Finasteride and penile shrinkage: what we know

Some men say their penis became smaller or curved while they took finasteride, or after stopping it. As of October 2026, neither the UK leaflet nor the US label lists these changes, though some men with post-finasteride syndrome (PFS) report them.

The evidence is thin: mostly one small clinic study and counts of reports sent to regulators. None of it shows that finasteride was the cause. It’s still a hard thing to raise with a doctor, and the leaflet gives you nothing to point to.

Dr Maria Uloko is a US urologist who specialises in sexual medicine. In 2023 she gave colleagues a talk on sexual problems that medicines can cause, and she began with PFS.

Play video: Common Drug-Induced Sexual Dysfunction in Men

PFS is a controversial diagnosis among urologists, she told them, but not for the patients who have the symptoms. Her list of symptoms, a little later in the talk, included penile shrinkage, next to erection problems and a lower sex drive.

Does finasteride cause penile shrinkage?

Nobody has shown that it does. What exists is men saying it happened to them.

The main study comes from a urology clinic in Houston. Its doctors studied 25 men with lasting symptoms after finasteride, all seen there for sexual problems. Asked about changes to their genitals, 9 of the 25 said they had lost length.

That is the men’s own account. The study reports no measurements, from before finasteride or after. Only these 25 men were asked, so there’s nothing to compare their answers with.

The other numbers are counts of reports. Anyone who suspects a side effect can send one to a medicines regulator.

A 2025 analysis covered twenty years of reports to the US regulator with finasteride as the main suspect. Several hundred described a penis that had got smaller.

A report is one person’s suspicion. More than half of all the finasteride reports in that analysis, of any side effect, came from the public. A count isn’t a rate, and it can’t show that finasteride was the cause.

What each kind of evidence can tell you

1

The leaflet and the label

The official list of side effects. A change in size or shape isn't on it.

2

One clinic study

What 25 men who came for help described. It can't show how often this happens, or why.

3

Reports to regulators

Each is one person's suspicion, put on the record. A count of reports isn't a rate.

Can finasteride cause Peyronie’s disease?

That hasn’t been shown either. Peyronie’s disease makes the penis curve when it’s erect, and reports of it with finasteride have been counted.

Researchers in Italy and the UK searched the US and EU databases for reports of a curved penis or Peyronie’s disease. In the US regulator’s database, 214 named finasteride. That was a bigger share of its reports than for the other medicines they compared.

They called that a strong signal, which means a pattern that needs checking. They also wrote that it can’t confirm a cause, and that the idea “remains highly speculative”.

The doctors and researchers who wrote the 2022 diagnostic criteria for PFS say there’s some evidence of a curve in men with PFS. It isn’t clear, they add, whether it was there before treatment.

The NHS says a slight curve can be natural, and that the cause of Peyronie’s disease isn’t always known. It can follow an injury to the penis, and is more likely with diabetes, high blood pressure or high cholesterol. It lists certain medicines too; finasteride isn’t among its examples.

Play video: What is Erectile Dysfunction?

Is penile shrinkage a symptom of PFS?

Some men with PFS describe it, but the definitions we checked don’t include it. Orphanet, a European database of medical conditions, defines PFS by sexual problems, genital numbness, breast swelling, depression and brain fog, among others. A change in size or shape isn’t on its list.

Patients do bring it up. In 2023, men with PFS spoke to staff at the US medicines regulator. One said he noticed shrinkage within a few weeks of starting finasteride, and another that a curve developed after he stopped. Both accounts are in the patient group’s summary of the session.

Connor took finasteride for six months and later wrote his story for this site. His list of physical effects begins with “genital shrinkage” and numbness.

Numbness comes up in these accounts too: see what PFS feels like and genital numbness and medicines.

What can I do?

Finasteride helps many men keep their hair. If you have side effects, that’s a decision for you and your prescriber.

The NHS says to see a GP if your penis curves when it’s erect, if you find a hard lump, or if erections hurt. That holds whatever the cause. “Do not feel embarrassed about getting help,” the NHS adds: GPs are used to dealing with this.

