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Finasteride side effects: Everything you need to know

Finasteride side effects: Everything you need to know

Stefano Mirabello NowPatientGreen tick
Created on 4 Sep 2023
Updated on 16 Jul 2024

In a world of dubious hair loss treatments, finasteride is one of the exceptions. It’s a medically proven hair loss treatment that works. Finasteride can slow male pattern baldness and even help regrow lost hair.

But like all medical treatments finasteride can have side effects. Usually these side effects are mild and short‐lasting but they can interfere with your sex life. And in rarer cases they can be more serious. So you need to know about them.

Here we explain what side effects finasteride can cause, how common they are, and what you can do about them.

What is male pattern baldness?

Male pattern baldness (MPB) is the most common cause of hair loss in men. Around 50% of us develop it by age 50. But it gets plenty of us when we’re younger. In our 30s, 20s, or even earlier. Yikes!

Hair loss usually follows a pattern, thinning and receding along your hairline and on the top of your head first. Eventually most guys are usually left with a bald head but with plenty of hair around the sides and back. MPB is caused by a combination of ageing, genetics, and hormones.

The hormone DHT (dihydrotestosterone) is the main culprit. DHT attacks hair follicles in your scalp, causing them to shrink over time, producing thinner and shorter hairs and eventually no hair at all.

How does finasteride fight male pattern baldness?

Finasteride – also sold under the brand name Propecia – fights MPB by lowering how much DHT you have in your scalp. It blocks an enzyme (called type II 5α-reductase) that converts testosterone into DHT, reducing how much DHT is made in your scalp.

What are the side effects of finasteride?

As with all medications finasteride can cause unwanted side effects. Finasteride is a safe and well‐tolerated medication for most men. It has been put through a series of rigorous clinical trials and is approved by healthcare agencies all over the world.

Most men who take finasteride don’t experience side effects. And those that do can experience different side effects from other guys. Finasteride side effects are usually mild and pass as your body gets used to the medication. However, some men can experience more severe and long-lasting side effects.

Finasteride and sexual side effects

The three most common side effects of finasteride found in clinical trials were sexual. They were:

  • Erectile dysfunction (not being able to get or maintain an erection that’s firm enough for sex)
  • A reduced sex drive (less desire to have sex)
  • A reduction in the amount of semen produced at ejaculation

These side effects can happen because finasteride can cause some of your testosterone to be converted to a hormone called estradiol. Estradiol is a form of estrogen (a female sex hormone) which can cause sexual problems in some men.

What? A female sex hormone? ED? Less desire for getting down? Don’t worry. The truth is although these are the most common side effects caused by finasteride they are still relatively uncommon. In clinical trials they affected around 1% of men who took 1 mg finasteride tablets and around 10% of men who took 5 mg tablets.

Other finasteride side effects

Rarer side effects of finasteride that affect less than 1% of the men who take it include:

  • Skin rashes
  • Swelling or tenderness in the chest

Even rarer side effects of finasteride include:

  • Allergic reactions
  • Heart palpitations
  • Pain in the testicles
  • Depression
  • Anxiety

How common are the side effects of finasteride?

Most men who take finasteride won’t experience any side effects at all with even the most common ones affecting 10% of men or less. However, the side effects of finasteride do become more common if you take the stronger 5 mg tablets rather than the 1 mg tablets.

  • Around 1% of men who take the 1 mg tablets experience the most common sexual side effects. Around 10% of men who take the 5 mg tablets experience them
  • Around 1% of men who take the 5 mg tablets experience skin rashes and chest tenderness. Less than 1% of men who take the 1 mg tablets experience these side effects
  • Less than 1% of men (often far less) experience other side effects when taking Finasteride

Finasteride long term side effects

There are very few reported long-term effects of taking finasteride. Most side effects pass as your body adjusts to the treatment. A small number of men do continue to experience the sexual side effects of finasteride for as long as they take it although the exact number of men is unknown.

We also need to talk about something called post-finasteride syndrome (PFS).

Most finasteride side effects vanish if you stop taking it. But PFS is the name given to side effects that continue after you stop taking finasteride. These are usually the sexual side effects but some men report they have other side effects too (depression and anxiety) that continue long after they stop taking finasteride.

However, there’s a lot of controversy around PFS. Some experts think it’s extremely rare whilst some experts argue PFS doesn’t exist at all and that the side effects are caused by something other than finasteride. PFS is something to be aware of but until more research is done on it no one can say for sure if it is real or how many men it affects.

Does finasteride cause cancer?

You may have read online about links between finasteride and cancer, including a finasteride prostate cancer risk.

This mostly comes from a piece of research in 2003 that showed men who took finasteride were more likely to develop high grade prostate cancer. However, increased rates of cancer weren’t found in clinical trials for finasteride. Other research that investigated the long-term effects of finasteride didn’t find higher rates of cancer – one even found lower rates of prostate cancer amongst men who took finasteride.

Research into the long-term effects of finasteride is continuing but today there is no good reason to think that finasteride causes cancer.

How to reduce the side effects of finasteride

If you do experience any side effects from taking finasteride then don’t panic as there’s plenty you can do to reduce or get rid of them. This includes:

  • Reducing your dose of finasteride
  • Trying an erectile dysfunction treatment
  • Making positive lifestyle changes

Read more on how to reduce the side effects of finasteride.

Finasteride side effects FAQS

1. Does finasteride cause dizziness?

Finasteride can cause dizziness or light-headedness but this is a rare side effect that affects far less than 1% of men who take finasteride.

2. Why does finasteride cause impotence?

Finasteride works by reducing how much testosterone is converted into a hormone called DHT, which causes male pattern baldness. However, finasteride can cause some testosterone to be converted into estrogen. Having higher estrogen levels can cause sexual side effects in some men, like a lower sex drive and erectile dysfunction (impotence).

3. Are the side effects of finasteride reversable?

Most of the side effects caused by Propecia (finasteride) vanish if you stop taking it. In extremely rare cases some men have reported they have side effects that last after they stop taking Propecia. It’s not known how many men this happens to or even if these side effects are really caused by Propecia. It may be that they have another cause and are mistakenly attributed to Propecia.

4. What does finasteride do to the body?

Finasteride reduces how much of your testosterone is converted into a hormone called DHT (dihydrotestosterone). DHT can shrink the follicles in your scalp, making them produce finer hairs and eventually no hair at all. By reducing how much DHT you have in your body finasteride slows or stops DHT shrinking your hair follicles.


Medical Disclaimer

NowPatient has taken all reasonable steps to ensure that all material is factually accurate, complete, and current. However, the knowledge and experience of a qualified healthcare professional should always be sought after instead of using the information on this page. Before taking any drug, you should always speak to your doctor or another qualified healthcare provider.

The information provided here about medications is subject to change and is not meant to include all uses, precautions, warnings, directions, drug interactions, allergic reactions, or negative effects. The absence of warnings or other information for a particular medication does not imply that the medication or medication combination is appropriate for all patients or for all possible purposes.

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