Finasteride Side Effects: Wimbledon GP Answers Your Questions

I'm Dr Umer Malik, a GP at Mayfield Clinic Wimbledon. Finasteride is a prescription medicine used to treat male pattern hair loss and an enlarged prostate. Some men obtain it through private or online prescribing services. Although many people take finasteride without problems, it can cause side effects, including changes in sexual function or mood. In May 2026, the UK medicines regulator (MHRA) strengthened its safety warnings about finasteride and a related medicine, dutasteride. In my clinic room in Wimbledon, I'm regularly asked about these side effects, so I've put together answers to the questions patients raise most often.

Understanding finasteride and its possible side effects

What is finasteride, and why do men take it?

Finasteride is a prescription-only medicine, usually taken once a day. The 1 mg dose is used for male pattern hair loss, while the 5 mg dose is used for an enlarged prostate.

It works by blocking an enzyme involved in converting testosterone into dihydrotestosterone (DHT). DHT contributes to male pattern hair loss and prostate growth.

In the UK, finasteride for hair loss is generally obtained privately rather than through routine NHS prescribing. Some people access it through online prescribing services. Treatment does not work immediately. It may take several months to notice a benefit, and hair loss may gradually resume after stopping.

Can finasteride cause erectile dysfunction or other sexual side effects?

Yes. Recognised side effects include difficulty getting or maintaining an erection, reduced interest in sex, and changes in ejaculation, including a reduced amount of semen.

The NHS describes these sexual side effects as common, meaning they affect more than 1 in 100 people taking the medicine. Individual experiences vary, and not everyone develops side effects.

Some people have reported sexual symptoms continuing after stopping finasteride, and the MHRA has highlighted the possibility of persistent symptoms in its safety advice. Reports like these show that a problem has been reported, but on their own they cannot show how often it happens.

Erection problems can have several causes, including medication effects, diabetes, cardiovascular risk factors, stress and hormonal conditions. Finasteride may be relevant, but it should not automatically be assumed to be the cause.

If you notice changes in sexual function, speak to your prescriber or GP. A review can help consider possible causes and discuss appropriate next steps. Finasteride has also been associated with breast changes. The NHS advises contacting your doctor or NHS 111 promptly if you notice a breast lump, pain, swelling or nipple discharge.

Can finasteride affect my mood?

The MHRA states that finasteride is associated with depression, suicidal thoughts and sexual dysfunction, which may persist after treatment is stopped. Its May 2026 update also said that the product information for finasteride 1 mg would note that sexual dysfunction may contribute to mood disorders.

If you take finasteride 1 mg for hair loss and develop depression or suicidal thoughts, the MHRA advises you to stop taking it and contact your doctor as soon as possible. If you take the 5 mg dose for an enlarged prostate, it advises contacting your doctor as soon as possible for advice.

It may help to tell someone you trust that you take finasteride, so they can support you and may notice changes in your mood.

If you feel at immediate risk of harming yourself, call 999 or go to A&E. If you need urgent medical advice, contact NHS 111. You can also call Samaritans free on 116 123 at any time for emotional support.

Should I stop finasteride, and will the side effects go away?

The appropriate next step depends on your symptoms, why you take finasteride and your individual circumstances.

If you develop depression or suicidal thoughts while taking the 1 mg hair-loss dose, follow the MHRA advice above to stop taking it and contact your doctor as soon as possible. If you experience sexual side effects, speak to your prescriber or GP to discuss whether stopping or changing treatment is appropriate. If you take the 5 mg dose for an enlarged prostate, seek medical advice before changing your treatment, and contact your doctor as soon as possible if you develop symptoms of depression or suicidal thoughts.

For people taking finasteride for hair loss, the benefits may gradually diminish after stopping, and hair loss may resume. Your prescriber can discuss the possible benefits and drawbacks of continuing or stopping treatment.

Many side effects improve, but some people report symptoms continuing after they stop. How long symptoms last can vary, and a GP can assess ongoing symptoms and look at all possible causes.

Anyone can report a suspected side effect through the MHRA Yellow Card scheme. It may be helpful to note when you started or stopped taking finasteride, when symptoms began, and whether they changed after stopping. This information can also help your GP assess your symptoms.

What will a GP check, and when should I book?

Your GP will usually start by asking about your symptoms, when they began in relation to finasteride, your medical history and other medicines. Depending on your circumstances, they may also ask about mood, sex drive, morning erections, alcohol, smoking, stress and other relevant factors.

Erectile dysfunction can sometimes be an early indicator of an underlying condition, including diabetes or cardiovascular disease. Your GP may therefore check your blood pressure and assess your overall health and cardiovascular risk.

Depending on your symptoms and assessment, blood tests might include HbA1c, to assess for diabetes, cholesterol, as part of a cardiovascular risk assessment, testosterone, if clinically indicated (testing is generally done in the morning, and a low result usually needs confirmation with a repeat test), and other hormone tests, such as prolactin or oestradiol, where there is a specific clinical reason.

Not everyone needs all these tests. Your GP can advise which investigations are appropriate and whether any results need repeating.

Finasteride can also lower PSA (prostate-specific antigen), a blood marker used when assessing prostate health. The effect varies, but levels may be reduced substantially during treatment. Tell your doctor if you currently take finasteride or have taken it previously, so they can interpret the result in context.

Consider booking a GP appointment if you have erection problems, reduced sex drive, ejaculation changes, mood symptoms or other concerns while taking finasteride, or if symptoms continue after stopping. A GP can assess possible causes, discuss appropriate investigations and agree a plan, including referral where needed.

This article provides general information and is not a substitute for individual medical advice. If you take finasteride for an enlarged prostate, speak to your doctor before changing your treatment. If you are in immediate danger or at risk of harming yourself, call 999 or go to A&E.

Dr Umer Malik MBBS, BSc, MRCGP, MPH has 17 years of postgraduate clinical experience as a doctor, including nine years as a fully qualified GP. He sees patients at Mayfield Clinic Wimbledon.

If you'd like to discuss finasteride side effects or any other health concern, you can book a private GP appointment at Mayfield Clinic Wimbledon or discuss related concerns through our sexual health service.