Give your GP the dates in one line: “Finasteride 1 mg from March 2024, last tablet January 2025. A curve and painful erections, first noticed in November 2024.”

Report it: it helps everyone

A doctor’s note helps you. A report to the medicines regulator helps everyone else: it is how patterns get noticed.

• No proof needed. A suspicion is enough, even years after stopping.
• Where: the Yellow Card scheme in the UK, MedWatch in the US.
• Use the right words. Say plainly what changed. The US database files these reports under penile size reduced and penile curvature. If symptoms continued after stopping, write Post 5-alpha-reductase inhibitor syndrome (MedDRA 10082430).

Our reporting guide walks you through it

What else do people ask?

Does it go away after stopping? Nobody knows. We found no study that has followed men with this change over time. The leaflet’s list of problems that continued after stopping covers erections, sex drive and ejaculation: more in can a medicine cause lasting erection problems? and finasteride’s sexual side effects.

What did the blood-flow scans find? The Houston doctors scanned blood flow in the penis in 24 of the 25 men. In 17, the scan showed something outside the normal range, some of it borderline. Only these men were scanned, and the study reports no scans from before finasteride. With nothing to compare against, the study can’t say what caused the findings.

Has a regulator looked into it? Not that we could find, as of October 2026. The UK regulator’s 2024 safety review of finasteride doesn’t mention shrinkage or a curve. Nor does the EU regulator’s page on its 2025 review.

Dr Uloko’s advice to her colleagues was to take what their patients tell them seriously. If something has changed, tell your GP, and read about post-finasteride syndrome.

Sources

Every source below was opened on 12 October 2026.

