Propecia side effects: How common are they?

DoktorABC editorial team

Accurate, up-to-date health information written by our editorial team and reviewed by UK-registered prescribers.

How common are Propecia side effects?

In the pivotal clinical trials submitted for MHRA licensing, sexual side effects were the most commonly reported adverse events, occurring in approximately 3.8% of men on Propecia compared to 2.1% on placebo. To put that in context, the large majority of men in both groups reported no sexual side effects at all. 

What are the sexual side effects of Propecia?

The three primary sexual side effects listed in the Propecia Summary of Product Characteristics at www.medicines.org.uk are:

• Decreased libido: Approximately 1.8% on Propecia versus 1.3% on placebo
• Erectile dysfunction: Approximately 1.3% versus 0.7% on placebo
• Ejaculation disorders: Approximately 1.2% versus 0.7% on placebo

For most men who experience these effects, they resolve after stopping the medication.

What are the mental health side effects of Propecia?

Following a review of post-marketing data, the MHRA updated Propecia's product label to include:

• Depression
• Anxiety
• Mood changes
• Suicidal ideation (rare)

These are classified as uncommon, affecting fewer than 1 in 100 people.

Are there any serious rare side effects?

The Propecia label lists male breast cancer as a very rare adverse event. A causal relationship has not been definitively established, but any breast lump, breast pain, or nipple discharge while taking Propecia should be investigated promptly by a GP.

Signs of an allergic reaction, including facial swelling or difficulty breathing, require emergency medical attention immediately.

Are Propecia side effects permanent?

For most men, side effects resolve after stopping. The Propecia SmPC states that resolution occurred in all men who discontinued due to sexual side effects in clinical trials.

A minority of men report symptoms that persist after stopping, associated with what is sometimes called Post-Finasteride Syndrome (PFS). PFS is not currently recognised as a formal medical condition by the MHRA, but the agency has acknowledged via Yellow Card data that persistent sexual dysfunction after stopping has been reported.

Do Propecia and generic finasteride have different side effects?

No. Both contain the same active ingredient at the same dose, and the side effect profile is clinically identical. Some patients report subjective differences after switching between branded and generic versions, but these are not supported by pharmacological evidence.

What should you do if you experience Propecia side effects?

• Sexual side effects: Speak to your prescriber before stopping. They can advise on whether to continue, adjust your approach, or consider an alternative.
• Mental health effects: Stop immediately and contact your GP or call 111.
• Persistent symptoms after stopping: Seek clinical assessment and report to the MHRA Yellow Card scheme.
• Breast changes or allergic reactions: Seek prompt or emergency medical attention as appropriate.

DoktorABC connects UK patients with licensed prescribers who can assess and support men experiencing side effects from Propecia.

Final thoughts

Propecia's side effect profile is well characterised, and for most men significant side effects do not occur. The absolute difference in sexual side effect incidence between Propecia and placebo in clinical trials is modest, though real-world experience suggests some men are more affected than trial data alone implies. If you have concerns about side effects, the right step is always a conversation with your prescriber rather than stopping treatment without guidance.

FAQ

The DoktorABC medical advisory board

Dr. Roland Ruiken

Medical advisor, Norway

Dr. Viktor Simunovic

Medical advisor, Croatia

To the medical advisory board