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Side effects of finasteride - Brand names: Proscar, Propecia

Like all medicines, finasteride can cause side effects in some people, although not everyone gets them.

Common side effects

These common side effects of finasteride happen in more than 1 in 100 people.

They usually improve after a while, but they can sometimes carry on even after you stop taking finasteride. There are things you can do to help cope with them:

Problems getting an erection and less interest in having sex

Speak to your doctor if you get these side effects.

Problems with ejaculating, such as little or no semen

If the amount you ejaculate is less than usual or you have no semen at all, speak to your doctor.

Serious side effects

Serious side effects are rare and happen in less than 1 in 1,000 people. Some people may notice these side effects after taking finasteride for a few months.

Call your doctor or call 111 now if you get:

  • any lumps, pain or swelling in your chest area or discharge from your nipples – these may be signs of a serious condition such as breast cancer
  • low mood (depression) – if you're taking it for hair loss and you get this side effect, stop taking the medicine straight away

It's important to tell your family or friends that you're taking finasteride, and that it may sometimes affect your mood or behaviour. This is so that they can help you notice any changes.

Immediate action required: Call 999 or go to A&E now if:

  • you have thoughts of harming yourself

Find your nearest A&E

Serious allergic reaction

In rare cases, finasteride may cause a serious allergic reaction (anaphylaxis).

Immediate action required: Call 999 now if:

  • your lips, mouth, throat or tongue suddenly become swollen
  • you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
  • your throat feels tight or you're struggling to swallow
  • your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
  • you suddenly become very confused, drowsy or dizzy
  • someone faints and cannot be woken up
  • a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

Other side effects

These are not all the side effects of finasteride. For a full list see the leaflet inside your medicines packet.


You can report any suspected side effect using the Yellow Card safety scheme.

Visit Yellow Card for further information.

Page last reviewed: 2 August 2023
Next review due: 2 August 2026