Finasteride

Is finasteride safe?

For most men, yes, but the risks are of a kind that matters to the people who take it. Finasteride blocks the enzyme that turns testosterone into DHT. At 1 mg a day (Propecia) it slows male pattern hair loss; at 5 mg (Proscar) it shrinks an enlarged prostate. Physically it is very forgiving: single doses up to 400 mg caused no harm in studies, and it barely interacts with other drugs.

The catches are sexual and psychiatric. A few percent of men get sexual side effects, some report they persist after stopping, and regulators in Europe and the UK now confirm a link to depression and suicidal thoughts. We score it 81, just above montelukast at 78, which has a similar profile of physical safety and mental health warnings.

What are the sexual side effects of finasteride?

The Propecia trials give the cleanest numbers. In the first year, among 945 men on 1 mg and 934 on placebo:

Side effect	Finasteride 1 mg	Placebo
Lower sex drive	1.8%	1.3%
Erectile dysfunction	1.3%	0.7%
Less ejaculate	1.2%	0.7%
Any of these	3.8%	2.1%

In those trials the effects went away in men who stopped and in most who carried on, and by the fifth year each had fallen to 0.3% or less. Since then, the US label has added reports of sexual dysfunction that continued after stopping, male infertility or poor semen quality, and testicular pain. By April 2024 the MHRA had 426 UK reports of sexual dysfunction with finasteride, and in almost half the man had not recovered when the report was made. Reports cannot show how often this happens, and patient groups use the term "post-finasteride syndrome" for persistent symptoms that medicine does not yet explain.

Depression and suicidal thoughts

The US label lists depression and suicidal ideation and behaviour among post-marketing reports. European regulators went further. In May 2025, after an EU-wide review that found 313 reports of suicidal thoughts with finasteride, the EMA's safety committee confirmed suicidal ideation as a side effect of the 1 mg and 5 mg tablets. The frequency is unknown, and the committee judged that benefits still outweigh risks for all approved uses. It found no link for the approved skin spray.

Packs of 1 mg tablets in the EU now carry a patient card. The UK introduced cards for both strengths in 2024 and in May 2026 added a warning that sexual side effects may contribute to low mood. The advice is clear: before starting, tell the prescriber about any history of depression; stop the 1 mg hair-loss tablet at once and contact a doctor if depression or suicidal thoughts appear; men on 5 mg should contact their doctor promptly. Tell people close to you that you take it, because others may notice mood changes first.

Prostate cancer and PSA tests

Finasteride roughly halves PSA results at the 5 mg dose, which can hide a rising PSA. The label says any confirmed increase from your lowest level should be checked, even if it is still "normal".

In the Prostate Cancer Prevention Trial of 18,880 men, finasteride 5 mg cut prostate cancer diagnoses by about a third (10.5% vs 14.9%) but high-grade cancers were slightly more common (3.5% vs 3.0%). After up to 18 years, survival was the same in both groups (15-year survival 78.0% vs 78.2%). The label carries a warning about high-grade cancer; the long-term data are reassuring on deaths.

Pregnancy and handling tablets

Finasteride can cause abnormal genitals in a male fetus. It is contraindicatedContraindicationA situation in which a medicine should not be used, because the risk clearly outweighs any benefit, such as a known allergy to it.More in the glossary in women who are or may become pregnant, and they should not handle broken or crushed tablets. Intact tablets are coated and safe to touch. It is not approved for women or children.

Topical finasteride and online prescribing

Hair-loss finasteride is now widely sold through telehealth services, often as compounded sprays or minoxidil mixes. On 22 April 2025 the FDA warned that no topical finasteride is approved in the US. It had received 32 reports to its adverse event database from 2019 to 2024 with compounded sprays and solutions, describing erectile dysfunction, low libido, anxiety, depression, suicidal thoughts, brain fog and testicular pain, and in most of them the problems continued after stopping. Finasteride is absorbed through the skin, and a spray or solution also carries a greater risk of transfer to a partner than coated tablets. A topical form is not automatically safer. For hair loss, some people also look at supplements such as biotin, which does not act on DHT and has little evidence outside deficiency.

Who should be careful

Talk to your doctor or pharmacist before starting finasteride if you have had depression, anxiety or suicidal thoughts, have sexual problems already, are trying for a baby, or have regular PSA tests. If you are already taking it and notice mood or sexual changes, contact your prescriber; for the 1 mg dose, UK and EU advice is to stop at once if depression or suicidal thoughts start. A lower score does not mean the drug is wrong for you, especially for prostate symptoms.

How we scored it

Overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (97), interactions (95) and dependence (95) are excellent. Regulatory warnings (50) reflect the 2025 EU referral, UK alerts and the FDA's warning on compounded products, though there is no US boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary. Serious side effects (62) weigh uncommon sexual effects, which can persist, and rare psychiatric harms against a large majority of men who have none.