Medication questions Finasteride
Does finasteride lower testosterone?
Short answer
No. Finasteride lowers DHT, not testosterone. It blocks the enzyme that turns testosterone into DHT, so less testosterone is converted, and studies of this class of medicine have found testosterone tends to rise modestly rather than fall. Sexual side effects can still happen, and the MHRA warns that some may persist after stopping.
Key facts
- Finasteride blocks type II 5-alpha-reductase, lowering DHT rather than testosterone.
- Finasteride 1 mg lowered blood DHT by about 71% in a 42-day study (Drake 1999).
- In a 4-year trial of the 5 mg prostate dose, testosterone rose modestly compared with placebo.
- MHRA warnings on mood and sexual side effects apply whatever your testosterone level.
How finasteride works
Testosterone is converted into a more potent hormone, DHT (dihydrotestosterone), by an enzyme called 5-alpha-reductase. In men with a genetic tendency to male pattern hair loss, DHT gradually shrinks scalp hair follicles.
The UK summary of product characteristics (SmPC) describes finasteride as "a competitive and specific inhibitor of type II 5α-reductase". Blocking it "blocks the peripheral conversion of testosterone to the androgen DHT", lowering DHT in the blood and in tissues such as the scalp.
In a 1999 study of 249 men with hair loss, 42 days of finasteride 1 mg lowered blood DHT by 71.4% and scalp DHT by 64.1%. Finasteride does not stop your body making testosterone.
What happens to testosterone
Because less testosterone is being converted to DHT, testosterone levels tend to go up slightly rather than down.
The UK Propecia SmPC does not give a figure for testosterone at the 1 mg dose. The clearest long-term data come from the higher prostate dose: in a 4-year placebo-controlled trial of finasteride 5 mg in men with an enlarged prostate, finasteride produced "a modest but significant increase" in blood testosterone compared with placebo, most noticeably in men who started with lower levels. For dutasteride, which blocks both types of the enzyme, the UK Avodart SmPC reports a median testosterone rise of 19% at 1 and 2 years.
So the reassuring answer to the search question is that finasteride is not known to cause low testosterone.
Why sexual side effects can still happen
A normal testosterone level does not rule out side effects. The MHRA's Drug Safety Updates of 29 April 2024 and 11 May 2026 say finasteride is associated with "low mood, depression, suicidal thoughts and sexual dysfunction (decreased sex drive, erectile dysfunction and ejaculation disorders)", and that sexual dysfunction may persist after treatment is stopped. Why this happens in some men is not fully understood.
The MHRA advises stopping finasteride 1 mg immediately and contacting your doctor if you develop depression or suicidal thoughts, and contacting your doctor about any sexual side effects. Our pages on persistent sexual side effects and finasteride and depression explain more.
Blood tests while you take finasteride
If you are having hormone tests, tell whoever orders them that you take finasteride. Your DHT will be lower than usual because that is how the medicine works, and a slightly higher testosterone is not unusual. WMG Healthcare explains what a DHT test measures and offers a testosterone blood test if you want to check your levels.
Finasteride also lowers PSA, a prostate blood test, so it needs adjusting when read. See finasteride and the PSA test. If you are on, or considering, testosterone treatment, read finasteride and testosterone replacement therapy and raise it at your free assessment.
Want an answer for your own situation?
A GMC-registered doctor can review your history and medicines and tell you what would suit you, including whether treatment is right for you at all. The assessment and review are free.
Start your free assessment →Related questions
Does finasteride raise testosterone?
Slightly, in most studies of this class of medicine. Because less testosterone is converted to DHT, blood testosterone tends to rise modestly. The UK product information for the 1 mg dose does not give a figure, so treat it as a small effect rather than a predictable number.
Is low libido on finasteride a sign of low testosterone?
Not necessarily. Low sex drive is a recognised side effect of finasteride itself, and it can also come from stress, low mood, alcohol or other health problems. Tell your prescriber. A testosterone blood test can help rule out low testosterone as a separate cause.
Can I check my testosterone while taking finasteride?
Yes. Tell the person ordering the test that you take finasteride, because it lowers DHT and can nudge testosterone up. A morning blood test is usually used for testosterone.
Does dutasteride lower testosterone?
No. The UK Avodart product information reports a median 19% rise in testosterone at 1 and 2 years. Like finasteride, dutasteride lowers DHT, and it carries its own warnings about sexual side effects that may persist after stopping.
Can finasteride cause breast changes?
Breast tenderness or enlargement can happen, and male breast cancer has been reported in men taking finasteride 1 mg. The product information asks you to report any lumps, pain, enlargement or nipple discharge promptly. See finasteride and breast changes.
Sources
- Propecia 1 mg: summary of product characteristics, section 5.1 (eMC, revised 29 June 2026)
- Drake L et al. The effects of finasteride on scalp skin and serum androgen levels in men with androgenetic alopecia. J Am Acad Dermatol 1999
- Roehrborn CG et al. Effects of finasteride on serum testosterone and body mass index in men with benign prostatic hyperplasia. Urology 2003
- Avodart 0.5 mg soft capsules: summary of product characteristics, section 5.1 (eMC, revised 11 August 2026)
- MHRA Drug Safety Update, 11 May 2026: Finasteride and dutasteride, updated safety warnings
Facts checked against these sources on 4 October 2026. This page is general information, not personal medical advice. Read our editorial policy.