Finasteride's side effects: how common are they, what fades, and what does your doctor need to know?

In the first year, 3.8% of those taking finasteride and 2.1% of those on placebo reported a sexual side effect attributed to the drug. This is the pooled data from three 12-month, placebo-controlled, double-blind studies: 945 men took 1 mg finasteride daily, 934 took a placebo, all men aged 18 to 41 with male pattern hair loss.2 The difference between the two, roughly 1.7 percentage points, is what can be attributed to the drug; without the placebo arm, the 3.8% figure alone would be misleading.

In detail, according to the summary of product characteristics (the authority-approved medicine description for doctors): decreased libido was reported by 1.8% of those taking finasteride and 1.3% on placebo, erectile dysfunction by 1.3% and 0.7%, reduced ejaculate volume by 0.8% and 0.4%. Ejaculate volume was also directly measured in a separate study, and there it showed no difference from placebo.1

The complaint became less common over time: over the following four years it fell to 0.6% among those taking finasteride, and by year five every item had fallen below 0.3%. Those who stopped taking it saw the complaint resolve, and so did many who continued. Because of the sexual complaint, around 1% on both arms stopped in the first year; because of any adverse event at all, 1.7% of those taking finasteride and 2.1% of those on placebo.1

What you can take from this: in the first year, 1.7 percentage points more people taking the drug reported a sexual complaint than on placebo, and in the studies this rate fell in the following years.

The 1 mg finasteride summary of product characteristics sorts side effects into two tiers. Decreased libido, erectile dysfunction, ejaculation disorder and depression are "uncommon", which on the label's scale means it affects 1 to 10 people in 1,000; for the sexual items this is the excess over placebo at month 12.1

The frequency of the remaining items is "not known": anxiety, suicidal ideation, breast tenderness and enlargement, testicular pain, blood in the semen, infertility, hypersensitivity reactions (rash, itching, hives, swelling), palpitations, and raised liver enzymes. "Not known" means the frequency can't be estimated from the data, because these items come from voluntary reports made after the product went on the market; it doesn't mean rare, and it doesn't mean common either. For depression, the label separately notes that its frequency in the controlled studies didn't differ from placebo, and the classification comes from post-marketing reports.1 A 2023 letter published in a urology journal, however, summarised that most of the current evidence from the dermatology literature suggests depressive symptoms are more common in those taking a 5-alpha-reductase inhibitor; the authors didn't consider the causal link with suicidal ideation to be settled.6 For suicidal ideation, the causal link was confirmed by the EU-wide assessment in 2025, see below.10

I'm quoting the data from the label of the 1 mg daily tablet approved for hair loss. The 5 mg finasteride is for prostate enlargement, for older men, so its data concerns a different dose and a different age group; where 5 mg data appears in the article, I mark it separately.2 What you can take from this: with any side-effect list, check which dose's label it's from, and whether the item is next to a number, or to "not known".

Yes, it now appears on both the American and the European medicines authority's label. On the American label's post-marketing list, depression already appeared in the 2010 version;9 the July 2022 revision added suicidal ideation and behaviour alongside it.2 In Europe, on 19 June 2025 the member states' Coordination Group for Mutual Recognition and Decentralised Procedures (CMDh) approved the measures of the European Medicines Agency's safety committee (PRAC). Following an EU-wide review, PRAC confirmed that suicidal ideation is a side effect of the 1 mg and 5 mg finasteride tablet; its frequency can't be estimated from the available data, and most cases were reported in those taking the 1 mg tablet.3

The review found 325 cases in the European side-effect database, 313 for finasteride and 13 for dutasteride (one case reported both), against an estimated exposure of roughly 270 million and 82 million patient-years respectively; a patient-year is how many people took it for how many years, added together. Most of the cases occurred in patients treated for hair loss. This figure isn't a frequency: the data comes from voluntary reports, which is why the authority states the frequency can't be estimated.13 At the same time, PRAC concluded that the benefit of finasteride and dutasteride still outweighs the risk for every approved use.3 For dutasteride, the link couldn't be confirmed, but because it works the same way, the warning was added to its label too, as a precaution. For the finasteride spray applied to the scalp, the review found no link.3

According to the 1 mg tablet's label, patients should be monitored for psychiatric symptoms; if they occur, treatment should be stopped and a doctor consulted. The label also states that sexual dysfunction may, in some people, contribute to mood changes, and that the box contains a patient card as a reminder of this.1 The authors of a 2023 letter published in a urology journal state that, in the absence of comprehensive randomised trials, the causal link isn't settled, and recommend mental health screening for everyone starting finasteride.6 Later, in its 2025 EU-wide assessment report, PRAC confirmed the causal link between oral finasteride and suicidal ideation, and, for the 1 mg tablet, judged the benefit-risk balance to remain favourable together with the new measures.10 In the body that approved the decision (CMDh), the representatives of Belgium and France recorded a dissenting opinion: in their view, the balance for 1 mg finasteride in hair loss is negative.11 I've written more about this in the article on post-finasteride syndrome.

What you can take from this: if you feel low or have suicidal thoughts while taking it, the label states that you should stop and see a doctor; if it feels urgent, don't wait for your next appointment.

