OnePin Peptide Library · Hormonal
Proviron (Mesterolone)
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.
How it works
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.
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.
What to expect
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.
Evidence
Interactions & stacking
What's safe to combine, and what belongs in a separate pin.
Keep separate
Side effects & safety
Commonly reported
- Accelerated hair loss in genetically predisposed users (strong DHT effect)
- Oily skin and acne
- Mild suppression of endogenous testosterone (dose-dependent)
- Possible libido surge - sometimes excessive
Less common & notes
- Prostate enlargement in susceptible users, mood changes, minimal lipid shift (milder than 17-aa orals), very rare hepatic stress markers.
- Women: contraindicated due to virilization risk at any meaningful dose.
- Rare: priapism (prolonged erection) at very high doses, exacerbation of prostatic disease.
Pharmacokinetics
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.
Regulatory status
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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The guide & community
The complete Proviron (Mesterolone) walkthrough, real protocol discussion and coaching live inside the BlessUp community on Skool.
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