No — DHT derivative; no C4-C5 double bond for aromatisation
Route
Oral — 17α-alkylated (hepatotoxic at high dose/long duration)
QSC format
Research tablet kits ≥99% HPLC — Janoshik COA
Mechanism of Action
Mesterolone is unique in the oral androgen class: it is pharmacologically more similar to an anti-oestrogenic agent than a classic anabolic steroid. The 1α-methyl group provides oral bioavailability without strong anabolic AR activation in muscle — because mesterolone is rapidly reduced by 3α-HSD in muscle tissue to a less active metabolite, unlike 17α-methylated steroids that resist this reduction. Primary mechanisms: (1) SHBG competitive binding — similar to stanozolol, mesterolone binds SHBG with high affinity, displacing testosterone and increasing free testosterone. (2) Anti-oestrogenic — mesterolone does not aromatise and may competitively inhibit aromatase at high concentrations. (3) Androgenic support — binds AR in androgenic tissues (prostate, seminal vesicles) with moderate affinity. Research utility: SHBG biology, studying the SHBG/free androgen relationship, anti-oestrogenic androgen research without anabolic confounds.
Key Research Studies
Study
Finding
Schürmeyer et al. 1983 (Clin Endo)
Mesterolone in hypogonadal men: testosterone and SHBG effects quantified — foundational clinical pharmacology
Nieschlag et al. 2009 (Eur J Endo)
Review of mesterolone for male hypogonadism — SHBG binding mechanism and role in increasing free testosterone fraction
3α-HSD inactivation (Liao 1977)
Mesterolone muscle metabolism: rapid 3α-reduction to 3α-hydroxy product in muscle but not androgenic tissues — explains low anabolic activity despite androgenic classification
Research Protocol Design
SHBG binding assay
Mesterolone vs stanozolol vs testosterone: competitive SHBG binding (purified SHBG + [3H]-DHT displacement). Ki determination. Compare SHBG binding affinity across androgens — mesterolone and stanozolol expected highest vs testosterone.
Tissue-specific 3α-HSD activity
Mesterolone metabolism in incubations of muscle homogenate vs prostate homogenate. HPLC quantification of 3α-hydroxy metabolite production. Establishes tissue-selectivity of mesterolone inactivation — explains the androgenic-without-anabolic profile.
Free testosterone modulation
In vitro: mesterolone 1-100nM + SHBG + testosterone. Measure free testosterone fraction by equilibrium dialysis. Establishes dose-response for SHBG displacement and free testosterone liberation.
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Frequently Asked Questions
Why is Proviron (mesterolone) considered non-anabolic?
Mesterolone is rapidly reduced by 3α-hydroxysteroid dehydrogenase (3α-HSD) in muscle tissue to a less active 3α-hydroxy metabolite — preventing significant AR activation in muscle. In androgenic tissues (prostate, seminal vesicles) where 3α-HSD activity is lower, mesterolone retains androgenic activity. This tissue-selective metabolism explains the androgenic-without-anabolic profile.
How does mesterolone increase free testosterone?
Mesterolone competitively binds SHBG (sex hormone-binding globulin) with high affinity, displacing bound testosterone. Since SHBG-bound testosterone is not bioavailable to AR, displacing it from SHBG increases the free testosterone fraction available for receptor activation. This is the primary mechanism for mesterolone’s testosterone-supporting effects in research models.
Is mesterolone anti-oestrogenic?
Mesterolone does not aromatise (DHT derivative). Some data suggests it may competitively inhibit aromatase at high concentrations — but this is not its primary mechanism. Its “anti-oestrogenic” research utility is more about increasing free testosterone (AR competition with ERα) and preventing aromatisation of displaced testosterone from SHBG.
