Finasteride

Mechanism

Finasteride reduces the conversion of testosterone to dihydrotestosterone, or DHT. It is a nonpeptide small-molecule drug. Lowering DHT can slow hair loss and reduce an enlarged prostate, but those uses involve different products and trials.^307,308

Product formulations

Propecia is the 1 mg oral hair-loss product. Proscar is the 5 mg oral prostate-treatment product. The label strengths have product-specific treatment instructions. A spray containing finasteride and minoxidil is a different formulation again.^307,308,309

Hair-loss trial results

Hair retention and hair growth are distinct trial outcomes.

107 hairs

In the two vertex-baldness trials described in the Propecia label, the one-year difference was 107 hairs in a 5.1 cm² target area: 679 men receiving finasteride were compared with 672 receiving placebo. The 107 is the gap between groups inside that one target area.³⁰⁷

Photograph ratings

At one year, a blinded panel judged hair growth to have increased in 48% of finasteride recipients and 7% of placebo recipients. These photograph ratings are not the same measure as hair counts or a guarantee of visible regrowth for an individual.³⁰⁷

Time and stopping

The label says benefit generally takes at least three months to appear. It also describes reversal of treatment effects within 12 months of stopping. Longer follow-up supports continued benefit, but the extension groups became much smaller and more selected over time.³⁰⁷

Does a spray stay on the scalp?

Topical finasteride can enter the bloodstream, with exposure tied to the studied formulation and amount.

Country approval status

Some finasteride skin sprays were included in the EU safety review. No topical finasteride product is FDA-approved in the United States. Approval of an oral tablet does not approve a spray made from the same ingredient.^310,309

Safety-review findings

The EU review did not establish a causal link between the assessed skin sprays and suicidal thoughts that required new product warnings. FDA separately warned about adverse-event reports involving compounded topical products.^312,309

Two trials of skin sprays

Both trials found a hair-count benefit over placebo. Their products, study populations and measurement areas differed.

European trial

At 24 weeks, the European spray trial reported an adjusted increase of 20.2 target-area hairs with topical finasteride and 6.7 with placebo. It randomized 458 men, but only 250 had usable baseline and follow-up hair-count photographs for its main efficacy population. The oral group gave a comparison; numerical similarity did not prove that the two routes were interchangeable.³¹⁶

Chinese trial

A separate phase III trial at 16 Chinese sites randomized 270 men to a 0.25% spray or placebo; 251 completed 24 weeks. The adjusted hair-count increases were 11.96 and 6.68 in a 0.903 cm² area. The difference was 5.28 hairs, with a 95% confidence interval of 0.98 to 9.59.³¹⁷

Remaining questions

The Chinese trial reported no serious adverse events and no significant difference on its erectile-function questionnaire. That does not establish a zero risk. The manufacturer supplied the study products and supported the trial; longer follow-up and rare-event risks remain separate questions.³¹⁷

Mood changes deserve a clear answer

Regulatory records distinguish suicidal thoughts, depression and completed suicide.

Recognised risk, unknown frequency

The EU review confirmed suicidal thoughts as a side effect of oral 1 mg and 5 mg finasteride. It could not estimate how often this happens. This conclusion is stronger than saying reports alone cannot prove causation, and narrower than claiming a known increase in completed suicides.^310,312

The current UK advice

For the 1 mg hair-loss tablet, the MHRA advises stopping treatment and contacting a healthcare professional if depression or suicidal thoughts develop. For the 5 mg prostate tablet, it advises contacting a clinician promptly. Its 2026 update also calls for discussion of mental-health history and monitoring during treatment.³¹¹

Where regulators disagreed

The final EU decision kept approved uses available with added safety measures. French and Belgian representatives disagreed about the benefit-risk balance of the 1 mg hair-loss tablet. Their dissent is part of the record; it was not an EU ban.^310,313

Sexual symptoms and persistence

Trial results during treatment do not tell us the chance of symptoms continuing after treatment.

3.8% vs 2.1%

One or more of the listed sexual adverse experiences were reported by 36 of 945 men receiving oral 1 mg finasteride and 20 of 934 receiving placebo. The label reports these as 3.8% and 2.1%. These trial proportions cover the treatment period only.³⁰⁷

After stopping

The label includes spontaneous reports of sexual dysfunction continuing after discontinuation; those reports cannot give the frequency of persistence or its duration for one person. Both the controlled-trial findings and the postmarketing warning belong in the discussion.^307,311

Fertility

Reduced ejaculate volume is not the same as infertility. Poor semen quality and infertility have been reported, with improvement after stopping in some reports.^307,308

Why safety studies can disagree

The studies used distinct populations, doses, follow-up periods and outcome definitions.

