PFS — when the side effects don't stop
Finasteride is prescribed to millions of men for hair loss. For a minority, symptoms continue long after the medication is stopped.
What is Post-Finasteride Syndrome?
Post-Finasteride Syndrome (PFS) is a constellation of persistent sexual, neurological, and physical symptoms that continue — sometimes indefinitely — after stopping finasteride, a drug prescribed for hair loss (Propecia, 1mg) and enlarged prostate (Proscar, 5mg).
Finasteride blocks 5-alpha reductase, an enzyme that converts testosterone to DHT (dihydrotestosterone). While this reduces hair loss, it also disrupts neurosteroid production in the brain — hormones critical for mood, cognition, sexual function, and sleep.
Research by Prof. Roberto Melcangi at the University of Milan has shown that these disruptions can cause epigenetic changes — alterations to how genes are expressed — that research suggests may persist long after the drug has cleared the body.
Symptoms of PFS
PFS affects sexual, neurological, and physical health. Symptoms can appear during treatment or after stopping.
Sexual
- Complete loss of libido
- Erectile dysfunction
- Weak or pleasureless orgasms
- Genital numbness
- Reduced ejaculate volume
Neurological
- Severe brain fog
- Memory impairment
- Insomnia
- Emotional numbness
- Depersonalization
Physical
- Chronic fatigue
- Muscle wasting
- Joint pain
- Skin thinning
- Gynecomastia
PFS by the numbers
US finasteride prescriptions per year
Source: FDA prescription dataFDA labelling updated to note effects may persist
Source: FDA label revision historyOf surveyed PFS patients report low libido
Source: PFS Foundation patient survey (self-selected sample)Genes with altered expression in PFS patients
Source: Journal of Sexual Medicine, 2021The reported numbers are likely an undercount
The FDA estimates that only 1–10% of adverse drug reactions are ever reported, and academic studies put the figure lower still. On that basis the 11,557 FAERS reports are likely to represent a fraction of the people affected.
Reporting is also spread across countries and coding systems. One patient's symptoms may be recorded under several separate organ-class codes — sexual dysfunction in one, mood in another, cognition in a third — which makes a single underlying pattern hard for any one database to show. Establishing the true prevalence remains an open research question.
Regulatory timeline
How the regulatory picture has developed since finasteride was first approved.
Proscar approved (5mg)
FDA approves finasteride for enlarged prostate. Side effects described as reversible.
Propecia approved (1mg)
Low-dose finasteride approved for male pattern hair loss. Labelling at the time did not mention persistent effects.
FDA adds persistent effects warning
Labelling updated to state that sexual side effects "may persist after discontinuation".
Post-Finasteride Syndrome coded in MedDRA
PFS added as a term in the dictionary used to code adverse events worldwide, making it possible to record consistently.
FDA adds suicidal ideation warning
31 years after initial approval. Added after mounting evidence and patient advocacy.
EMA mandates patient card
European patients must receive a card describing the risk of persistent effects before starting treatment.
Key research
Independent researchers are uncovering the mechanisms behind PFS — without any known funding from Merck.
Melcangi et al. (2013–2024) — Neurosteroid alterations
Multiple studies from the University of Milan showing PFS patients have significantly altered neurosteroid levels in CSF, plasma, and feces. Neurosteroids regulate mood, cognition, and sexual function.
Csoka & Szyf (2009) — Epigenetic changes
Demonstrated that 5-alpha reductase inhibitors can cause persistent DNA methylation changes, explaining why effects continue after the drug clears the body.
Khera et al. (2014) — Androgen receptor overexpression
Baylor College of Medicine study showing overexpression of androgen receptors in penile tissue of PFS patients — the body's failed compensation for the drug's effects.
Melcangi et al. (2021) — Gut microbiome
Significant changes in gut microbiome composition in PFS patients, suggesting a gut-brain axis connection to neurological symptoms.
What your doctor won't tell you
The gap between what prescribers say and what the evidence shows.
"Side effects are rare and reversible."
