Zeranol
Zeranol (Ralgro) is a non-steroidal resorcylic acid lactone growth promotant derived from the fungal mycotoxin zearalenone. It is a potent, orally and subcutaneously active estrogen agonist implanted in beef cattle and sheep to increase weight gain and feed efficiency. It has no legitimate human use and is banned as a growth promotant in the EU.
01 Overview
Zeranol is manufactured by reduction of zearalenone, a mycoestrogen produced by Fusarium moulds. Marketed as Ralgro subcutaneous ear implants, it binds estrogen receptors and drives anabolic weight gain in ruminants primarily through an estrogenic, not androgenic, mechanism, often by stimulating endogenous growth hormone and IGF-1 axis activity.
Because its action is estrogenic rather than androgenic, zeranol is not a muscle-building agent in the anabolic-androgenic sense and has essentially no rational bodybuilding application; diversion is rare and misguided. Regulatory interest centres on residues in meat and on endocrine-disruptor concerns, with several studies linking zeranol exposure to proliferation of estrogen-sensitive breast cell lines.
02 Mechanism
Binds and activates estrogen receptors alpha and beta as a potent xenoestrogen, increasing pituitary growth-hormone secretion and hepatic IGF-1, which raises nitrogen retention and weight gain in cattle.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Cattle implant (veterinary) | 36–72 mg | SubQ | Ear implant per animal; not a human dosing recommendation |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Increased weight gain (cattle)Raises average daily gain and feed conversion efficiency in implanted ruminants. | +5-15% ADG | Clinical | |
| GH/IGF-1 axis stimulationIncreases circulating growth hormone and IGF-1 in treated animals, the presumed anabolic driver. | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Estrogenic endocrine disruptionActs as a potent xenoestrogen; in humans could cause gynecomastia, HPTA disruption and feminisation with no anabolic benefit. | Moderate | Expected with exposure | Preclinical | |
| Proliferative effect on estrogen-sensitive tissueIn vitro studies show zeranol stimulates proliferation of estrogen-receptor-positive human breast epithelial and cancer cell lines. | Severe | Uncertain in humans | Preclinical |