Mesterolone (Proviron)

What this is

Schering (now Bayer) Proviron — developed 1960s; introduced for medical use 1967. The distinguishing pharmacology is the 1α-methyl substitution that confers oral bioavailability WITHOUT the C17α-alkylation that gives most oral AAS their characteristic hepatotoxicity — making mesterolone the mildest oral DHT-derivative on hepatic stress (compare with Winstrol/Anadrol/Dianabol). Already 5α-reduced so not a 5α-reductase substrate; NOT aromatizable. **Primary biohacker use case** is as a TRT adjunct: SHBG-binding displaces testosterone from SHBG, raising the free-T fraction; the libido/erectile-quality signal in clinic practice is real but only loosely supported by RCTs. **Monotherapy efficacy is weak**: Nieschlag 1989 (Hum Reprod) — the largest infertility RCT (n=248 couples; 6 months) showed sperm parameter improvement but NO pregnancy benefit. Comhaire 1991 (Fertil Steril) high-dose mesterolone confirmed limited efficacy. **Safety profile vs other orals**: lower hepatotoxicity than C17α-alkylated orals; comparable or worse HDL suppression to other DHT derivatives; strong androgenic effects accelerate androgenetic alopecia and worsen BPH in predisposed men. **Modern trend**: increasingly displaced by aromatase inhibitors (anastrozole) for estrogen control on TRT — Proviron's SHBG-lowering use case remains niche. **NOT FDA-approved in US** — only available via international sources or research-chemical channels; legal risk applies. Distinct from Masteron (drostanolone) — Masteron is injectable, used pre-contest; Mesterolone is oral, used as a TRT adjunct.

Mechanism

1α-methyl-DHT derivative; orally bioavailable via 1α-methyl substitution rather than the more hepatotoxic 17α-alkylation typical of oral AAS; androgen receptor agonist with strong androgenic and weak anabolic profile (inactivated by 3α-HSD in skeletal muscle limits muscle-building effect); NOT a 5α-reductase substrate (already 5α-reduced); NOT aromatizable to estrogen; high SHBG-binding affinity displaces testosterone → increases free testosterone fraction; mild anti-estrogenic activity via 3β-HSD interference

Dose & route

Therapeutic 25-75 mg/day PO divided; TRT-adjunct biohacker use typically 25-50 mg/day; historical infertility protocols 100 mg/day; take with food

Citations

• https://pubmed.ncbi.nlm.nih.gov/2680994/
• https://pubmed.ncbi.nlm.nih.gov/1900485/
• https://go.drugbank.com/drugs/DB13587
• https://www.wada-ama.org/en/prohibited-list
• https://pubmed.ncbi.nlm.nih.gov/15705014/

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