1. Propecia 1 mg film-coated tablets, patient information leaflet (UK, electronic Medicines Compendium), Organon, last revised May 2026. Section 4 lists, under “Frequency unknown”, pain in the testicles and persistent difficulty having an erection, persistent decrease in sex drive and persistent problems with ejaculation “after discontinuation of treatment”. The leaflet does not mention the size, length, shape or curvature of the penis, or Peyronie’s disease.
2. Propecia 1 mg, summary of product characteristics (UK), text revised 29 June 2026. Section 4.8 does not list a change in penile size, penile curvature or Peyronie’s disease. The UK leaflet for the 5 mg tablet, Proscar (last revised August 2024), does not mention them either.
3. Propecia, US prescribing information (DailyMed), prescribing information revised August 2022, patient information revised November 2023. Postmarketing experience, reproductive system: “sexual dysfunction that continued after discontinuation of treatment, including erectile dysfunction, libido disorders, ejaculation disorders, and orgasm disorders”, male infertility or poor seminal quality, testicular pain and haematospermia. No mention of penile size, penile curvature or Peyronie’s disease.
4. Khera M, Than JK, Anaissie J and colleagues. Penile vascular abnormalities in young men with persistent side effects after finasteride use for the treatment of androgenic alopecia. Translational Andrology and Urology, 2020; 9(3): 1201–1209. Baylor College of Medicine urology clinic, Houston, March 2013 to September 2018. 25 men being seen for sexual dysfunction after finasteride for hair loss (median age 38), and 28 comparison men. Only the finasteride group was asked about genital complaints, with a non-validated survey, and only that group had a penile Doppler ultrasound. 9 of 25 reported loss of penile length; no measurements are reported. 24 of 25 were scanned; 17 had “some vascular abnormality”: 8 arterial insufficiency, 5 in a “gray zone” of possible erectile dysfunction, 4 venous leak. Limitations named by the authors: uneven survey completion between groups, variable length of treatment, selection bias, no questionnaire data from before treatment, and no scans in the comparison group.
5. Zhong X, Yang Y, Wei S, Liu Y. Multidimensional assessment of adverse events of finasteride: a real-world pharmacovigilance analysis based on FDA Adverse Event Reporting System (FAERS) from 2004 to April 2024. PLoS One, 2025; 20(3): e0309849. More than 11,500 reports in the US Food and Drug Administration’s database (which also receives reports from other countries) with finasteride as the primary suspected drug, first quarter of 2004 to first quarter of 2024. Table 2, by preferred term: “Penile size reduced” 398 reports, “Peyronie’s disease” 215, “Penile curvature” 63. Table 1: 53.67% of all these finasteride reports, whatever side effect they described, came from consumers; the paper gives no reporter breakdown for the penile reports alone. These are counts of reports, not rates, and not proof of cause. The authors note the reports may be incomplete or inaccurate and that the analysis could not account for other explanations.
6. Schifano N, Capogrosso P, Boeri L and colleagues. Are finasteride-related penile curvature/Peyronie’s disease adverse event reports worthy of further clinical investigation? International Journal of Impotence Research, 2023; 35(5): 465–471. Read as an abstract only; the full text is behind a paywall. The abstract does not give the years covered. It counts 860 reports of “penile curvature” and/or “Peyronie’s disease” in the US database, 214 of them associated with finasteride, and compares finasteride with the nine other medicines most often named. Proportional reporting ratio 6.6 in the US database and 11.8 in the EU one, described as “strong signals of disproportionality”. Most reports (56.9%) were submitted by healthcare professionals. For 97 of the 214, the report was not part of a cluster suggesting PFS. The authors: the findings are “not useful to confirm any causal association”, and the hypothesis “remains highly speculative due to the very questionable quality of present data”.
7. Healy D, Bahrick A, Bak M and colleagues. Diagnostic criteria for enduring sexual dysfunction after treatment with antidepressants, finasteride and isotretinoin. International Journal of Risk & Safety in Medicine, 2022; 33(1): 65–76. Section 5: “There is some evidence for penile curvature or other penile effects in men with PFS, but it is not clear if this was present prior to treatment or has resulted since.” Its reference for that line is the Khera study above. The paper’s criteria for PFS do not list a change in penile size or shape.
8. Orphanet, Post 5-alpha-reductase inhibitors treatment syndrome, ORPHA:686468, its entry for the condition known as post-finasteride syndrome. The definition lists impaired sexual function, genital numbness or paraesthesia, gynaecomastia, depression, brain fog and anxiety, with muscle, joint, fatigue, migraine, body temperature and skin symptoms as additional ones. It does not list a change in penile size or shape.
9. PFS Network, FDA Patient Listening Session on Post-Finasteride Syndrome, 2 June 2023. The summary was written by PFS Network, the patient group that hosted the session, and is published on the US Food and Drug Administration’s website. Patient 5 noticed “penile shrinkage” within a few weeks of being given finasteride. Patient 4 developed “penile curvature” among the symptoms that followed discontinuation.
10. NHS, Peyronie’s disease, page last reviewed 3 June 2024. It mainly affects men over 40, but younger men can also get it. The cause is not always known; it can sometimes follow an injury to the penis; it is more likely with diabetes, high blood pressure, high cholesterol, coronary heart disease, and with certain medicines, “such as beta blockers or antidepressants”. See a GP for swelling or a hard lump, a penis that curves when erect, or painful erections. “Do not feel embarrassed about getting help.”
11. MHRA, Safety review of finasteride: public assessment report, April 2024. The report does not mention penile shrinkage, penile curvature or Peyronie’s disease; the Khera study is in its reference list.
12. European Medicines Agency, Finasteride- and dutasteride-containing medicinal products: referral. The review’s measures were endorsed on 19 June 2025. It covered suicidal thoughts and behaviours only. The page does not mention the penis.
13. Uloko M. Common drug-induced sexual dysfunction in men, Perspectives in Urology: Point-Counterpoint, 10 March 2023, San Diego; video published by Grand Rounds in Urology. This page plays an extract only, from 0:00 to 0:57: her opening on PFS, up to the point where she says sexual medicine has opened its mind to the idea that the condition exists. Her list of symptoms, with “penile shrinkage” in it, follows at about 1:10, outside the extract. Her words are paraphrased from the automatic captions. Her closing advice comes near the end of the full talk, outside the extract; Grand Rounds in Urology’s own summary says she recommends “validating patient concerns”.
14. International Society for Sexual Medicine, What is Erectile Dysfunction?, December 2022. This page plays an extract only, from 1:14 to 2:35.
15. Connor’s story, his own account, written for this site and published in August 2024. The views in it are his own.