Finasteride Side Effects — UK Patient Guide
Information sourced from the MHRA-approved Propecia Summary of Product Characteristics (SmPC) and the electronic Medicines Compendium (eMC). Reviewed by our medical board. | Back to UK hub
Most men who take finasteride tolerate it well. The most commonly reported side effects affect sexual function in a minority of users; the majority of these resolve spontaneously on continued treatment or after stopping.
Side effects by MHRA frequency category
The MHRA-approved SmPC for Propecia (finasteride 1 mg) uses standard EU/EEA frequency categories:
| Category | Definition | Reported side effects |
|---|---|---|
| Common | ≥1/100, <1/10 (affects up to 1 in 10) | Decreased libido, erectile dysfunction, ejaculation disorders (ejaculatory dysfunction, decreased volume) |
| Uncommon | ≥1/1,000, <1/100 (affects up to 1 in 100) | Breast tenderness or enlargement (gynaecomastia), depression, anxiety, hypersensitivity reactions (swelling of lips/face/throat) |
| Rare | ≥1/10,000, <1/1,000 | Testicular pain, palpitations |
| Not known | Cannot be estimated from available data | Persistent sexual dysfunction after stopping (see below); suicidal ideation |
Sexual side effects — what the evidence shows
In pivotal 2-year placebo-controlled trials (Kaufman 1998), the rate of sexual adverse effects on finasteride 1 mg was low:
| Side effect | Finasteride 1 mg | Placebo |
|---|---|---|
| Decreased libido | 1.8% | 1.3% |
| Erectile dysfunction | 1.3% | 0.7% |
| Ejaculation disorders | 1.2% | 0.7% |
Resolution rates were high: in men who discontinued finasteride, sexual function returned to baseline in the majority within 3–12 months.
Post-finasteride syndrome (PFS)
MHRA position (2020): The MHRA updated the Propecia SmPC in 2020 to include persistent sexual dysfunction (persisting after discontinuation of finasteride) in the “Not known” frequency category following signal review. The label now also includes suicidal ideation. These are rare events but the MHRA considers the benefit/risk balance to remain positive for the licensed indications.
Post-finasteride syndrome (PFS) is a term used to describe a constellation of persistent sexual, neurological, and physical symptoms that some patients report after stopping finasteride. The estimated prevalence remains uncertain (studies range from very rare to a few percent), and a clear biological mechanism has not been established. If you experience symptoms you believe are related to finasteride, discuss with your GP or dermatologist.
Mood and mental health — UK warnings
The MHRA added a Black Triangle (▼) warning to Propecia in 2017, requiring enhanced pharmacovigilance. Depression and anxiety are listed as uncommon side effects. The 2020 label update added suicidal ideation to the SmPC.
If you experience low mood, anxiety, or thoughts of self-harm while taking finasteride:
- Contact your GP promptly
- Call Samaritans on 116 123 (free, 24/7)
- Report the reaction to the MHRA Yellow Card scheme (see below)
Reporting side effects: MHRA Yellow Card
UK patients and healthcare professionals can report suspected adverse reactions from finasteride directly to the MHRA via the Yellow Card scheme:
- Online: yellowcard.mhra.gov.uk
- By phone: 0800 731 6789 (freephone, Mon–Fri 9am–5pm)
- Via the Yellow Card app (iOS/Android)
Yellow Card reports from UK patients directly contribute to MHRA signal detection and label updates. They are taken seriously and do not require certainty that the drug caused the reaction.
Prostate-specific antigen (PSA) and finasteride
Finasteride reduces serum PSA by approximately 41% after 6+ months at 1 mg/day. UK GPs and urologists monitoring PSA in men on finasteride must apply a correction factor. See the PSA section on our UK hub for the correction formula.
Frequently asked questions
Do finasteride side effects go away?
For most men, side effects are temporary. In placebo-controlled trials, sexual side effects resolved in the majority of men who continued treatment and in virtually all men who stopped. Persistent side effects after stopping are documented but appear to be uncommon based on available data.
Can I get a Yellow Card report from my GP?
Yes. Your GP can submit a Yellow Card report on your behalf, or you can submit one yourself at yellowcard.mhra.gov.uk. You do not need a GP’s approval to submit your own report.
Is finasteride safe long-term in the UK?
Long-term safety data (up to 10 years) from the PCPT trial and extensions of the AGA pivotal trials suggest no new safety signals emerge with continued use. The MHRA benefit/risk assessment for licensed indications remains positive. See our long-term safety guide for the full evidence.
Sources: MHRA Propecia SmPC (eMC, 2024). Kaufman KD et al. JAAD 1998;39(4):578–589. MHRA Drug Safety Update: Finasteride persistent sexual dysfunction (2020). NICE CKS: Alopecia (2023).
Related: UK homepage | Full side effects guide (US) | Post-finasteride syndrome | Long-term safety