There are certain side effects associated with the use of Propecia, just as there are with any medication.

In some cases, these side effects will either go away on their own after a short time, or cease when treatment is halted. However, you should still notify your doctor if you notice anything unusual.

Seek medical advice immediately if you have any side effects that might be an indicator of an allergic reaction, such as swelling of the throat, face or lips, problems swallowing or breathing, hives or an itchy rash when taking finasteride.

It is also important to tell your doctor right away if you become depressed, or if you notice any abnormalities in your breast tissue including pain, lumps, enlargement or discharge from the nipples.

On this page, we’ll discuss some of the secondary effects associated with Propecia, and how common they are.

Clinical trials

Propecia was tested  in three placebo-controlled, double blind, multicentre studies over 12 months, involving a total of more than 3,200 participants. It was concluded that Propecia had a similar safety profile to that of a placebo.

Treatment was stopped due to ‘clinical adverse experience’ in:

  • 1.7% of 945 men taking Propecia
  • and 2.1% of 934 men taking the placebo.

Sexual desire and sexual function

The patient information leaflet for Propecia treatment lists several possible side effects of a sexual nature.

The following side effects are listed as ‘uncommon’ (affecting up to 1 in 100 people):

  • Impotence (erectile dysfunction);
  • decreased libido;
  • or ejaculatory problems such as a smaller amount of semen.

It also lists other potential side effects of a sexual nature, however the frequency of these is listed as unknown. These include:

  • persistent problems obtaining an erection after ending treatment;
  • persistent lowered libido after ending treatment;
  • and persistent ejaculatory problems after ending treatment.

Data on side effects of a sexual nature was collected in clinical trials and reported as follows:

Side effect

Propecia - % of men who reported side effect

Placebo - % of men who reported side effect

Decreased libido



Erectile dysfunction



Decreased volume of ejaculate



In the first 12 months of the trial, side effects of a sexual nature related to the treatment were noted in 3.8% of the treatment group, and 2.1% of the placebo group.

In the treatment group, the incidence of these fell as the trial went on, to 0.6% over the next four years.

The SPC states that men who discontinued use of Propecia found these secondary effects to resolve. The effects also resolved for many of the participants that continued with the trial.

However, sexual dysfunction problems which persist after stopping Propecia treatment, including lower libido and erectile dysfunction, have been reported in postmarketing use.


Male infertility or problems with sperm quality are listed under the ‘unknown frequency’ section of Propecia side effects.

The clinical trials carried out did not produce information on this subject. Any males that were planning to father a child were removed from the clinical trials. The animal studies did not produce statistically significant information about the drug’s effect on fertility.

Reports of infertility have since been received following the release of the product on the market. The SPC states that some of those who reported infertility as a side effect had other potential risk factors, thus making it is difficult to pinpoint causality.

It is possible for men who take Propecia to experience problems with their fertility. The quality or numbers of sperm seen in the semen may change during a course of Propecia. However, the information provided in the SPC also states that the quality of the sperm is reported to return to normal following discontinuation.

Studies into the potential long-term impact on male fertility have not been carried out.

Breast cancer

The patient information guide instructs those who use Propecia to immediately report any changes to their breast tissue to their doctor. This includes any lumps, nipple discharge, enlargement of the breast tissue, tenderness or pain.

It has not been possible to calculate the prevalence of breast cancer. Information on this secondary effect was received from individual reports following release.  

Mood alterations

The patient information leaflet warns patients to discontinue their use of Propecia and speak to their doctor if they notice any symptoms of depression. Instances of depression, changes in mood and suicidal thoughts have been received by the manufacturer via post-marketing reports.

The SPC states that cases of depression are uncommon. It also notes that in phase III clinical trials, the incidence of depression in Propecia users was no different to placebo.

Yellow card scheme

If you experience side effects when using any type of medication you can report them through the Yellow Card Scheme. This scheme helps the MHRA to check and update the safety information relating to medicines in the UK. The information received from patients is used to pinpoint any issues and address them when necessary.

Page last reviewed:  25/09/2017