Are Finasteride Side Effects Permanent?

Finasteride is a treatment option widely used to treat hair loss (androgenetic alopecia) in men. Men who have androgenic alopecia have a genetically inherited sensitivity to dihydrotestosterone (DHT). This is a hormone in the body that is converted from testosterone by an enzyme: 5 alpha-reductase. If you have this condition, your hair follicles are more sensitive to DHT. This causes your hair follicles to undergo a progressive process of miniaturisation or shrinkage. The hair that is produced by follicles that are affected become smaller in diameter, shorter in length and lighter in colour until eventually the follicles shrink completely and stop producing hair.

The discovery of Finasteride was prompted by a study of a group of pseudohermaphrodites in a remote village in the Dominican Republic. A clinical researcher and Professor of Endocrinology: Dr Imperato-McGinley found that children born with a particular genetic mutation there were resulting in males with apparent female genitalia at birth. These children were raised as girls until puberty at which time male genitalia and characteristics began to form. In their later life, they were found to be like other males in the village except their beard growth remained scanty, they had no acne, they experienced no hairline recession and their prostates remained small. Their condition was found to be caused by a suppressed level of dihydrotestosterone (DHT) secondary to a deficiency in the enzyme 5 alpha reductase. Dr Imperato-McGinley first published her landmark paper in 1974 and her work defined a previously unrecognised clinical disorder: inherited 5 alpha-reductase deficiency. In the subsequent years that followed; eighteen to be precise; her work led to the development of finasteride: the first specific inhibitor of the enzyme 5 alpha-reductase. Today, Finasteride is used for the treatment of enlarged prostates and male hair loss.

Finasteride works because it stops testosterone from being converted into DHT by inhibiting the enzyme 5 alpha reductase. As DHT is the hormone responsible for shrinking or miniaturising the hair follicle leading to hair loss, it is the ability of Finasteride to suppress DHT that gives Finasteride the potential to stop hair loss and cause regrowth of hair.


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What is a side effect and what kind of side effects does Finasteride have?

A side effect is an unwanted reaction or symptom caused by your treatment. Sometimes, you may hear of side effects referred to as adverse effects or an adverse reaction. All medicines carry the risk of side effects. It is worth noting that this does not mean that all medicines cause side effects. Finasteride is no different in this respect. On the whole, Finasteride has been in use since the late nineties and it is known as a well-tolerated treatment option. However, it is important if you are considering Finasteride or have already started it that you are vigilant about the possible side effects so that you are able to recognise them and get advice promptly.

The original manufacturer of Finasteride; Merck Sharp & Dohme Limited say that the side effects experienced with Finasteride (brand name Propecia) usually have been mild and generally have not required discontinuation of therapy. They also go on to say that Finasteride for male pattern hair loss has been evaluated for safety in clinical studies involving more than 3,200 men. In three 12-month, placebo-controlled, double-blind, multicentre studies of comparable design, the overall safety profiles of ‘Propecia’ and placebo were similar. (A placebo is a substance used in medical studies that do not have any active ingredients and is not expected to have any physiological effect. This is used as a control or a comparison when doing studies). Discontinuation of therapy due to any clinical adverse experience occurred in 1.7% of 945 men treated with ‘Propecia’ and 2.1% of 934 men treated with placebo. In these studies, the following drug-related adverse experiences were reported in ≥1% of men treated with ‘Propecia’: decreased libido (‘Propecia’, 1.8% vs. placebo, 1.3%) and erectile dysfunction (1.3%, 0.7%). In addition, decreased volume of ejaculate was reported in 0.8% of men treated with ‘Propecia’ and 0.4% of men treated with placebo. Resolution of these side effects occurred in men who discontinued therapy with ‘Propecia’ and in many who continued therapy. The effect of ‘Propecia’ on ejaculate volume was measured in a separate study and was not different from that seen with placebo. By the fifth year of treatment with ‘Propecia’, the proportion of patients reporting each of the above side effects decreased to <0.3%

In summary, what this shows is that according to their studies which looked at over 3200 men

