Is post-finasteride syndrome autoimmune?

Heard that post-finasteride syndrome (PFS) might be autoimmune? Nobody knows. We found no published study that has tested people with PFS for an immune attack on their own body, so for now it’s a hypothesis.

What does exist is a handful of small studies with signs of inflammation. The most striking came from one study of penile skin. In men with PFS, genes that drive immune cells and inflammatory signals were more active than in men without it.

The UK Propecia leaflet already lists erection, sex drive and ejaculation problems that persisted after stopping. What keeps them going is still unknown, and the immune idea is one attempt to explain it.

How far does the evidence for it go?

What would it mean for PFS to be autoimmune?

It would mean the immune system attacks the body’s own tissue and keeps doing so after the last tablet. That’s what happens in conditions such as rheumatoid arthritis and lupus.

To show this, researchers look for the attack itself: antibodies or immune cells aimed at a person’s own tissue. No published PFS study we know of has looked for them. Inflammation alone isn’t proof, because it also follows infection, injury and stress.

PFS is also more than a sexual problem. Doctors and researchers who proposed criteria for PFS in 2022 list problems with cognition, depression and suicidality alongside the sexual symptoms. Any explanation, immune or not, has to cover all of that. If you’re struggling, the Samaritans are on 116 123 in the UK, free, at any hour.

Is there inflammation in people with PFS?

There are signs of it in one study of gene activity. A team at Baylor College of Medicine in Texas compared penile skin from 26 men with PFS and 26 men without it.

Thousands of genes were more or less active in the men with PFS. Among them, the authors report, pathways controlling T-cell development and cytokine signalling were turned up. T cells are immune cells, and cytokines are the chemical signals they use to drive inflammation.

The authors name the limits themselves. Gene activity isn’t the same as disease, the samples came from one tissue, and nobody had samples from before the men took finasteride. They say the study can’t show cause.

The same men also had more activity in the gene for the androgen receptor, the protein that lets cells respond to testosterone and DHT. An Italian study counted more cells carrying that receptor in the foreskin of 8 men with lasting symptoms than in 11 men who had never taken finasteride.

One idea is that the immune system attacks this receptor. That’s a guess nobody has tested. Raised immune activity can have many causes, and neither study looked for an attack on the body’s own tissue.

Is the gut involved?

Possibly. A pilot study in Milan compared gut bacteria in people with PFS with those of healthy men. The patients had a less varied mix, and a smaller group of them had fewer of some types of bacteria.

The same team then gave rats finasteride for 20 days and stopped it. A month later, the rats had signs of inflammation in the colon. A follow-up study found inflammation in the hypothalamus too, a part of the brain that helps control hormones and sex drive.

Rats aren’t people, and a pilot study is small. These findings point researchers somewhere to look. They don’t show that the same happens in humans. Our article on the gut study covers it in more detail.

What can I do?

Finasteride helps many people with hair loss or an enlarged prostate. If you have side effects, that’s a decision for you and your prescriber. The leaflet says to stop and see a doctor if your mood changes.

If problems haven’t lifted since you stopped, tell your GP your dates: “Finasteride 1 mg from January 2023, last tablet March 2024.” Note every change, such as joint pain, gut problems or tiredness. Say how things were before. Many people say it took time to be taken seriously. You can report it without a doctor agreeing.

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. 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?

Would immune treatments help PFS? Nobody knows, because no trial has tested them in PFS. Medicines that damp down the immune system carry real risks of their own. Talk to a doctor before taking anything, and be wary of anyone who sells a cure.

Can finasteride cause allergic reactions? Yes, the UK leaflet lists them: swelling of the lips, face or throat, hives and difficulty breathing. It says to stop and talk to a doctor immediately. That’s a reaction while taking the tablets, which is a different question from lasting symptoms after stopping.

Do all researchers accept PFS? No. A 2026 analysis followed older men from a large prostate cancer trial for about 20 years. Those on finasteride had no more of 22 conditions linked to PFS than those on a dummy pill, and the authors concluded this doesn’t support PFS. Other researchers keep studying it, and the UK leaflet lists sexual problems that persisted after stopping.

If you live with PFS, your report adds to the record researchers draw on. Report it, even years after your last tablet.

Sources

1. Propecia 1 mg film-coated tablets, patient information leaflet, electronic medicines compendium (emc), last revised May 2026. Section 4, “Frequency unknown”: persistent erection, sex drive and ejaculation problems “after discontinuation of treatment”. Also in section 4: allergic reactions (swelling of lips, face, tongue and throat, hives, breathing difficulties): “Stop taking Propecia and talk to your doctor immediately.” Section 2: mood alterations; stop and contact your doctor.
2. Healy D, Bahrick A, Bak M, et al. Diagnostic criteria for enduring sexual dysfunction after treatment with antidepressants, finasteride and isotretinoin. Int J Risk Saf Med 2022;33(1):65-76. Proposed criteria; cognitive impairment, depression and suicidality listed alongside the sexual problems in PFS.
3. Howell S, Song W, Pastuszak A, Khera M. Differential gene expression in post-finasteride syndrome patients. J Sex Med 2021;18(9):1479-90. Case-control, single centre, 26 patients and 26 controls. In penile skin, 1,446 genes were over-expressed and 2,318 under-expressed, and androgen receptor expression was higher. The discussion reports upregulated pathways for T-cell development, proliferation and function and for cytokine signalling. Limits stated by the authors: selection bias, no samples before exposure, penile tissue only, no mechanistic data to imply causality.
4. Borgo F, Macandog AD, Diviccaro S, et al. Alterations of gut microbiota composition in post-finasteride patients: a pilot study. J Endocrinol Invest 2021;44(6):1263-73. Faecal samples from 21 patients analysed against 10 healthy men; lower diversity; muscular problems reported by more than half of the patients.
5. Diviccaro S, Giatti S, Cioffi L, et al. Gut inflammation induced by finasteride withdrawal: therapeutic effect of allopregnanolone in adult male rats. Biomolecules 2022;12(11):1567. Rats; 20 days of finasteride, then one month without; raised IL-1β and TNF-α in the colon.
6. Diviccaro S, Oleari R, Amoruso F, et al. Exploration of the possible relationships between gut and hypothalamic inflammation and allopregnanolone: preclinical findings in a post-finasteride rat model. Biomolecules 2025;15(7):1044. Rats; colonic inflammation and raised hypothalamic markers of neuroinflammation after withdrawal.
7. Di Loreto C, La Marra F, Mazzon G, et al. Immunohistochemical evaluation of androgen receptor and nerve structure density in human prepuce from patients with persistent sexual side effects after finasteride use for androgenetic alopecia. PLoS One 2014;9(6):e100237. 8 cases and 11 controls; higher density of nuclear androgen receptor in stromal and epithelial cells of the foreskin.
8. Till C, Tangen CM, Goodman P, Unger JM, Thompson IM Jr. No evidence of post-finasteride syndrome in 267,983 person-years follow-up in the Prostate Cancer Prevention Trial. Urology 2026;216:59-64. Trial records linked to Medicare claims; median follow-up 20 years; none of 22 conditions significantly associated with the finasteride arm.