Mesterolone
Mesterolone, marketed as Proviron, is an orally active androgen derived from dihydrotestosterone (DHT). It is methylated at the 1-alpha position (NOT 17-alpha-alkylated like most oral AAS), which allows oral bioavailability without the classic 17-aa hepatotoxic profile. Developed by Schering in 1934 and introduced clinically in 1966, it remains medically approved in many countries (though not the US since 2006) for male hypogonadism, subfertility, and libido support.
Split daily dose into 2-3 evenly spaced doses given the ~12 hour half-life. Typically used throughout a testosterone-based cycle rather than as a standalone compound. Well-tolerated with minimal side-effect burden when used alone.
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
Mesterolone binds the androgen receptor (AR) with moderate affinity and produces direct androgenic effects similar to DHT. As a DHT derivative, it does not aromatize to estrogen and has no intrinsic estrogenic activity.
Its most useful pharmacologic feature is strong sex-hormone binding globulin (SHBG) affinity - it binds SHBG tightly, displacing testosterone and raising free (biologically active) testosterone from any co-administered testosterone base. This is why it is a common adjunct in cutting cycles rather than a standalone anabolic.
It also exhibits mild aromatase-competition activity, reducing estrogen conversion from aromatizable compounds (testosterone, methandrostenolone). This does not replace a dedicated aromatase inhibitor at higher testosterone doses but can reduce the required AI dose.
Unlike most oral AAS, mesterolone is 1-alpha-methylated rather than 17-alpha-alkylated. This unusual modification allows oral activity without significant hepatotoxicity - liver enzyme elevation is typically mild. HPT-axis suppression is dose-dependent but generally milder than other AAS.
First week: libido effect often noticeable within 3-5 days. Mood may lift slightly. No visible physique change yet.
Weeks 2-6: subtle muscle hardness improvement, sustained libido effect. Scale weight does not change significantly.
Weeks 7-12: stable effects throughout the cycle. Proviron is a 'background' compound - the benefit is cumulative but never dramatic.
Each reference below was re-fetched from its PubMed record, and the quoted sentence was confirmed to appear in that abstract and to support the claim it sits under. Follow any of them to read the source.
The response to Mesterolone, in doses of 25 mg/day, was examined in 42 pathospermic patients.
The response to Mesterolone, in doses of 25 mg/day, was examined in 42 pathospermic patients.
Mesterolone treatment of patients with pathospermia.
Evidence scope. Human pathospermia study; dose is stated, but the abstract does not state route or support 1-3 daily dosing.
Claims we could not support
No abstract we checked supports these for this molecule at this route. That is not the same as saying they are false — it marks where the evidence is missing.
Complete regimen: 25mg via Oral, 1-3x daily. The verified row supports only the narrower dose/route boundary stated above, not every element of the displayed regimen.
Mechanism: Mesterolone binds the androgen receptor (AR) with moderate affinity and produces direct androgenic effects similar to DHT. As a DHT derivative, it does not aromatize to estrogen and has no intrinsic estrogenic activity.. No checked live abstract supported this full mechanistic claim at the card's formulation/route without extrapolation.
Primary safety claim: Accelerated hair loss in genetically predisposed users (strong DHT effect). No checked live abstract directly established this as the primary concern for the card's exact formulation and regimen.
Oral
Per dose - supports 2-3x daily dosing
Hepatic metabolism. Renal excretion of metabolites.
Storage. Store at controlled room temperature (20-25°C / 68-77°F). Protect from moisture and light. Keep in original container. Keep out of reach of children and in a locked location - Schedule III controlled substance in the United States.
Schedule III controlled substance in the United States under the Anabolic Steroids Control Act of 1990. FDA approval was withdrawn in 2006 for commercial reasons; the compound was never banned for safety. Remains medically approved in most of Europe, Asia, and Latin America under the Proviron brand (Bayer / Schering) for hypogonadism and subfertility. Possession or distribution without a valid prescription is a federal offense in the United States.
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