  • Finasteride at a treatment dose of 1mg was found to have a similar safety profile to placebo.
  • Less than 1.7% (approximately 16 men) of 945 men treated with Finasteride stopped treatment
    due to side effects compared with 2.1%(approximately 20 men) of 934 men treated with placebo.
  • The side effects stopped not only in men that had stopped using Finasteride but also in many of
    those who continued therapy.
  • The percentages of reports of side effects with Finasteride 1mg use are very low.
  • By the 5th year of treatment with Finasteride, the proportion of patients reporting the side effects

listed in the paragraph above had decreased to <0.3%
Listed below are the side effects that have been reported with Finasteride

Common. Side effects that affect between 1 in 10 and 1 in 100 people

Decreased libido (occurs in about 1-2% of men)
Decreased volume of ejaculate

Uncommon. Side effects that affect between 1 in 100 and 1 in 1000 people

Ejaculation disorders
Breast tenderness
Breast enlargement
Please note that if you have noticed that you are experiencing changes in breast tissue such as lumps, pain, enlargement of breasts, or nipple discharge, please seek prompt advice from your doctor. The MHRA published that a Europe-wide review of information from clinical trials, published literature and reports of adverse drug reactions has concluded that an increased risk of male breast cancer associated with finasteride use cannot be excluded. This was based on 3 reports received from the 1mg use of Finasteride for androgenetic alopecia. This was from data gathered from worldwide reporting.

Unknown. These are side effects that occur at a frequency that cannot be estimated from the data that is available.

Hypersensitivity reactions including swelling of the lips, tongue, throat and face, itch and rash. If you think that you are having an allergic reaction to finasteride, seek emergency medical attention.
Depression (If you develop depression, stop finasteride immediately and inform a healthcare
Heart palpitations
Changes in liver enzymes.
Pain in your testicles
Sexual dysfunction
Male infertility
Poor seminal quality
Although it can be daunting to be faced with information about side effects, it is useful to put it into context. Finasteride has been in use since the late nineties and there are many studies that have been conducted with regards to this use. In general, it is regarded to be a well-tolerated drug with low incidences of side effects.

It is important to not only look at what information is available from the manufacturers and individual studies but also literature reviews which consider what the studies can tell us and whether the studies have flaws within them. In a literature review3 conducted in 2016 considering data on the use of finasteride in male pattern baldness, 262 studies were evaluated up to March 2014. Out of these 12 met the criteria to be included in the review. It revealed that that according to the review of the studies conducted, many studies have concluded that the side effects are not significant.
Sexual adverse effects occur at the rate of 2.1 to 3.8%. This was found to be comparable to placebo. (A placebo is a substance used in medical studies that do not have any active ingredients and is not expected to have any physiological effect. This is used as a control or a comparison when doing studies.)

The literature review also considered the stance of the position of the FDA (Food and Drug Administration) presumably because they were the body that was responsible for the authorisation of use of Finasteride in America where it was first used. The Food and Drug Administration (FDA) recently reviewed 421 post-marketing reports of sexual dysfunction with the use of finasteride 1 mg submitted to the agency’s adverse events reporting system database between 1998 and 2011.
They found that most of these side effects returned to normal within three months of discontinuing the drug.
It also went on to discuss the changes in labelling brought in. On April 11, 2012, the U.S. FDA announced changes to the professional labels for Propecia (finasteride 1 mg) to include libido disorders, ejaculation disorders and orgasm disorders that continued after discontinuation of the drug. They also added a description of reports of male infertility and/or poor semen quality that normalized or improved after drug discontinuation. Although these are not established, they are included in labels to make patients and doctors aware of the side effect profile. The FDA states that there is no clear cause and effect relationship between finasteride and the sexual adverse events that continued after stopping the drug.

Are the side effects of Finasteride reversible?

The literature review cites sexual problems as the most common side effect and tends to occur during the first year of treatment. Erectile dysfunction is the most common side effect followed by ejaculatory dysfunction and loss of libido. According to the review, these effects occurred early in therapy and returned to normal on stopping the drug or while continuing use of the drug over a period of time. It is interesting to note that these particular side effects could also resolve whilst still remaining on treatment and also mirrors the information from the trials made available from the manufacturers of Finasteride.
There are a few studies, however, suggesting that some patients receiving finasteride may develop sexual side effects which may not be entirely reversible. The literature review raises concerns about those studies with regards to the small sample sizes of those studies, bias in the selection
process and the lack of attention to study design. The authors of the literature review state that they did not receive any financial support or sponsorship therefore to all intents and purposes this appeared to be an unbiased review of the information available on Finasteride. The association between Finasteride and irreversible side effects is an area that would require further rigorous research to be able to come to any definitive conclusions.

