Finasteride Side Effects: What to Expect

Finasteride is the most widely used oral treatment for male pattern hair loss in the UK, and its side effects are among the most searched topics in men's health. If you've been prescribed finasteride or you're considering taking it, this guide covers what the clinical evidence actually says about finasteride side effects, how often they occur, and what you can do if you experience them.

What Is Finasteride?

Finasteride 1mg is a prescription medication licensed for the treatment of androgenetic alopecia (male pattern baldness) in men.²

Finasteride works by inhibiting 5-alpha reductase, the enzyme that converts testosterone into dihydrotestosterone (DHT). DHT is the androgen responsible for progressive miniaturisation (gradual shrinking) of hair follicles in men with a genetic predisposition to hair loss. By reducing DHT levels by approximately 60 to 70% with daily use, finasteride slows hair loss and, in many men, promotes partial regrowth.⁴

Finasteride Side Effects and How Often They Occur

Because DHT also plays a role in sexual function, reducing it can occasionally affect libido, erections, or ejaculatory function. This is understandably one of finasteride's most commonly searched for concerns around potential side effects.

The most frequently cited finasteride side effects in large-scale clinical trials include:

• Reduced libido – reported in around 1.8% of men in clinical trials
• Erectile dysfunction – reported in approximately 1.3% of men in clinical trials
• Reduced ejaculate volume – reported in around 1.2% of men in clinical trials
• Breast tenderness or enlargement (gynaecomastia) – classified as uncommon in the official prescribing information (fewer than 1 in 100 but more than 1 in 1,000 users)

These figures come from the original placebo-controlled registration trials.⁴ Notably, men in the placebo groups reported sexual side effects at rates approaching 1%, which highlights how difficult it can be to attribute symptoms definitively to the medication rather than background rates in the general population.

The official prescribing information classifies individual sexual side effects as “common” (affecting between 1 in 100 and 1 in 10 users), reflecting absolute rates of around 1 to 2%.² To put those numbers in perspective: in the same trials, men taking placebo reported sexual side effects at a combined rate of 2.1%, versus 3.8% for finasteride. The majority of men taking finasteride for hair loss do not experience them.

Depression and mood changes are also listed in the finasteride product information, following a 2019 MHRA Drug Safety Update.⁵ The frequency is classified as “not known”, meaning it cannot be reliably estimated from the available clinical trial data. Reports have come primarily from longer-term monitoring rather than the original placebo-controlled trials. If you notice a significant change in your mood after starting finasteride, particularly low mood or feelings of depression that weren't present before, speak to your GP.

Do Finasteride Side Effects Go Away?

For most men, yes. In the pivotal clinical trials, sexual side effects resolved in men who stopped taking finasteride.⁴ The official prescribing information also notes that in some men who continued taking the drug, side effects resolved spontaneously over time without any change to their regimen.²

A smaller number of men report that sexual symptoms persist after stopping finasteride. This has been labelled post-finasteride syndrome in some literature, though its mechanisms are not fully understood and the evidence base is still limited.⁶

The MHRA has acknowledged rare reports of persistent effects following discontinuation.⁵ If you have specific concerns about long-term risk, discussing your personal health history with a GP before starting is a sensible step.

Are Finasteride Side Effects Permanent?

The available clinical evidence does not support the idea that finasteride side effects are permanent for the vast majority of users.⁶ Regulatory bodies including the MHRA note that reports of persistent effects exist, but emphasise that these cases are uncommon and that causality is not always straightforward to establish given the background prevalence of sexual dysfunction in the general male population.⁵

One further consideration – finasteride reduces prostate-specific antigen (PSA) levels by approximately 50%.³ This isn't harmful in itself, but it is clinically relevant for men being monitored for prostate conditions. Any clinician reviewing your PSA should be aware you're taking finasteride, as the result will need to be interpreted accordingly.

Finasteride Side Effects: Topical vs Oral

Topical finasteride, applied directly to the scalp rather than taken as a tablet, is used because it achieves lower systemic absorption. Because less of the drug enters the bloodstream, DHT suppression is more localised to the scalp, which in theory reduces hormonal effects throughout the rest of the body.⁶

Smaller studies suggest topical formulations produce a lower incidence of sexual side effects compared to oral tablets, though the evidence base is less extensive than that for the 1mg oral dose.⁶ Topical finasteride may be worth discussing with your prescriber if sexual side effects are a specific concern.

Taking Finasteride With Minoxidil: Does It Increase Side Effects?

Using finasteride and minoxidil together is a well-established combination for male pattern hair loss, and most clinical guidance for androgenetic alopecia acknowledges it as an effective approach.¹

The two medications work via entirely different mechanisms. Finasteride reduces DHT, while minoxidil stimulates blood flow to follicles, and they don't interact with each other or compound one another's side effect profiles.

Minoxidil's own side effects (scalp irritation, unwanted facial or body hair growth at higher doses) are entirely separate from finasteride's hormonal effects. The combination is generally well tolerated by most patients too.

How to Reduce the Risk of Finasteride Side Effects

If you're starting finasteride and want to minimise your risk, these steps are worth considering:

• Take the standard licensed dose. Finasteride 1mg is the approved dose for hair loss. There's no clinical benefit to a higher dose for the treatment of hair loss and there's a greater risk of side effects as well.²
• Allow time before reassessing. Some men experience mild initial symptoms that resolve within a few weeks as the body adjusts. You should avoid making a final judgement based on the first two to four weeks, as symptoms can ease over time.
• Track your symptoms carefully. Keeping note of when symptoms started relative to when you began finasteride helps you and your clinician assess causality accurately. Many sexual symptoms have unrelated causes.
• Speak to your prescriber before stopping. If side effects are persistent or affecting your quality of life, contact the clinician who prescribed your medication. Don't stop taking the medication abruptly without guidance from a medical professional.
• Establish a baseline. Erectile dysfunction and reduced libido are fairly common in the general male population, particularly with age or stress. A clear picture of your baseline before starting makes it much easier to interpret any changes.

When to Seek Further Advice

Contact your prescribing clinician or GP if:

• Sexual side effects are persistent (lasting more than a few weeks)
• Symptoms are significantly affecting your wellbeing or relationships
• You notice breast tenderness, pain, or enlargement
• You experience significant mood changes, low mood, or depression you weren't experiencing before starting finasteride
• You experience a skin rash, swelling, or any signs of an allergic reaction
• You're taking other prescription medications and haven't checked for interactions

A full list of known side effects and drug interactions for finasteride is available in the patient information leaflet.

References

1. NHS. Hair loss. Available at: https://www.nhs.uk/conditions/hair-loss/
2. Electronic Medicines Compendium (eMC). Finasteride 1mg Film-Coated Tablets. Available at: https://www.medicines.org.uk/emc/
3. British National Formulary (BNF). Finasteride. Available at: https://bnf.nice.org.uk/drugs/finasteride/
4. Kaufman KD, Olsen EA, Whiting D, et al. Finasteride in the treatment of men with androgenetic alopecia. Journal of the American Academy of Dermatology. 1998;39(4):578–589.
5. Medicines and Healthcare products Regulatory Agency (MHRA). Finasteride 1mg: rare reports of persistent sexual side effects after discontinuation. Drug Safety Update. 2019.
6. Gupta AK, Venkataraman M, Talukder M, Bamimore MA. Finasteride for hair loss: a systematic review. Journal of Dermatological Treatment. 2022;33(3):1367–1378.

This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.

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