Mesterolone
DHT-derived oral androgen with uniquely low anabolic muscle tissue activity due to extensive inactivation by 3α-HSD in muscle. Used clinically for male hypogonadism and infertility. Valued as a cycle ancillary: lowers SHBG (freeing more testosterone), mildly inhibits aromatase, and improves mood/libido.
Mechanism of Action
Binds androgen receptor but is rapidly inactivated by 3α-hydroxysteroid dehydrogenase in skeletal muscle — explaining weak direct anabolic effect. Strong SHBG displacement frees circulating testosterone. Mild competitive aromatase inhibition. Does NOT significantly suppress HPTA at typical doses. DHT derivative means no conversion to estrogen.
Typical Dosing
⚠ Warning Flags
- •Accelerates androgenic alopecia (DHT-derived)
- •Weak liver stress but still 17α-methylated
Effect Profile
Side Effect Profile
Research Studies
Mesterolone therapy in oligospermic patients: hormonal and seminal parameters
Foresta C, et al. · 1983
Mesterolone improved sperm motility and seminal parameters in oligospermic men without significantly suppressing LH/FSH, documenting its unique 'fertility-friendly' hormonal profile compared to other androgens.
Pharmacokinetics of mesterolone — oral bioavailability and inactivation in muscle
Rolf C, et al. · 1996
Demonstrated mesterolone's rapid inactivation by 3α-HSD in skeletal muscle, explaining its lack of direct myotrophic effect despite androgenic receptor binding — unique among AAS.