Limits of the hair-loss trials

A 2015 review assessed safety reporting in 34 finasteride hair-loss trials. None met its definition of adequate reporting, and 26 followed safety for a year or less. That finding identifies a weakness in the evidence; it does not tell us how often a particular harm occurs.³¹⁸

A large 2026 follow-up found no signal

A newer PCPT study linked participants to Medicare records. Among 14,239 men with usable coverage, followed for a median of 20 years from enrolment, none of 22 claims-defined conditions was significantly associated with the earlier finasteride assignment. This is relevant evidence from older men assigned oral 5 mg. It does not directly answer every question about persistent symptoms in younger hair-loss users.³¹⁹

Prostate studies

Prostate studies in older men address prostate outcomes rather than hair loss.

Progression and surgery

In the four-year PLESS study of 3,040 men with symptomatic BPH, the label reports acute urinary retention or BPH-related surgery in 6.6% of the oral 5 mg group and 13.2% of the placebo group. This outcome concerns prostate disease, not hair growth.³⁰⁸

The cancer warning remains

The March 2026 Proscar label retains the PCPT warning: Gleason 8-10 prostate cancers occurred in 1.8% of men receiving oral 5 mg finasteride and 1.1% receiving placebo. The trial enrolled men aged 55 and over. This finding should not be recast as proof that a young hair-loss user has the same risk.³⁰⁸

Longer follow-up adds context

The PCPT survival follow-up found no significant difference in overall survival after up to 18 years. Fewer prostate cancers were diagnosed in the finasteride group, while the earlier high-grade finding remained part of the record. The result does not establish a survival benefit and does not remove the current label warning.³²⁰

Who the evidence covers

Approved indications remain specific to their product and population.

Women and pregnancy

Propecia is indicated for men. In a 12-month trial of 137 postmenopausal women, oral 1 mg finasteride did not demonstrate hair-loss benefit. Finasteride also carries pregnancy precautions because it can harm development of a male fetus; the labels warn against handling crushed or broken tablets during pregnancy or when pregnancy is possible.^307,308

Compounding and quality

FDA approval, lawful compounding and product quality are different questions. A compounded preparation is not FDA-approved. FDA recall records also show that formulation and labelling failures can occur, including cross-contamination of compounded finasteride capsules with another active drug.^309,314,315

Common questions

Hair growth, side effects, topical products and what happens after stopping.

01 Why are Propecia 1 mg and Proscar 5 mg different?

Propecia is the US 1 mg oral product indicated for male pattern hair loss in men; Proscar is the US 5 mg oral product for symptomatic benign prostatic hyperplasia and related BPH outcomes. Sharing finasteride as the active ingredient does not make the products, indications, or evidence interchangeable. These records do not support turning the 5 mg BPH product into a hair-loss instruction.^307,308

02 How well does finasteride work, and what does 107 hairs mean?

Two one-year trials randomized 1,553 men aged 18 to 41. In the vertex analysis, the baseline mean was 876 hairs in a 5.1 cm² circle and the 12-month between-group difference was 107 hairs, with 679 finasteride and 672 placebo participants analyzed. The 107 is the gap between the groups inside that defined area. Trial averages cannot guarantee an individual's result.^321,307

03 How long does it take to work?

The Propecia label says benefit generally takes at least three months, and the pivotal program showed clear group separation by six months. The checked sources do not define a required initial shedding phase or prove that worsening means treatment is working. Apparent worsening or a pattern outside the studied indication needs assessment for other causes of hair loss rather than being assigned to a universal timeline.^307,321

04 What happens if I stop?

The label says continued use is needed to sustain benefit and that withdrawal reverses the effect within 12 months. In the extension, men switched from finasteride to placebo lost their hair-count increase during the following year. Those are group observations and do not give an exact personal reversal date.^307,321

05 Does it work for a receding hairline or every kind of hair loss?

Evidence is strongest for mild to moderate vertex and anterior mid-scalp androgenetic alopecia in men. Propecia’s label says bitemporal-recession efficacy is unestablished, and the anterior mid-scalp count excluded the frontal hairline and bitemporal areas. Other patterns and causes of hair loss were not established as finasteride indications by these records.^307,321

06 How common were sexual side effects in trials?

In year one of controlled hair-loss trials, decreased libido was 1.8% versus 1.3%, erectile dysfunction 1.3% versus 0.7%, and ejaculation disorder 1.2% versus 0.7%; at least one was reported by 3.8% versus 2.1%. A meta-analysis of 15 androgenetic-alopecia trials found a higher relative risk of sexual dysfunction with 5-alpha-reductase inhibitors, while a separate review found adverse-event reporting quality inadequate in every included finasteride trial. Trial percentages describe their populations and follow-up, not a personal risk prediction.^307,322,318

