How dangerous is Propecia? The lasting risks

Thinking about Propecia for hair loss, or already taking it? The UK leaflet calls sexual side effects from Propecia (finasteride) uncommon. It also lists erection, sex drive and ejaculation problems that can last after stopping, and patients call this post-finasteride syndrome (PFS).

Nobody has measured how often the lasting problems happen. The leaflet files them under “Frequency unknown”, and that is the honest answer to how dangerous it is.

Sam took finasteride to stop his hair falling out. His GP told him erection problems might happen. Was anything said about them lasting? “Nothing permanent,” he says. Watch from 3:56 to hear the warning he was given.

Play video: The Hidden Devastation of Finasteride – Sam’s Story

So what does the leaflet list, and what can you do if side effects stay?

What side effects does Propecia have?

The UK leaflet lists sexual, mood and some lasting side effects. Propecia works by blocking an enzyme called 5-alpha reductase. That enzyme turns testosterone into DHT, the hormone that shrinks hair follicles in male pattern baldness. Less DHT means slower hair loss.

The same enzyme does other jobs. In the brain it helps make neurosteroids, such as allopregnanolone, which affect mood. Researchers studying PFS think this may be part of why some men describe changes in mood and cognition. That is still being studied, and our page on neuroactive steroids in PFS explains one study.

The UK leaflet for Propecia 1 mg lists less desire for sex, erection problems and less semen. Each is “uncommon”, which means up to 1 in 100 people.

The lines most men never read sit under “Frequency unknown”:

• “persistent difficulty having an erection after discontinuation of treatment”
• “persistent decrease in sex drive after discontinuation of treatment”
• “persistent problems with ejaculation after discontinuation of treatment”

It also lists depression and suicidal thoughts. For low mood or suicidal thoughts, it says to stop taking Propecia and contact your doctor as soon as possible. If you’re struggling, the Samaritans are free on 116 123, day or night.

Can the side effects last after stopping?

Yes, for some men. The leaflet says some side effects “disappeared when treatment is stopped”. It also lists the ones that persisted.

PFS is more than sexual problems. The diagnostic criteria proposed in 2022 say cognitive problems, depression and suicidal thoughts can come with the sexual problems, or happen without any sexual difficulties.

One study looked at the medical records of men treated at Northwestern Medicine in Chicago. Among men aged 16 to 42 on the hair-loss dose, about 1 in 125 had erection problems recorded as lasting at least 90 days after stopping. Those who took it longer had the higher risk. Records can miss things, and this shows a link, not proof of cause.

For some people it has lasted years after stopping. Nobody knows yet who will be affected, or whether it will ease. Men with PFS describe a numb, shrunken penis, a flat mood, and problems with concentration and memory.

What did regulators and courts do?

The UK warning grew step by step. Lasting erection problems were added to the product information in 2010, and depression in 2017. In 2024 the MHRA, the UK medicines regulator, announced a card for every pack. In May 2026 it told doctors to explain the risks when they prescribe, and to ask about depression first.

In the US, men took Merck, the maker, to court. NBC News reported in 2017 that at least 1,300 lawsuits had been filed. Merck said it “stands behind the demonstrated safety and efficacy profile of Propecia”.

A Reuters investigation looked at company documents from those cases that a court had kept sealed. In 2021 a US judge ordered them unsealed. Our summary of the Reuters reporting has more.

Robb Dixon has PFS. Here he tells ITV’s Good Morning Britain how easy it was to order finasteride online, and what began after he stopped.

Play video: Pharmacists warn against buying prescription drugs online

What can you do if you have side effects?

Propecia helps many men keep their hair. If you have side effects, that’s a decision for you and your prescriber. Follow the leaflet: it says to stop and see a doctor if your mood changes.

Many people say it took time to be taken seriously. Bring the leaflet line to your appointment. 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

Frequently asked questions

Is Propecia the same as finasteride? Yes. Propecia is Merck’s brand of finasteride 1 mg for hair loss. Proscar is the 5 mg brand for an enlarged prostate. Generic finasteride carries the same warnings.

Is Propecia banned? No. It is still licensed in the UK, and the 1 mg dose is sold on private prescription. The MHRA has added warnings and a card for every pack instead.

Does topical finasteride carry the same risks? It contains the same medicine and can reach the blood. Our page on topical finasteride covers what is known so far.

Sam was told “nothing permanent”. If yours has lasted, report it, and read our page on post-finasteride syndrome.

Sources

1. Propecia 1 mg film-coated tablets: patient information leaflet, last revised May 2026, electronic medicines compendium (emc). Section 4: impotence and less desire are “Uncommon: may affect up to 1 in 100 people”. Persistent erection, sex drive and ejaculation problems “after discontinuation of treatment” under “Frequency unknown”. Also: “Some of the side effects are temporary with continued treatment or disappeared when treatment is stopped.” Section 2: stop and contact your doctor for depression or suicidal thoughts.
2. MHRA, Finasteride and dutasteride: updated safety warnings for psychiatric side effects and sexual dysfunction, Drug Safety Update, 11 May 2026.
3. MHRA, Finasteride: review of safety data and expert advice on management of risks, 29 April 2024. Covers the 2010 and 2017 product information changes and the patient card.
4. Healy D, Bahrick A, Bak M and colleagues. 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 from expert agreement. Section 5: cognitive impairment, depression and suicidality “can occur independently of any sexual difficulties but may also accompany sexual problems”.
5. Kiguradze T, Temps WH, Yarnold PR and colleagues. Persistent erectile dysfunction in men exposed to the 5α-reductase inhibitors, finasteride, or dutasteride. PeerJ 2017;5:e3020. Northwestern Medicine records. Men aged 16 to 42 on finasteride 1.25 mg a day or less: 34 of 4,284 (0.8%) developed persistent erectile dysfunction, lasting at least 90 days after stopping. “Risk of PED was higher in men with longer exposure.” Single-group design; an association, not proof of cause.
6. NBC News, Hair loss drug Propecia carries risk of losing something else, 2017. At least 1,300 finasteride lawsuits filed against Merck; Merck’s statement.
7. Reuters, Hidden injustice: how a court let Merck hide secrets about a popular drug’s risks, 2019; and Reuters, Judge orders Merck documents on anti-baldness drug Propecia unsealed, 2021.
8. Moral Medicine, The Hidden Devastation of Finasteride – Sam’s Story, June 2025. Warning from 3:56; “nothing permanent” at 4:32.
9. Good Morning Britain, ITV, Pharmacists warn against buying prescription drugs online, 11 February 2026. Robb Dixon on ordering online from 0:49.

Sources checked on 22 October 2026. AI-assisted writing and review, not clinical review.