Finasteride for Men's Hair Loss: What 5 Years of Trials Show and the Side Effects on the FDA Label
Finasteride 1 mg slowed hair loss and regrew hair in placebo-controlled trials lasting up to 5 years. Sexual side effects were uncommon in those trials, but the FDA label now lists persistent sexual problems, depression and suicidal thoughts from post-marketing reports.
By Kymata Health Editorial Published Last checked
This guide
Men's Hair Loss- Question
- Does finasteride work for male pattern hair loss, and how safe is it?
- Sources
- 5 cited
- Quick answers
- 3 questions
- Clinician review
- None; sources cited inline
Key takeaways
5 points- In two 1-year trials of 1,553 men, finasteride 1 mg gave 107 more hairs than placebo in a 5.1 cm² area at 1 year and 138 more at 2 years1.
- At 5 years, 35% of men on finasteride had lost hair from baseline vs 100% of the small placebo group still enrolled2.
- In 1-year trials, 3.8% of men on finasteride reported a sexual side effect vs 2.1% on placebo2.
- The label lists sexual dysfunction that continued after stopping, depression and suicidal ideation from post-marketing reports2.
- There is no FDA-approved topical finasteride; FDA counted 32 adverse-event reports for compounded topical versions from 2019 to 20243.
How it works and what it is approved for
Finasteride blocks type II 5-alpha-reductase, cutting conversion of testosterone to DHT; a 1 mg dose lowers serum DHT by about 65% within 24 hours2. Propecia (finasteride 1 mg) was approved on Dec. 19, 19973, for male pattern hair loss in men only2.
It takes time: the label says daily use for 3 months or more is generally needed before benefit is seen, and stopping reverses the effect within 12 months2.
What the trials show
In two 1-year trials of 1,553 men aged 18 to 41 with vertex hair loss, finasteride improved hair by every measure used, while placebo users kept losing hair1; the trials were led by researchers at Merck, Propecia's original maker1. Extensions ran to 5 years, though the placebo group shrank to 15 men by then2:
- Hair count difference vs placebo: 107 hairs at 1 year, 138 at 2 years and 277 at 5 years, in a 1-inch circle of balding scalp2.
- Further hair loss at 5 years: 35% of men on finasteride vs 100% on placebo2.
- Blinded photo ratings at 5 years: 48% of men on finasteride had more hair and 42% no visible change, vs 6% and 19% on placebo2.
- Relative to other drugs, a 2022 network meta-analysis found 1 mg finasteride produced the largest gain in terminal hair count at 48 weeks among the regimens compared4.
Side effects on the FDA label
In 1-year trials (945 men on finasteride, 934 on placebo), decreased libido affected 1.8% vs 1.3%, erectile dysfunction 1.3% vs 0.7% and ejaculation disorder 1.2% vs 0.7%2. Overall, 3.8% of men on finasteride reported one or more of these vs 2.1% on placebo2. They resolved in men who stopped and in most who continued, and fell to 0.3% or less by year 52. A self-completed sexual-function questionnaire found statistically significant differences favoring placebo in 3 of 4 areas at 12 months2.
Post-marketing reports, which cannot establish frequency or prove cause, add sexual dysfunction that continued after stopping, male infertility or poor semen quality, testicular pain, breast tenderness and enlargement, male breast cancer, depression, and suicidal ideation and behavior2. Persistent sexual, mental and physical symptoms after stopping are sometimes called post-finasteride syndrome; a 2020 review concluded that studies so far can neither confirm nor rule it out as a distinct condition, and that if it exists it seems to affect susceptible people5.
Finasteride lowers PSA, from 0.7 to 0.5 ng/mL on average at 12 months in men 18 to 41, so tell anyone checking your PSA that you take it2. The label also warns that 5-alpha-reductase inhibitors may increase the risk of high-grade prostate cancer: in the 7-year Prostate Cancer Prevention Trial, men 55 and older taking finasteride 5 mg (5 times the hair-loss dose) had more Gleason 8-10 cancers (1.8% vs 1.1%), and a 4-year trial of dutasteride, a related drug, found 1% vs 0.5%2. The label says it has not been established whether this reflects the drugs' effect on prostate size or study-related factors2.
Topical finasteride sprays
Online clinics sell compounded finasteride sprays and finasteride-minoxidil mixes. FDA says there is no FDA-approved topical finasteride, that compounded versions are not evaluated for safety, effectiveness or quality, and that absorption into the bloodstream is expected3.
FDA received 32 adverse-event reports for compounded topical finasteride from 2019 to 2024, describing problems such as erectile dysfunction, anxiety, depression and suicidal ideation, most of which persisted after stopping; some users said prescribers told them a topical form carried no risk3. Uncoated topical products also raise the chance of transfer to others3.
Who should not take it, and what to watch for
Finasteride is contraindicated in women who are or may become pregnant, because it can cause genital abnormalities in a male fetus; women who are or may be pregnant should not handle crushed or broken tablets2. It is not for children2.
Men with a history of depression, sexual dysfunction or infertility should weigh it carefully with the prescriber5; the label lists depression, suicidal ideation and infertility among post-marketing reports and advises caution with liver function abnormalities2. Tell your prescriber promptly about mood changes, and get help right away for thoughts of self-harm (in the US, call or text 988). The label asks men to report breast lumps, pain or nipple discharge promptly2.
Quick answers
Questions
3 answersDo finasteride side effects go away if I stop?
In the trials, they resolved in men who stopped2, but post-marketing reports describe sexual dysfunction that continued after stopping2.
Is topical finasteride safer than the pill?
Not proven. No topical finasteride is FDA-approved, and FDA has adverse-event reports matching those of the pill3.
How long until finasteride works?
Usually 3 months or more of daily use, and the benefit reverses within 12 months of stopping2.
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References
Every study and document cited in this guide, numbered as in the text.
Sources
5 sources- 1Finasteride in the treatment of men with androgenetic alopecia. Finasteride Male Pattern Hair Loss Study Group. J Am Acad Dermatol, 1998. PMID 9777765
- 2PROPECIA (finasteride) tablets: prescribing information (revised 07/2022). U.S. Food and Drug Administration, 2022.
- 3FDA alerts health care providers, compounders and consumers of potential risks associated with compounded topical finasteride products. U.S. Food and Drug Administration, 2025.
- 4Relative Efficacy of Minoxidil and the 5-α Reductase Inhibitors in Androgenetic Alopecia Treatment of Male Patients: A Network Meta-analysis. JAMA Dermatol, 2022. PMID 35107565
- 5Post-finasteride syndrome. An Bras Dermatol, 2020. PMID 32317131
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