Long-term finasteride and dutasteride side effects

Taken finasteride or dutasteride for years? The risk the UK finasteride leaflets spell out is sexual, and it can last: erection, sex drive and ejaculation problems may continue after stopping. This is part of post-finasteride syndrome (PFS).

A 2020 review went further. It linked these medicines to the liver, blood sugar, eyes and kidneys. We read the studies behind it: in people, the evidence is for blood sugar and liver fat, and much of the rest comes from animal studies.

Which of these risks have actually been seen in people?

What did the 2020 review claim?

It argued that long-term use “may be associated with” fatty liver, insulin resistance, type 2 diabetes, dry eye disease and possibly kidney disease. The review, by Abdulmaged Traish of Boston University, appeared in the World Journal of Men’s Health.

His idea is simple. Both medicines block the enzyme that turns testosterone into DHT, a stronger hormone. Traish suggests that tissues such as the liver and eyes then run short of DHT, even when testosterone in the blood looks normal.

It’s one author’s review and hypothesis, not a new study. For the kidneys and eyes, it leans mainly on preclinical work: animal studies that haven’t been repeated in people. Some of its human evidence comes from men with low testosterone or on hormone treatment for prostate cancer, not from finasteride or dutasteride users.

The kidney claim rests on one animal study. In rats, finasteride was linked to scarring and inflammation in the kidneys. We found no study of kidney disease in people taking these medicines.

Do finasteride and dutasteride raise the risk of diabetes?

One large study suggests a modest rise. Researchers used UK GP records of men treated for an enlarged prostate and followed them for several years.

New type 2 diabetes appeared in about 8 in 1,000 men a year on finasteride or dutasteride, against about 6 in 1,000 on tamsulosin, a prostate medicine that works differently. Taiwanese records pointed the same way.

The study, published in the BMJ in 2019, can’t prove the medicines caused it. The authors wrote that extra monitoring “might be required” for men starting them, especially men with other diabetes risk factors.

An earlier Taiwanese study found the opposite: fewer new cases in users under 65. So the picture isn’t settled. Both studies looked at older men on prostate doses. For younger men taking 1 mg for hair loss, there’s less evidence either way.

Can they affect the liver?

The UK leaflets already say so in general terms. Both the Propecia (1 mg) and Proscar (5 mg) leaflets list “changes in the way your liver is working, which can be shown by a blood test”. They don’t say how often.

The fatty liver claim comes from a small trial. Healthy men took finasteride or dutasteride for three weeks, with liver scans before and after. On dutasteride, fat built up in the liver and the liver responded less well to insulin. Finasteride didn’t have that effect.

A three-month trial in Edinburgh found a related effect outside the liver. On dutasteride, the body’s tissues responded less to insulin and body fat rose a little. Finasteride didn’t do this. The researchers think this is because dutasteride blocks both forms of the enzyme, and finasteride only one.

We found no long-term study of liver disease in users.

What can I do?

These medicines help many people. If you’re worried about side effects, that’s a decision for you and your prescriber.

If your mood drops or you have suicidal thoughts, the Propecia leaflet says to stop taking it and contact your doctor as soon as possible. The Samaritans are on 116 123, free, at any hour.

If you’ve taken either medicine for years, especially with other diabetes risk factors, you can raise it at your next GP visit.

Report it: it helps everyone

A doctor’s note helps you. A report to the medicines regulator helps everyone else: it is how patterns get noticed.

• No proof needed. A suspicion is enough, even years after stopping.
• Where: the Yellow Card scheme in the UK, MedWatch in the US.
• Use the right words. If symptoms continued after stopping, write Post 5-alpha-reductase inhibitor syndrome (MedDRA 10082430).

Our reporting guide walks you through it

What else do people ask?

Can finasteride cause dry eyes? A 2025 records study of people with hair loss found dry eye in about 30 in 1,000 users, against about 26 in 1,000 non-users. It’s a signal, not proof. Our article on finasteride and the eyes covers more.