07 Can side effects last after stopping?

The Propecia label and current UK warning list reports of sexual dysfunction continuing after discontinuation, but voluntary reports cannot estimate how often this occurs. A 2026 Medicare analysis of 14,239 older PCPT participants previously assigned 5 mg found no significant association across 22 claims-defined conditions over a median 20 years, yet that population and endpoint set do not settle persistent symptoms in younger 1 mg hair-loss users. Persistent symptoms deserve clinical evaluation; the records do not yield a personal probability.^307,311,319

08 What do regulators say about depression and suicidal thoughts?

EMA’s 2025 EU review confirmed suicidal ideation as a side effect of oral 1 mg and 5 mg finasteride, with unknown frequency, and EU and UK risk measures were updated. EMA found insufficient evidence for a causal association with completed suicide and found no evidence linking suicidal ideation to the evaluated finasteride skin sprays. The spray finding applies only to the evaluated products. EMA concluded that benefits still outweigh risks for approved uses, while mood changes or suicidal thoughts warrant prompt medical contact.^{310,312,311,323}

09 Can finasteride affect fertility or pregnancy plans?

One placebo-controlled 1 mg study in 181 young men, with semen data in a 79-person subset, found no significant effect on sperm concentration, total sperm per ejaculate, motility, or morphology over 48 weeks. A separate 5-alpha-reductase inhibitor study found mild semen-parameter decreases that generally appeared reversible, and the current labels also list postmarketing infertility or poor seminal quality. Pregnancy handling is separate: people who are or may be pregnant should not handle crushed or broken tablets, while the intact coating prevents normal contact with the active ingredient.^{324,325,307,308}

10 Is topical finasteride effective, safer, or FDA approved?

Two specific topical spray trials showed 24-week target-area hair-count benefits versus placebo: the European trial randomized 458 men but only 250 had usable baseline and on-treatment hair counts, and the Chinese trial randomized 270 men with a 5.28-hair difference in 0.903 cm². The European spray had lower systemic exposure than oral finasteride but still reduced serum DHT, and numerical similarity to oral finasteride did not establish interchangeability or noninferiority. FDA says no topical finasteride product is US approved and compounded versions lack premarket review, so these product-specific short trials do not establish that every topical preparation is safer or equivalent.^{316,317,326,309}

11 How does it compare with dutasteride?

A 24-week trial in 917 men found dutasteride 0.5 mg superior to finasteride 1 mg on target-area hair count, hair width, and frontal photographic assessment. The short trial did not establish long-term comparative durability or uncommon-harm rates.³²⁷

12 How does it compare with minoxidil or the combination?

A 12-month randomized comparison enrolled 450 Chinese men and evaluated 428; categorical improvement was reported in 80.5% with oral finasteride, 59.0% with topical minoxidil, and 94.1% with the combination. The combination ranked highest on that study’s outcome. Its endpoint, population, blinding, route, and tolerability differ from the pivotal vertex hair-count trials, so the percentages are not interchangeable with the 107-hair result.^328,321

13 Can women use finasteride, and what is the pregnancy warning?

US Propecia is not indicated in women or pediatric patients, and a 12-month randomized 1 mg study in 137 postmenopausal women did not show benefit. That null result applies to that population and does not answer every off-label population or formulation. People who are or may be pregnant should not handle crushed or broken tablets because exposure can harm development of external genitalia in a male fetus; intact tablets are coated for normal handling.^307,329

14 How does it affect PSA and prostate-cancer screening?

Finasteride lowers PSA. In the 1 mg Propecia trials, mean PSA fell from 0.7 to 0.5 ng/mL at 12 months; the 5 mg Proscar label says PSA falls about 50% within six months, advises establishing a new baseline, and says isolated values after six months should be doubled for comparison with untreated men. The original PCPT found fewer total prostate cancers but more high-grade diagnoses in older men assigned 5 mg, while 18-year follow-up found no survival difference; these records do not quantify that issue for younger 1 mg hair-loss users.^{307,308,330,320}

15 What interactions or monitoring issues matter?

The checked labels found no clinically important interactions in the studied set and finasteride did not appear to affect CYP-linked metabolism, but that is not proof of no interaction in every combination. Liver abnormalities warrant caution because finasteride is extensively metabolized in the liver, and PSA interpretation must be adjusted. A prescriber needs the exact product, indication, other medicines, liver history, fertility plans, mood or sexual symptoms, and PSA context.^307,308