This delay reflects the biology of the hair growth cycle: finasteride suppresses DHT within weeks, but visible improvement requires follicles to complete a full anagen cycle and produce thicker, healthier hairs. The timeline below reflects what clinical trials and real-world experience typically show:

• Weeks 2–8 — Initial shedding: A temporary increase in hair shedding (“finasteride shed”) occurs in some men as follicles transition cycles. This is a normal, transient response, not evidence that the drug is failing.
• Months 3–6 — Stabilization: DHT suppression is established; the majority of men notice slowing or stabilization of hair loss.
• Months 6–12 — Visible improvement: For most responsive men, this is the window of most noticeable regrowth and thickening.
• 12–24 months — Peak response: The 1-year and 2-year marks represent peak clinical response in published trials; continued daily use maintains benefit indefinitely.

For BPH, improvements in urinary flow symptoms typically begin within 6 months of starting treatment. Finasteride must be taken continuously to maintain benefit; stopping leads to return of hair loss and prostate regrowth within 6–12 months.

Finasteride results timeline: what to expect at 3, 6, 12, and 24 months

Finasteride Cost and Getting a Prescription

Generic finasteride 1 mg is among the most affordable prescription hair loss treatments available. Estimated monthly costs as of 2026:

Source	Est. monthly cost (2026)	Notes
Generic pharmacy (with GoodRx / discount coupon)	$15–$35	Prices vary by pharmacy; use GoodRx or NeedyMeds to compare
Telehealth platforms (Hims, Keeps, Roman)	$20–$45	Includes online consultation; subscription pricing common
Brand-name Propecia	$70–$100+	Therapeutically identical to generic finasteride 1 mg
Proscar 5 mg (quartered)	~$10–$20	Off-label cost-reduction strategy; only under physician guidance

Finasteride requires a prescription in the United States (Schedule not required; it is not a controlled substance). Prescription options include a primary care physician, dermatologist, urologist, or telehealth platform. Multiple US telehealth services (Hims, Keeps, Roman, Sesame Health) offer online consultations and finasteride prescriptions, often with same-day or next-day delivery.

Finasteride cost guide: insurance, generics, GoodRx, and telehealth pricing

Frequently Asked Questions

Does finasteride work for a receding hairline?

Finasteride is most effective at the vertex (crown) and mid-scalp, where DHT-driven miniaturization is typically most active. Evidence for anterior hairline restoration is more limited; some men see modest improvement over 2+ years of continuous use, but full hairline restoration in cases of significant recession is generally not expected. Finasteride is most effective when started early in the course of hair loss.

Can women take finasteride?

Finasteride is not FDA-approved for use in women and is contraindicated in women who are or may become pregnant (Pregnancy Category X). The drug causes fetal genital abnormalities in male pregnancies. Postmenopausal women with androgenetic alopecia are sometimes prescribed finasteride off-label under close physician supervision, but this is not standard US practice and requires careful consideration of individual risk-benefit factors.

What is Post-Finasteride Syndrome (PFS)?

Post-Finasteride Syndrome (PFS) refers to reported persistent sexual, neurological, and psychological side effects that some men experience after stopping finasteride. The FDA updated the finasteride prescribing information in 2012 to acknowledge that sexual side effects may persist after discontinuation. The condition is recognized clinically, but large, well-controlled epidemiological studies on its frequency and mechanisms remain limited. Men experiencing persistent symptoms after stopping finasteride should consult a physician.

Does finasteride increase prostate cancer risk?

No. In the Prostate Cancer Prevention Trial (PCPT; Thompson et al., 2003), finasteride 5 mg reduced overall prostate cancer incidence by 24.8% over 7 years compared to placebo. The trial also found a higher prevalence of high-grade (Gleason 7–10) prostate cancer in the finasteride arm; subsequent analyses (Lucia et al., 2007; Thompson et al., 2013) indicate this likely reflects a detection artifact due to reduced prostate volume improving biopsy sampling sensitivity, not a true increase in aggressive cancer incidence. Regulatory agencies and major urology guidelines do not conclude that finasteride causes high-grade prostate cancer.

What happens when you stop taking finasteride?

Within 6–12 months of stopping finasteride, DHT returns to pre-treatment levels and hair loss resumes at the rate it would have followed without treatment. Any hair regrowth achieved during treatment is generally lost over this period. There is no evidence of a “rebound” effect that accelerates hair loss beyond the expected baseline trajectory. For BPH, prostate volume begins to return to pre-treatment size after stopping finasteride.

Sources and References

• Kaufman KD, et al. “Finasteride in the treatment of men with androgenetic alopecia.” J Am Acad Dermatol. 1998;39(4):578–589. doi:10.1016/s0190-9622(98)70007-6
• Dallob AL, et al. “The effect of finasteride, a 5 alpha-reductase inhibitor, on scalp skin testosterone and dihydrotestosterone concentrations in patients with male pattern baldness.” J Clin Endocrinol Metab. 1994;79(3):703–706.
• McConnell JD, et al. “The effect of finasteride on the risk of acute urinary retention and the need for surgical treatment among men with benign prostatic hyperplasia.” N Engl J Med. 1998;338(9):557–563. (PLESS Trial)
• McConnell JD, et al. “The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of benign prostatic hyperplasia.” N Engl J Med. 2003;349(25):2387–2398. (MTOPS Trial)
• Thompson IM, et al. “The influence of finasteride on the development of prostate cancer.” N Engl J Med. 2003;349(3):215–224. (PCPT)
• Badri T, Nessel TA, Kumar D. “Minoxidil.” StatPearls. Treasure Island (FL): StatPearls Publishing; 2024.
• Merck & Co. Propecia (finasteride 1 mg) US Prescribing Information. Revised 2022.
• U.S. Food and Drug Administration. Drug Safety Communication: 5-alpha reductase inhibitors (5-ARIs) may increase the risk of a more serious form of prostate cancer. June 9, 2011.