What are the side effects of Finasteride?
- How common finasteride side effects actually are
- Sexual and mental health side effects explained
- What Post-Finasteride Syndrome is and what the evidence shows
- How 1 mg and 5 mg doses compare
- What to do if you experience side effects
- How common are finasteride side effects?
- What are the sexual side effects of finasteride?
- What are the mental health side effects of finasteride?
- What is Post-Finasteride Syndrome?
- How do finasteride 1mg and 5mg side effects compare?
- What are the side effects of topical finasteride?
- How can you reduce finasteride side effects?
- Do side effects resolve after stopping finasteride?
- When should you stop finasteride and seek medical advice?
- Final thoughts
How common are finasteride side effects?
The PLESS trial, a four-year placebo-controlled study of finasteride 5 mg in men with BPH, found sexual side effects in approximately 3-8% of men on finasteride compared to 2-4% on placebo. For finasteride 1 mg (used for hair loss), the incidence is slightly lower, consistent with the lower dose.
Good to know
Side effect rates in clinical trials may underrepresent real-world experience. The MHRA continues to monitor finasteride through post-marketing surveillance and the Yellow Card scheme.
What are the sexual side effects of finasteride?
Sexual side effects are the most commonly reported concern. The finasteride Summary of Product Characteristics at medicines.org.uk lists:
- Decreased libido: Approximately 1-2% at the 1 mg dose
- Erectile dysfunction: Approximately 1-2% at the 1 mg dose
- Ejaculation disorders: Less than 1% at the 1 mg dose
Finasteride reduces dihydrotestosterone (DHT), a hormone derived from testosterone that plays a role in sexual function. For most men who experience these effects, they resolve after stopping the medication.
What are the mental health side effects of finasteride?
The MHRA updated finasteride's product label following a review of post-marketing data to include depression, anxiety, mood changes, and suicidal ideation (rare) as uncommon side effects.
Warning!
If you experience low mood, depression, anxiety, or any thoughts of self-harm while taking finasteride, stop the medication and contact your GP or call 111 immediately.
What is Post-Finasteride Syndrome?
Post-Finasteride Syndrome (PFS) refers to persistent sexual, neurological, and psychological symptoms reported by some men after stopping finasteride, including erectile dysfunction, loss of libido, depression, and cognitive changes continuing after the drug has cleared the body.
PFS is not currently recognised as a formal medical condition by the MHRA, and its biological mechanism is not established. However, the MHRA has received Yellow Card reports consistent with persistent side effects and has acknowledged that sexual dysfunction may persist in a small number of men after stopping treatment.
Good to know
If you experience persistent symptoms after stopping finasteride, report them via the Yellow Card scheme at yellowcard.mhra.gov.uk and discuss them with your GP.
How do finasteride 1mg and 5mg side effects compare?
| Side effect | Finasteride 1 mg | Finasteride 5 mg |
|---|---|---|
| Decreased libido | Approx. 1–2% | Approx. 3–6% |
| Erectile dysfunction | Approx. 1–2% | Approx. 5–8% |
| Ejaculation disorders | Less than 1% | Approx. 3–4% |
| Depression/mood changes | Uncommon | Uncommon |
Source: Finasteride 1 mg and 5 mg Summaries of Product Characteristics, medicines.org.uk.
What are the side effects of topical finasteride?
Topical finasteride, applied directly to the scalp, produces lower systemic absorption than oral tablets. Early studies suggest it reduces scalp DHT effectively while causing a smaller reduction in serum DHT, which may translate to fewer systemic side effects. However, the evidence base is still developing and long-term safety data is limited. Topical finasteride is not currently licensed by the MHRA as a standalone product in the UK.
How can you reduce finasteride side effects?
- Start at the lowest effective dose; 1 mg is standard for hair loss
- Monitor early and maintain regular contact with your prescriber in the first few months
- Do not persist with significant side effects in silence; inform your prescriber promptly
- Consider topical formulations if systemic side effects are a concern, noting the limited evidence base
Do side effects resolve after stopping finasteride?
For the majority of men, sexual side effects resolve within weeks of stopping. Serum DHT typically returns to baseline within two weeks. For a small minority, symptoms persist beyond the expected washout period. If symptoms do not resolve within a few weeks of stopping, seek clinical assessment rather than expecting further spontaneous resolution.
When should you stop finasteride and seek medical advice?
Stop finasteride and contact your GP promptly if you experience significant sexual dysfunction that is distressing, depressive symptoms or mood changes, any thoughts of self-harm, or signs of an allergic reaction.
Final thoughts
Finasteride is effective for hair loss and BPH, and for most men side effects are uncommon and reversible. For a minority they are significant, and this deserves acknowledgement rather than dismissal. Starting at the lowest effective dose, monitoring early, and staying in contact with your prescriber are the most practical steps to using finasteride safely.
DoktorABC connects UK patients with licensed prescribers who can assess suitability for finasteride and provide ongoing clinical guidance.
FAQ
Are finasteride side effects common?
In clinical trials, sexual side effects occurred in approximately 3 to 8% of men on 5 mg and somewhat less on 1 mg. Most men do not experience significant side effects.
Are finasteride side effects reversible?
For most men, yes. Sexual side effects typically resolve after stopping. A small minority report persistent symptoms beyond the expected washout period.
How long do finasteride side effects last?
Most resolve within weeks of stopping. If symptoms persist beyond a month after discontinuation, seek medical assessment.
What is Post-Finasteride Syndrome?
A contested condition describing persistent symptoms after stopping finasteride. Not formally recognised by the MHRA, but persistent side effects have been reported and should be investigated clinically.
Can finasteride cause depression?
The MHRA updated finasteride's label to include depression and suicidal ideation as uncommon side effects. Contact your GP promptly if you experience mood changes.
Is topical finasteride safer than oral?
Early evidence suggests lower systemic absorption and potentially fewer systemic side effects, but the evidence base is still developing.
Where can I report a finasteride side effect?
Via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk, through the Yellow Card app, or by asking your prescriber or pharmacist to report on your behalf.
The DoktorABC medical advisory board
Dr. Roland Ruiken
Medical advisor, Norway
Dr. Viktor Simunovic
Medical advisor, Croatia