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The Truth About Finasteride Side Effects

the truth about finasteride side effects

Finasteride, the active chemical in Propecia and Proscar, is commonly prescribed by doctors to treat male pattern baldness. Do a quick Google search, though, and you’ll quickly find horror stories from people who’ve used it as a hair loss treatment only to suffer terrible side effects – some irreversible. At the same time, numerous trials and studies have shown it to be very safe. So what exactly is the truth about finasteride side effects?

What is finasteride?

Finasteride is a drug prescribed by doctors to treat male pattern baldness (and benign prostatic hyperplasia, but we won’t talk about that here).


It works by inhibiting the enzyme 5-alpha reductase, preventing testosterone from being converted to dihydrotestosterone (DHT).

DHT is considered to be the hormone responsible for androgenetic alopecia (male pattern baldness). DHT binds to hormone receptors in the hair follicles, causing them to shrink and eventually stop producing hair.

So, to put it simply, finasteride lowers levels of the hormone responsible for hair loss.

If you’ve already looked into hair loss treatments, you may have heard it called by another name: Propecia.

propecia finasteride side effects

Propecia is the brand name for 1mg finasteride tablets. This dosage is prescribed as a daily pill to prevent hair loss.

Finasteride is also available in 5mg tablets (brand name Proscar). This dosage is prescribed to treat benign prostatic hyperplasia, although hair loss sufferers can often acquire it off label and split the tablet to reduce costs.

Taking 1mg of finasteride daily reduces DHT levels in the scalp by around 70%.

This is enough to stop, slow, and even reverse hair loss for the majority of users.

It’s FDA approved and has been proven in numerous studies (such as this one and this one) to be an effective hair loss treatment.

Finasteride side effects

Finasteride has been proven to be a highly effective hair loss treatment. But, like pretty much every drug, it has the potential to cause side effects.

Among the side effects listed by Merck, the manufacturer of Propecia, are:

  • Impotence
  • Lack of interest in sex
  • Difficulty achieving orgasm
  • Abnormal ejaculation
  • Swelling or tenderness in the breasts
  • Dizziness

The most common, and controversial, of these side effects are those related to sexual function.

See, as well as reducing scalp DHT levels, finasteride also reduces serum DHT levels by around 70% too.

And the DHT hormone does more than simply cause hair loss in men.

Dihydrotestosterone (DHT)
Dihydrotestosterone (DHT)

DHT is an important male sex hormone, around 5 times more potent than testosterone. During embryogenesis, for example, it plays an essential role in the formation of male genitalia. In rare cases, some males are born with congenital 5-alpha reductase deficiency (and therefore no DHT), resulting in pseudohermaphroditism.

It’s easy to see how finasteride, by lowering DHT, could cause problems with sexual function in males.

A quick Google search of ‘finasteride side effects’ will yield pages and pages of horror stories from users of the drug. Many report sexual side effects – some of which persist even after stopping the drug. This may lead the reader to suspect that the incidence of side effects from finasteride is very high.

In the original trial of finasteride, these side effects were reported to appear in just 2% of subjects.

However, a recent study has cast doubt on the validity of this claim. It found that, of 34 clinical trials, not a single one had adequate safety reporting. Among the most shocking findings were:

  • 53% disclosed conflicts of interest
  • 56% received funding from the manufacturer
  • 76% had a drug safety evaluation duration of less than 1 year

If true, the incidence of sexual side effects from Propecia/finasteride could be much higher than the originally stated 2%.

The truth about finasteride side effects

If you spend enough time on the forums, you’re likely to be scared off the idea of taking finasteride.

After all, it’s not worth losing your sexual function just to maintain your hair. And there certainly seems to be plenty of people reporting negative effects from the drug.

However, it’s important to remain objective when weighing up the pros and cons of finasteride as a hair loss treatment. There are legitimate concerns, yes, but these anecdotal online reports don’t form the most reliable body of evidence.

For one, the people most likely to report on their experience of finasteride are going to be those who’ve had an extreme reaction to it. If you’ve experienced terrible side effects you’re far more likely to shout about it online than if everything goes as expected. This is likely to skew the perception of how dangerous it is.

And this is likely to perpetuate further side effects. The more people read about the terrible side effects of finasteride, the more anxious they are going to be about taking it and the more likely they are to suffer side effects. Placebo is a powerful drug.

This is not to diminish the reports of those who have suffered side effects. Many reports will indeed be genuine, but these reports need to be looked at in context.

This trial, for example, found that:

“Our results support the clinical impression that sexual side effects are actually much less common than reported in clinical trials. The sexual function of all patients remained stable during treatment with 1 mg of finasteride.”

And this trial in particular provides useful insights into the potential sexual side effects of Finasteride. Sleep-related erections were assessed with comprehensive polysomnography to determine whether finasteride had any effect. It’s pretty difficult for the placebo effect to be blamed for these results, as the subjects were asleep! The study found:

“Thus, F[inasteride] did not consistently suppress sleep-related erections compared to P[lacebo]. F[inasteride] primarily inhibits type 2 5 alpha-reductase activity; however, type 1 5 alpha-reductase is the major enzyme in the central nervous system. Therefore, DHT involvement in the maintenance of libido and potency is not excluded.”

As for the aforementioned study which found finasteride safety trials to be flawed, it too could be said to have a conflict of interest: it was funded by the Post-Finasteride Syndrome Foundation.

Should I take finasteride as a hair loss treatment?

Finasteride is one of the most effective hair loss treatments currently available.

It is effective in preventing further hair loss and, for some, can actually be effective for regrowing hair:

finasteride results finasteride side effects
Hair improvement after 12 months on Propecia

But the risks are real. People do suffer side effects from finasteride. Drugs affect different people differently.

That said, it’s probably not as dangerous as some would have you believe.

Propecia was approved as a hair loss treatment in 1997, so it’s been around a while. It’s undergone many trials and has been shown to be safe. It’s also been shown to be effective.

However, it’s far from a perfect drug. Lowering systemic levels of DHT – a major male hormone – is not ideal. Especially when certain unapproved compounds show promise for reducing DHT levels locally.

On balance, though, it’s worth at least trying if you’re concerned about hair loss.

Keep an open mind, try it out for a few weeks, and discontinue finasteride if you experience side effects.

Worried about side effects? Questions about Propecia? Discuss them in the forum!

7 thoughts on “The Truth About Finasteride Side Effects

  1. they are true but i want my hair back

  2. I have started taking 1mg Finasteride for a week and I could feel some side effects about sexual interest and erection problems. The orgasm is like ruined orgasms. I don’t know if it’s a placebo effect or if it’s actually affecting my sexual function because I’ve only started taking it for a week.

    1. I have the same feeling with you,about the side effects.

  3. This is a crazy drugEVERYBODY has side effects expeciay dizziness and headaches. My husband was sick for weeks and had to go off then, once he stopped, he was fine

  4. I am using this 1mg its good.getting my hair back

  5. I am noticing a difference in only two weeks… That being said, the drug makes me feel dizzy, sleepy and disoriented. I read this is a common side effect during the first month since the body is getting acquainted to the drug. It should go away, hopefully.

    It does work perfectly fine.

  6. I had used propecia for 6 years whilst I was single and it helped with my hairloss. I stopped about 7 years ago when I found I had problems with ed and read it could be a side effect of finasteride. I’ve been in a relationship for 8 years now and I still cannot have proper Intercourse without the help of other drugs.
    This was never the case before I
    started using propecia.
    This side effect is very real, and would recommend not to use this treatment for hairloss!

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