In 2011 the FDA required labelling to state that sexual side effects "may persist after discontinuation". A 2017 study found persistent erectile dysfunction in 1.4% of young men after a median of 205 days of use.
"It only affects a small percentage."
With 7 million+ US prescriptions per year, even a 1% rate means tens of thousands of new cases annually. The FDA estimates that only 1–10% of adverse reactions are ever reported — meaning the true number of affected patients could be 10 to 100 times higher than the 21,000+ reports filed with WHO VigiBase across 153 countries.
"There's no proven mechanism for persistent effects."
Multiple peer-reviewed studies have identified epigenetic changes, neurosteroid alterations, androgen receptor overexpression, and gut microbiome disruption in PFS patients. The research exists — yet to date, Merck has not publicly funded any of it.
"It doesn't affect mental health."
In 2023, 31 years after initial approval, the FDA added a suicidal ideation warning to finasteride's label. Depression, anxiety, cognitive impairment, and emotional numbness are among the most commonly reported persistent symptoms.
Current treatment landscape
An honest assessment of where things stand — and why there is reason for cautious hope.
Important: There is currently no FDA-approved treatment for PFS. No pharmaceutical company has funded research into treatment. All information below is based on independent research and patient-reported experiences.
The Milano Project — most promising avenue
Prof. Roberto Melcangi's research at the University of Milan has identified allopregnanolone — a neurosteroid depleted in PFS patients — as a potential therapeutic target. Animal studies have shown that allopregnanolone supplementation can reverse some finasteride-induced changes. This is the most advanced research programme and is funded entirely by patient donations through the Milano Project.
What some patients report
While no treatment is proven, some patients report partial improvement with lifestyle modifications. These are not recommendations — they are observations from patient communities:
- Regular exercise (particularly resistance training)
- Sleep optimisation and stress reduction
- Dietary changes (anti-inflammatory diets)
- Time — some patients report gradual, partial improvement over months to years
How to get help
You don't have to face this alone. Here's where to start.
WhatsApp support groups
Connect with other PFS patients in private, moderated groups. Share experiences and coping strategies with people who understand.
Join the patient registry
Add your case to the SIDEfxHUB registry. Your anonymized data helps researchers understand PFS and work toward treatment.
Report your side effects
Filing a report with your national regulator (FDA, MHRA, EMA) is critical. Low reporting rates make the drug appear safer than it is.
Support library
Research papers, patient stories, media coverage, and practical resources — all in one place.
Hear from PFS patients
Real patients sharing their experiences with Post-Finasteride Syndrome.
Mark's Story
Mark has been suffering with the devastating effects of finasteride for over two years.
Sam's Story
One pill destroyed Sam's life. He shares his experience with finasteride side effects.
20 Years of PFS
A patient who has been suffering from PFS for over 20 years shares his journey.
Sources & databases
All data on this page is sourced from peer-reviewed research and official regulatory databases.
FDA FAERS
The FDA Adverse Event Reporting System — the primary US database for drug safety reports.
Visit database ↗WHO VigiBase
The WHO global database of individual case safety reports — over 30 million reports from 153 countries.
Visit database ↗PubMed — PFS Research
Search peer-reviewed publications on Post-Finasteride Syndrome on the NIH database.
Search PubMed ↗PFS Foundation
The leading organisation funding PFS research, including the Milano Project with Prof. Melcangi.
Visit website ↗EMA — Finasteride Review
European Medicines Agency's safety review of finasteride-containing products.
View review ↗RxISK
Independent drug safety research organisation. Report side effects and access drug safety data.
Visit website ↗I think I have PFS. What now?
If you recognise these symptoms, here are 5 steps you can take right now.
Connect with others
Join a WhatsApp peer support group — talk to people who understand exactly what you're going through.
Report your side effects
Report to your country's health regulator. Every report makes these conditions harder to ignore.
Read about managing symptoms
Visit our Support Library for guides on coping strategies, talking to your doctor, and lifestyle approaches.
Join the registry
Register your experience anonymously. Your data supports research and helps prove the true scale of these conditions.
Think you have PFS?
You are not alone. Join the registry, connect with other patients, and help drive the research that could lead to treatment.