Mesterolone, sold as Proviron, is an oddity among anabolic steroids. It is taken by mouth yet barely troubles the liver, it is androgenic but builds little muscle, and its best-known trait in gym culture is something it does to a carrier protein in the blood. Understanding it means understanding what it does not do as much as what it does.
- Mesterolone is a DHT derivative with a methyl group at the 1-position, which lets it work orally without the 17-alpha-alkyl group that stresses the liver.
- It was prescribed in some countries for low testosterone and certain forms of male infertility, as 25 mg tablets.
- It binds sex hormone-binding globulin (SHBG) strongly, which can raise free levels of other hormones.
- It is a weak muscle builder; its main risks are androgenic: hair, skin, prostate and cholesterol.
A medicine with a narrow purpose
Mesterolone was introduced in the 1930s and later marketed by Schering as Proviron. Doctors in Europe and elsewhere used it for men with low androgen levels and for some men with poor sperm quality, on the theory that a mild androgen could help without shutting down the testes as strongly as testosterone. The evidence for the fertility use was mixed, and it was never a mainstream North American medicine.
Why the liver tolerates it better
Most oral anabolic steroids survive the first pass through the liver because of a 17-alpha-alkyl group, and that same group is what makes them hard on liver cells. Mesterolone uses a different modification, a methyl group at the first carbon, which slows its breakdown without the same toxicity. Liver enzymes are therefore less likely to rise than with Dianabol, Anadrol or Winstrol, though not impossible, especially alongside other orals or alcohol.
The SHBG effect
Sex hormone-binding globulin is a protein that carries testosterone and estradiol in the blood and keeps most of them inactive. Mesterolone binds SHBG very strongly, which displaces other hormones and raises the free, active fraction. This is why it is described as making other compounds “work better”. It is also why total testosterone tests can be misleading while using it; free testosterone and SHBG should be measured too.
Does it lower estrogen?
Mesterolone cannot be converted to estrogen, and some users believe it acts as an anti-estrogen. The evidence for a meaningful anti-estrogen effect in people is weak. It should not be relied on to manage high estradiol; if estrogen-related symptoms appear, a sensitive estradiol test and a doctor’s opinion are the right steps.
Side effects
Hair and skin
As a DHT derivative, mesterolone can accelerate male-pattern hair loss and increase oil production and acne. Finasteride will not block it, because it is already DHT-like. Our article on hair loss explains the mechanism.
Prostate
DHT-type androgens stimulate prostate tissue. Men over 40, or with urinary symptoms, should have a PSA test and a conversation with a doctor before using any androgen.
Cholesterol and blood pressure
HDL can fall and blood pressure can rise, as with most androgens, though often less dramatically than with 17-alpha-alkylated orals.
Suppression
Mesterolone suppresses the body’s own testosterone less than many compounds at medical amounts, but suppression is not zero, and higher amounts suppress more.
Strongly androgenic compounds carry a high risk of virilisation in women. Voice changes and clitoral enlargement can be permanent.
What it does not do
Mesterolone does not build significant muscle. In the body, it is largely broken down in muscle tissue before it can act strongly there. People expecting size from it are usually disappointed. Its effects, where noticed, are on libido, mood and how other hormones behave.
Bloodwork to discuss with a doctor
| Marker | Why it matters with mesterolone |
|---|---|
| Total testosterone, free testosterone, SHBG | SHBG drops can make total levels misleading |
| Estradiol | To check symptoms rather than guess |
| Lipid panel | HDL changes |
| PSA (men over 40) | Prostate stimulation |
| Liver enzymes | Baseline, especially alongside other orals |
Zionova, 20 mg x 50Proviron (Mesterolone)View product
Legal status in Canada
Mesterolone is a Schedule IV anabolic steroid under the Controlled Drugs and Substances Act. Importing, exporting and trafficking are offences; simple possession of Schedule IV substances is not. This is general information, not legal advice.
Frequently asked questions
Is Proviron hard on the liver?
Less than most oral steroids, because it is not 17-alpha-alkylated. Liver enzymes should still be checked, particularly if other orals or alcohol are involved.
Does Proviron increase libido?
Some users report it. Effects on libido vary, and low libido can have many causes worth investigating with bloodwork.
Will Proviron stop gynecomastia?
It is not a reliable estrogen blocker. Gynecomastia symptoms need proper evaluation.
Educational information only. Nothing here is medical advice or a recommendation to use any product. Anabolic steroids are Schedule IV under the Controlled Drugs and Substances Act. Talk to a doctor and get bloodwork before and after using any compound.
