Is finasteride safe? What the trials and regulators say

Finasteride is a 5-alpha reductase inhibitor. It is prescribed at 5 mg for benign prostatic hyperplasia (BPH, an enlarged prostate) and at 1 mg for androgenetic alopecia (male pattern hair loss). This page sets out what the clinical trials, the product labels, the medicines regulators and the research on persistent symptoms say about its side effects. Those side effects are not only sexual: the labels and the research also cover mood, suicidal thoughts, thinking, and physical effects such as breast changes and semen quality. Whether to take it is a prescribing decision.

What the trials show

In the one-year clinical trials used for US approval, 36 of 945 men (3.8%) taking finasteride 1 mg reported at least one sexual side effect, compared with 20 of 934 men (2.1%) taking placebo. The label states that these effects resolved in men who stopped because of them, and in most men who kept taking the drug. The trials counted mainly sexual side effects; the label also records breast enlargement (0.5% vs 0.1%), breast tenderness (0.4% vs 0.1%) and rash (0.5% vs 0.2%) in the trials. Depression, anxiety and cognitive symptoms were not measured in these trials at all (Propecia prescribing information).

A 2019 meta-analysis of 15 placebo-controlled trials in 4,495 men with hair loss found a higher risk of sexual dysfunction with finasteride than with placebo (risk ratio 1.66, 95% CI 1.20–2.30) (Lee et al., 2019).

Expectation also affects what people report. In a study of 120 men taking finasteride 5 mg for BPH, men who were told in advance about possible sexual side effects reported them more often (43.6%) than men who were not told (15.3%) (Mondaini et al., 2007). This study used the prostate dose in older men and measured side effects during treatment only. It did not study whether symptoms persist after stopping, and it does not show that side effects on the 1 mg dose are imaginary.

Why the trials cannot settle persistence

A review of 34 finasteride hair-loss trial reports found that none had adequate safety reporting. In 76% of them, safety was followed for a year or less, and the pattern of results suggested that sexual side effects were under-detected (Belknap et al., 2015). The trials measured side effects while men were taking the drug. They did not follow men after they stopped.

What the regulators say

• United States. The Propecia label lists post-marketing reports of sexual dysfunction that continued after treatment was stopped, including erectile dysfunction, libido disorders, ejaculation disorders and orgasm disorders. It also lists depression, and suicidal ideation and behaviour. The label states that because these reports are voluntary, it is not always possible to estimate their frequency or to establish that the drug caused them (Propecia prescribing information).
• United Kingdom. The Medicines and Healthcare products Regulatory Agency (MHRA) states that finasteride is associated with depression, suicidal thoughts and sexual dysfunction "which may persist after treatment is stopped" (MHRA, 2026). Finasteride packs include a patient alert card. In 2024 the MHRA reported that almost half of 426 UK Yellow Card reports of sexual dysfunction were recorded as not recovered or not resolved (MHRA, 2024). The MHRA also notes that a report does not necessarily mean the medicine caused the reaction.
• European Union. In 2025 the European Medicines Agency (EMA) confirmed suicidal thoughts as a side effect of finasteride 1 mg and 5 mg tablets, with a frequency that cannot be estimated from the available data. It found no evidence linking suicidal thoughts to finasteride skin spray. It concluded that the benefits of finasteride still outweigh its risks for its approved uses. Packs of 1 mg tablets now include a patient card (EMA, 2025).

Mood, suicidal thoughts and thinking

The trials did not measure mood. What is known comes from later studies, each with limits.