When considering data, it is essential to be able to put it all into context. On the one hand, it would be unwise to simply discredit or ignore reports of side effects associated with Finasteride use. A useful way to approach looking at the data would be to try to put into the context of what is being said about Finasteride within the wider picture that we have with regards to its use. Finasteride has been around for some time and has been widely used in this time. It is known to be well tolerated and effective and although it does carry risks of side effects, these are known to occur relatively infrequently.

Ever heard of the nocebo effect?

There is also the interesting question of the nocebo effect. An article in the New York Times explores the notion that the anticipation of a possible side effect causes the side effect to be present even if the medication administered has no active ingredient. It is rather like the opposite of
the placebo effect. The placebo effect is when the placebo (medicine with no active ingredient or fake medication) used in medical trials causes a positive effect in the participants in the trial. The placebo effect occurs as a result of the patient’s expectation that the treatment will help even though they are getting a fake equivalent. The nocebo effect is the opposite of this. The patient expects the side effect and therefore experiences it even if what they are receiving is a fake equivalent (placebo). The article highlights a remarkable case in which a participant in an antidepressant drug trial was given placebo tablets and then swallowed 26 of them in a suicide attempt. Even though the tablets were harmless, the participant’s blood pressure dropped perilously low. The article also featured the use of finasteride administered to men to relieve symptoms of prostate enlargement. Half of the patients were told that the drug could cause erectile dysfunction, while the other half were not informed of this possible side effect. In the informed group, 44% of the participants reported that they experienced erectile dysfunction; in the uninformed group, that figure was only 15%!

How can I know if I will be affected?

All medicines are capable of causing side effects. However, that does not mean that it will happen to all patients and it does not mean that it will happen to you. Even if a side effect is described as common, this still means that the majority of people (approximately over 90% of people) taking the drug will not experience it. If a side effect is listed as uncommon, over 99% of people will not be affected. When you read about side effects. it gives you an idea of how likely it is to occur in a group of people but it doesn’t tell you whether you will go on to develop this side effect yourself.
Data is gathered continuously over the lifespan of the medication in use. For Finasteride, this would equate to just over 2 decades of use. All of this information is then compiled and presented to users in this big long list of possible effects that could happen. The long list of side effects that you see is a result of compilation of data and represents a list of possibilities which they should be interpreted in the context of probability.

What should I do if I think I have developed a side effect from Finasteride?

The first thing to do is to seek prompt medical advice from a doctor or a pharmacist. They can advise you on the next steps to take. You can also report side effects through the Yellow Card Scheme. There is also now a free app available. The Yellow Card Scheme helps the Medicines and Healthcare products Regulatory Agency gather data on medicines and the information provided is used to monitor safety. Finasteride is known to be an effective treatment option for androgenetic alopecia. It has an excellent safety profile and side effects are known to be rare and one the whole reversible. There is always a risk of possible side effects when taking any medication and a considered decision is the best approach to balancing the risk versus the benefit you would obtain from using Finasteride.


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  1. Weill Cornell Medical College. Julianne Imperato-McGinley. Professor of Medicine. Available at:
  2. Electronic Medicines Compendium 2018 Propecia 1mg tablet – Summary of Product Characteristics (SmPC) [online] [Accessed October 2018]
  3. Mysore, V., Shashikumar, B. and M. (2016) Guidelines on the use of finasteride in androgenetic alopecia. 82(2), 128-134
  4. Enck P, Hauser W 2012. Beware the Nocebo Effect. The New York Times [online] Available at: [Accessed October 2018]
  5. Clinical Knowledge Summaries 2018 [online] [Accessed October 2018]
  6. Medicines and Healthcare products Regulatory Agency 2009 MHRA Public Assessment Report The risk of male breast cancer with finasteride [online] [Accessed October 2018]

Mens Pharmacy is not liable for the currency or accuracy of the information contained in this blog post. For specific information about your personal medical condition, please contact our doctors or pharmacists for advice on [email protected].