Is this the same as post-finasteride syndrome? No. PFS means symptoms that continue after stopping. It’s more than sexual problems: 2022 criteria also list problems with cognition, depression and suicidality, which can occur without sexual problems.

Do these effects go away after stopping? Nobody knows. The trials above measured men while they took the medicine, and none followed them after the last tablet. For the sexual side effects, the UK finasteride leaflets do say they may continue after stopping.

If you’ve been on finasteride or dutasteride for years and something has changed, report it. A report counts even years later.

Sources

1. Traish AM. Health risks associated with long-term finasteride and dutasteride use: it’s time to sound the alarm. World J Mens Health 2020;38(3):323-37. Single-author narrative review. Conclusion: long-term use “may be associated with health risks including NAFLD, IR, T2DM, dry eye disease and potential kidney disease”. Kidney and most eye and liver mechanism evidence is from rodents; some human evidence is from androgen deprivation therapy or low testosterone.
2. Wei L, Lai EC, Kao-Yang YH and colleagues. Incidence of type 2 diabetes mellitus in men receiving steroid 5α-reductase inhibitors: population based cohort study. BMJ 2019;365:l1204. UK CPRD 2003-14, mean follow-up 5.2 years: 76.2 (dutasteride) and 76.6 (finasteride) against 60.3 (tamsulosin) new cases per 10,000 person-years; adjusted hazard ratios 1.32 and 1.26. Taiwan NHIRD: 1.34 and 1.49.
3. Lee SS, Yang YW, Tsai TH and colleagues. 5-alpha-reductase inhibitors and the risk of diabetes mellitus: a nationwide population-based study. Prostate 2016;76(1):41-7. Under 65: hazard ratio 0.47 for type 2 diabetes in users against non-users over five years.
4. Hazlehurst JM, Oprescu AI, Nikolaou N and colleagues. Dual-5α-reductase inhibition promotes hepatic lipid accumulation in man. J Clin Endocrinol Metab 2016;101(1):103-13. 12 healthy men, finasteride 5 mg or dutasteride 0.5 mg for three weeks.
5. Upreti R, Hughes KA, Livingstone DE and colleagues. 5α-reductase type 1 modulates insulin sensitivity in men. J Clin Endocrinol Metab 2014;99(8):E1397-406. 46 men, dutasteride, finasteride 5 mg or tamsulosin for three months; body fat up 1.6% on dutasteride.
6. Lee CY, Yang SF, Chang YL and colleagues. The association between 5α-reductase inhibitors and the presence of subsequent dry eye disease in androgenetic alopecia: a TriNetX database study. Cureus 2025;17(12):e99288. 77,982 people in each group; dry eye in 2.97% against 2.60%; adjusted hazard ratio 1.08.
7. Baig MS, Kolasa-Wołosiuk A, Pilutin A and colleagues. Finasteride-induced inhibition of 5α-reductase type 2 could lead to kidney damage: animal, experimental study. Int J Environ Res Public Health 2019;16(10):1726. Male Wistar rats.
8. Propecia 1 mg, patient information leaflet, emc, last revised May 2026. Section 4, frequency unknown: “changes in the way your liver is working, which can be shown by a blood test”, and erection, sex drive and ejaculation problems that persist “after discontinuation of treatment”. Section 2: for mood changes, stop and contact your doctor.
9. Proscar 5 mg, patient information leaflet, emc. Section 4: the same liver line; erection, sex drive and ejaculation problems “may continue after stopping the medication”.
10. Healy D, Bahrick A, Bak M and colleagues. Diagnostic criteria for enduring sexual dysfunction after treatment with antidepressants, finasteride and isotretinoin. Int J Risk Saf Med 2022;33(1):65-76. Section 5: for finasteride, cognitive impairment, depression and suicidality can occur with or without sexual difficulties.