Compounds / TRT and hormones

Proviron

Mesterolone (1α-methyl-DHT)

Oral DHT-derived anabolic-androgenic steroid (1α-methyl-dihydrotestosterone) developed by Schering in 1934 and marketed as Proviron 25mg tablets since 1967. Never marketed in the United States; classified as a Schedule III anabolic steroid under the 1990 Anabolic Steroid Control Act. Widely available in EU, UK, Australia, South Africa, Russia, and most LATAM/SEA markets as a prescription drug for male hypogonadism and infertility. In TRT and bodybuilding context, valued NOT for direct anabolic effect (mediocre) but for SHBG displacement: increases free testosterone by binding SHBG with high affinity and freeing bound T.

At a glance

Half-life

~12.5 h Terminal serum t½ 12-13h (Bayer Proviron SmPC); supports BID dosing for sustained SHBG occupancy. Tmax ~1.6h. Resistant to hepatic 17α-oxidation due to 1α-methyl group: not 17α-alkylated, so hepatotoxicity risk is LOWER than typical oral AAS. Oral bioavailability ~3% per Bayer SmPC; compensated by hepatic resistance.

Routes

Oral

Evidence base

2 studies 2 review

Mechanism

Three pharmacologically meaningful actions: (1) High-affinity SHBG binding (58% of bound drug is SHBG-bound): displaces testosterone from SHBG → ↑ free T (the primary clinical utility on TRT). (2) Weak androgen receptor agonist: modest direct anabolic / androgenic effect; cannot aromatize (DHT-derived). (3) Mild aromatase inhibition: competitive substrate at aromatase, reduces conversion of co-administered androgens to estradiol. PK, approved indications, and hepatotoxicity profile documented in SMPC. Net effect: increases bioavailable T, decreases E2, modest improvement in libido and well-being.

Dosing

Where a study reports an amount, it appears in that study's entry below, attributed to the source.

Published evidence

1. Review 2024

   Mesterolone (DB13587): mechanism, binding profile, interactions

   DrugBank DrugBank

   58% SHBG-bound (highest SHBG affinity of any oral AAS); weak AR agonist; no aromatization; mild aromatase substrate competition.

2. Review 2023

   Proviron 25mg Tablets: Summary of Product Characteristics

   Bayer Bayer SmPC

   PK (Tmax ~1.6h, t½ 12-13h, oral BA ~3%), SHBG-binding pharmacology, indications (male hypogonadism, infertility), dosing 25-75mg/day. Primary regulatory source.

Reported side effects

Androgenic effects (oily skin, acne, hair loss)

Common Moderate · DHT-derivative: direct AR activation in skin, sebaceous, and scalp tissue. Worse in genetically predisposed users (AGA). NOT mitigated by finasteride (already DHT-derived; no 5-AR substrate).

Prostate enlargement / elevated PSA

Occasional Moderate · DHT-class effect: monitor PSA in men >40 on chronic use.

HPTA suppression at higher doses (50-100mg/day)

Common Moderate · Mild AR-mediated negative feedback at >50mg/day. Less suppressive than testosterone or nandrolone but not zero.

Reduced HDL cholesterol

Common Moderate · Oral AAS lipid pattern: HDL drops, LDL may rise. Monitor lipids on chronic use.

Virilization in women

Very common Serious · Contraindicated in women: voice deepening, clitoromegaly, and hirsutism are likely permanent at any meaningful dose.

Priapism

Rare Serious · Reported in Bayer SmPC adverse events: sustained painful erection requires emergency intervention.

Mood changes / aggression

Occasional Moderate · Anecdotal: DHT-derivative androgens commonly reported as mood-elevating or 'edgy' at higher doses.

Interactions

• Test Cypionate Synergy

  Mesterolone displaces TRT-administered T from SHBG → free T elevation without raising total T. The standard 'feels better on TRT' add-on.

• Anastrozole Caution

  Both reduce E2: mesterolone via mild aromatase competition + SHBG displacement (raises free T but reduces aromatase substrate ratio). Risk of E2 over-suppression.

• Finasteride Caution

  Finasteride blocks 5α-reductase but mesterolone is ALREADY a DHT derivative: finasteride does NOT mitigate mesterolone's androgenic side effects.

• Warfarin Caution

  Anabolic steroids potentiate warfarin anticoagulation: INR can rise unpredictably.

• Drostanolone Redundant

  Both are DHT derivatives with overlapping AR-binding and side effect profile. Stacking amplifies androgenic SE without proportionate benefit.

Storage

Room temperature, dry, original blister.