• Irwig interviewed 61 former finasteride users whose sexual symptoms had persisted for at least three months and 29 men with hair loss who had never taken it. None had a psychiatric history before finasteride. Depressive symptoms were reported by 75% of the former users and 10% of the controls, and suicidal thoughts by 44% and 3% (Irwig, 2012, J Clin Psychiatry). The men were recruited because they already had persistent sexual symptoms, so the study shows how common mood symptoms were in that group, not how often finasteride causes them.
• A Harvard group compared men with persistent sexual symptoms after finasteride, men who had taken it without symptoms, and men who had never taken it. The symptomatic men had higher depression scores, more negative mood and more cognitive complaints, although their scores on objective cognitive tests were normal. Brain imaging showed abnormal responses in circuits linked to sexual arousal and depression. Hormone levels, androgen action in skin and the genes for the enzyme finasteride blocks did not differ between the groups, so the study found no evidence that the symptoms come from lasting androgen deficiency (Basaria et al., 2016). It was a small study and cannot say what the cause is.
• In a Canadian database study of 93,197 men aged 66 or older starting finasteride or dutasteride for an enlarged prostate, matched to men who did not, there was no increase in suicide (hazard ratio 0.88, 95% CI 0.53–1.45), but self-harm (HR 1.88) and new depression (HR 1.94) were higher in the first 18 months, and depression stayed somewhat higher afterwards (HR 1.22). The absolute increases were 17 and 237 events per 100,000 patient-years (Welk et al., 2017). These were older men on the prostate dose.
• In the World Health Organization's adverse-event database, reports of suicidality (reporting odds ratio 1.63) and psychological adverse events (ROR 4.33) were disproportionately linked to finasteride. The signal for suicidality was concentrated in men under 45 and in men taking it for hair loss, and was absent in older men taking it for the prostate. The authors say this could reflect younger men being more vulnerable, or more reporting after the issue became public in 2012, or both (Nguyen et al., 2021). Reports of this kind cannot give a rate.

A proposed explanation is that finasteride also lowers neuroactive steroids in the brain that affect mood and sexual function (Irwig, 2012, J Clin Psychiatry). In a pilot study of 16 men with post-finasteride symptoms and 20 controls, the gene for the type 2 enzyme finasteride blocks was more often switched off (methylated) in the men's cerebrospinal fluid, 56% vs 8%, but the authors could not say whether finasteride caused this or it was there before (Melcangi et al., 2019). These mechanisms are unproven.

Symptoms after stopping: what is known

Irwig and Kolukula interviewed 71 men aged 21–46 whose sexual symptoms had lasted at least three months after stopping finasteride. At interview, the symptoms had lasted 40 months on average (Irwig & Kolukula, 2011). When 54 men with persistent symptoms were re-assessed about 14 months later, 96% still reported them (Irwig, 2012). Chiriacò et al. described 79 young men who reported long-term effects after using finasteride for hair loss (Chiriacò et al., 2016), and Ganzer et al. surveyed men who reported persistent sexual, emotional and cognitive symptoms (Ganzer et al., 2015). All of these men were studied because they already had symptoms. These studies show that persistent symptoms occur. They cannot show how often.

In a US medical-records study, 34 of 4,284 men aged 16–42 who had taken finasteride at 1.25 mg a day or less (0.8%) had erectile dysfunction that lasted at least 90 days after stopping; the median duration was about four years (Kiguradze et al., 2017). The study had no comparison group of men who never took the drug, so it does not show how much of this finasteride caused.

A UK primary-care database study of 12,346 men with hair loss did not find a significant increase in recorded erectile dysfunction among men taking finasteride 1 mg (incidence rate ratio 1.03, 95% CI 0.73–1.44) (Hagberg et al., 2016). It counted only new diagnoses or treatment of erectile dysfunction recorded by doctors, which are likely to miss cases, and did not look at libido, mood or symptoms after stopping.

A 2026 study of 129 men with symptoms after stopping finasteride (for hair loss or an enlarged prostate) found that erectile function scores did not change over six months. Depression scores fell but did not return to normal in most of the men. The study had no comparison group (Jędrzejczyk et al., 2026).

