Anabolic steroidOralProgestinFeed additiveGrowth promotant

Melengestrol Acetate

Also known as MGA · Melengestrol

Written by enwyReviewed 15 Jul 20261 sources0 comments

Melengestrol acetate (MGA) is a highly potent orally active progestin fed to feedlot heifers to suppress estrus and improve weight gain and feed efficiency. It is a growth-promoting progestational agent with no human therapeutic use; its relevance here is as a feed-additive growth promotant and a residue/detection concern.

01 Overview

MGA is a 17-alpha-acetoxy progesterone derivative many times more potent than natural progesterone. Administered as a low-dose feed additive, it inhibits ovulation and estrus in heifers while promoting anabolic weight gain and better feed conversion.

It is not an androgen and has no muscle-building value in humans; any human exposure would be progestogenic. It is closely monitored for tissue residues in beef and is banned as a feed additive in the EU. Its inclusion here reflects its status as a genuine veterinary growth agent rather than any PED utility.

02 Mechanism

Potent progesterone-receptor agonist that suppresses the hypothalamic-pituitary-gonadal axis to block estrus, indirectly improving anabolic efficiency in feedlot cattle.

03 Dosing

Tier	Dose	Route	Notes
Feedlot heifer feed additive	0.25–0.5 mg/day	Oral	Per-animal feed dose; not a human recommendation

Ester comparison

Ester	Half-life	Injection freq.	Testosterone by mass

04 Effects

Effect	Magnitude	Evidence
Improved weight gain (heifers)Increases average daily gain and feed conversion in feedlot heifers.	+6-10% feed efficiency	Clinical
Estrus suppressionBlocks estrus, reducing riding behaviour and improving pen performance.		Clinical

05 Side effects

Effect	Severity	Frequency	Evidence	Countermeasures
Tissue residue riskConcern over MGA residues in edible tissue underlies EU prohibition.	Mild	Regulatory concern	Observational
Progestogenic endocrine effectsIn humans this potent progestin would suppress gonadal function and libido with no anabolic gain.	Moderate	Uncertain in humans	Preclinical

06 Legal status

Banned hormonal growth promotant

Prohibited in food animals under Directive 96/22/EC · as of Jan 2026

United States

FDA-approved feed additive

Legal in feedlot cattle; no human approval · as of Jan 2026

07 References

Melengestrol acetate residues and safety evaluationJECFA / FAO monographs

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.