Penmesterol
Penmesterol (methyltestosterone 3-cyclopentyl enol ether) is an orally/parenterally used androgen ester-ether prodrug of methyltestosterone, marketed historically in some European markets. As a methyltestosterone derivative it is aromatisable, moderately androgenic, and shares the hepatotoxicity of 17-alpha-methylated orals; documented human medical use is limited and dated.
01 Overview
Penmesterol is the 3-cyclopentyl enol ether of methyltestosterone, designed to modify absorption and duration. On hydrolysis it delivers methyltestosterone, so its pharmacology is that of a classic aromatisable oral androgen used historically for androgen deficiency and related indications.
Because the active moiety is methyltestosterone, expect estrogenic conversion, moderate androgenic effect, and hepatotoxicity from the 17-alpha methyl group. It is essentially obsolete and appears only in older pharmacological literature.
02 Mechanism
Enol-ether prodrug hydrolysing to methyltestosterone, an aromatisable androgen-receptor agonist; 17-alpha-methyl group gives oral activity.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Historical | 10–30 mg/day | Oral | Old androgen-replacement dosing. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Androgen replacement effectsRestores androgenic effects via methyltestosterone. | moderate | Observational | |
| Lean mass/strengthAnabolic effect typical of methyltestosterone. | modest | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Estrogenic effectsWater retention and gynecomastia risk from aromatisation of methyltestosterone. | Moderate | Common | Observational | |
| HepatotoxicityRaised liver enzymes from the methylated active metabolite. | Moderate | Common | Observational | |
| HPTA suppressionSuppresses endogenous testosterone. | Severe | Universal | Observational |