Three questions are often mixed up: whether symptoms persist after stopping (persistence), whether finasteride caused them (causation), and whether they never go away (permanence). Persistence is described in the product labels and regulator warnings. Causation and permanence are not settled. "Post-finasteride syndrome" is the name used for symptoms that persist after stopping. A 2020 review describes them as sexual symptoms (low libido, erectile dysfunction, reduced arousal, difficulty reaching orgasm), depression, anxiety and cognitive complaints, and notes that the evidence rests mainly on patients' own reports, with few clinical studies (Diviccaro et al., 2020; the authors disclose funding from the Post-Finasteride Syndrome Foundation). Men also report physical symptoms such as genital numbness, and one small tissue study found differences in androgen-receptor density in the foreskin of 8 affected men compared with 11 controls (Di Loreto et al., 2014). Researchers disagree about the causes, and there is no established test or treatment for it.

Long-term users

Shin et al. reviewed 126 Korean men who stayed on finasteride 1 mg for at least five years. 108 (85.7%) improved, and 10 (7.9%) had sexual symptoms recorded in their notes. The authors say that studying only men who stayed on the drug for five years may overestimate its benefit and underestimate its side effects (Shin et al., 2019).

How it compares with dutasteride and topical finasteride

Dutasteride is in the same drug class. It is not FDA-approved for hair loss, and after the 2025–2026 reviews it carries a mood-change warning as a precaution (EMA, 2025; MHRA, 2026). Its US label says sexual side effects may persist after stopping, and that the drug's role in this is unknown (Avodart prescribing information).

In a 24-week trial of 458 men, a finasteride 0.25% skin spray gave peak blood levels more than 100 times lower than tablets and lowered blood DHT less (34.5% vs 55.6%). Treatment-related sexual side effects were reported in 2.8% of men on the spray, 3.3% on placebo and 4.8% on oral finasteride; the trial was not designed to show a difference between these groups (Piraccini et al., 2022). The trial was sponsored by the manufacturer and was too short to study persistence. Whether sexual side effects are rarer with the spray is not established. There is no FDA-approved topical finasteride, and the FDA has received reports of side effects that continued after stopping compounded topical products (FDA, 2025).

Other label warnings

• Finasteride lowers PSA, a blood test used in prostate cancer screening. The Proscar (5 mg) label says it lowers PSA by about 50%, and the Propecia label says any confirmed rise in PSA while taking it should be evaluated. Tell whoever orders a PSA test that you take finasteride.
• The label warns that 5-alpha reductase inhibitors may increase the risk of high-grade prostate cancer.
• Male breast cancer has been reported. The label states that the relationship between long-term use and male breast cancer is unknown. Breast tenderness and enlargement are also listed, and the label asks men to report any breast lumps, pain or nipple discharge.
• The label lists male infertility and poor semen quality among post-marketing reports, and states that semen quality has been reported to normalise or improve after stopping. Ejaculate volume fell by a median 0.3 mL (11%) over 48 weeks in one study, compared with 0.2 mL (8%) on placebo.
• Testicular pain, blood in semen, and hypersensitivity reactions (rash, itching, hives, and swelling of the lips, tongue, throat or face) are also listed (Propecia prescribing information).

Finasteride is not approved for hair loss in women; its use there is off-label. See the FAQ "What does finasteride do to the female body?" for more.

If you take it or are considering it

Finasteride is a prescription-only medicine, and whether to take it is a decision to make with a prescriber. The UK regulator (MHRA, May 2026) advises stopping finasteride 1 mg immediately and contacting a doctor if depression or suicidal thoughts develop. If you have thoughts of harming yourself, seek emergency help right away. Report any sexual, mood, cognitive, breast or other changes to your prescriber, whether they start during treatment or after stopping.

Finasteride is contraindicated in pregnancy: it can cause abnormal development of the external genitals in a male fetus. Women who are or may become pregnant must not take finasteride and must not handle crushed or broken tablets, because the active drug can be absorbed through the skin. Intact, coated tablets are not a handling risk.

References:

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