In the 1 mg studies, breast tenderness and enlargement weren't more common than on placebo.2 Based on post-marketing reports, however, the 1 mg label lists it, with a "not known" frequency.1 A numerical difference comes from the 5 mg study in older men treated for prostate enlargement: in years 2 to 4, breast enlargement occurred in 1.8% of those taking finasteride versus 1.1% on placebo, and breast tenderness in 0.7% versus 0.3%.2 That's a fivefold dose and a different age group, so it can't be carried over to the 1 mg dose.

The label also states that breast cancer has been reported post-marketing in men taking 1 mg finasteride, and that doctors should instruct patients to promptly report any change in breast tissue, such as lumps, pain, enlargement, or nipple discharge.1

What you can take from this: if you notice a lump, pain or enlargement in your breast, the label states that you should report it to your doctor immediately, even though this complaint wasn't more common than on placebo in the controlled study.

It doesn't lower it, it raised it slightly in the studies. Finasteride inhibits an enzyme called 5-alpha-reductase, which converts testosterone into DHT (dihydrotestosterone); DHT is the hormone that drives male pattern hair loss. When the conversion slows, less DHT is made, and the starting material, testosterone, builds up a little.

According to the American label, within 24 hours of a 1 mg tablet, blood DHT levels fall by 65%, while the average level of testosterone and oestradiol (an oestrogen that's also made in men) rises by roughly 15% from baseline, but stays within the normal physiological range.2 What you can take from this: finasteride lowers DHT, not testosterone.

Finasteride lowers your PSA value, so if you're going for a prostate screening, your doctor needs to know you take it. PSA (prostate-specific antigen) is a blood value also used in prostate cancer screening. In men aged 18 to 41 taking 1 mg daily for hair loss, the average fell from 0.7 to 0.5 ng/ml over 12 months; at the 5 mg dose, in older men treated for prostate enlargement, it fell by roughly 50%.2

According to the 1 mg label, doubling the PSA value should be considered while taking finasteride, before evaluating the result.1 The American label adds that any confirmed rise from the lowest measured value should be investigated, because it may indicate prostate cancer, even if the value is still within the normal range.2

What you can take from this: ask your doctor this if you're getting a PSA test: do they know you're taking finasteride, and will they adjust how they evaluate the result accordingly?

In a study of men with prostate enlargement taking 5 mg, the group that was informed reported a sexual side effect nearly three times more often, on the same medication. This phenomenon is called the nocebo effect: an unpleasant symptom that isn't a direct consequence of how the drug works. In a 2007 Italian study, 120 sexually active men with prostate enlargement took 5 mg finasteride daily for a year, described as "proven-effective compound X". One group was told the drug could cause erectile dysfunction, decreased libido and ejaculation problems, but that these weren't common; the other group wasn't told this.5

107 men completed the study. Of those who were informed (55 people), 43.6% reported at least one sexual side effect, versus 15.3% of those who weren't (52 people).5

The study was done at 5 mg, in men with prostate enlargement, with no placebo arm, both groups took finasteride. It shows how much information changes the rate of reported complaints; it doesn't show that the complaints aren't real. What you can take from this: it's always worth looking at side-effect figures alongside the placebo arm, because the placebo arm also captures the effect of expectation.

According to the summary of product characteristics, the complaint resolved in those who stopped taking it.1 Post-marketing, however, reports have also come in where sexual dysfunction (decreased libido, erectile and ejaculation disorder) persisted even after stopping; the American label also lists orgasm disorder.12 Neither label gives a figure for how common this is.

In the literature this is called post-finasteride syndrome (PFS): a cluster of sexual, neurological/psychiatric and physical complaints that persists for at least three months after stopping. A 2020 review states that the studies so far can neither confirm nor rule it out as a standalone condition.7 I didn't find a controlled study on it. What we know and what we don't, I've written up in the article on post-finasteride syndrome; what happens to your hair after stopping is in the article on stopping finasteride. Ask your doctor this: what should be done if the complaint persists after stopping.

According to the authors of the 2020 review, in anyone who has previously had depression, sexual dysfunction or a fertility problem, using a 5-alpha-reductase inhibitor should be weighed carefully and individually.7 From this and the above, these questions follow:

• Have I had depression, anxiety, or a sexual or fertility problem before, and what does that mean for this decision?
• What should I do if I notice a mood change or a sexual complaint?
• If I get a PSA test, how do we evaluate the result?
• Are we planning a child? I've written about this in a separate article: finasteride and planning a child.
• Could the scalp spray be an option? See: topical finasteride.

I've written about the tablet's basics, dutasteride, and where to get it in the article on oral DHT blockers.

Microneedling is a mechanical stimulus with no hormonal effect, so it can be used alongside medications that act on DHT. Dermastamp is a fixed 1 mm, at-home device: the needle stimulates the area around the follicle, and its mechanism doesn't touch DHT. This is inferred from the mechanism, not measured. You don't skip oral finasteride or dutasteride on the day of stamping. With scalp-applied products, the day of stamping is a pause, and the exact timing differs by product: the timing of actives. For anyone who'd rather not touch their hormones, this is a route that stays open, with one limitation: in the study measuring the combination, both groups also received minoxidil, and the study used a 1.5 mm clinical roller, not our fixed 1 mm device; there's less data for standalone use. What it can do, what it can't, and who it's not for: I've written it all on its page.

See Dermastamp