Anabolic steroidEstrogenEstradiol esterGrowth promotantVeterinary implant

Estradiol Benzoate (Cattle Implant)

Also known as Synovex (component) · Revalor (component) · EB

Written by enwyReviewed 15 Jul 20261 sources0 comments

Estradiol benzoate is the estrogenic component of many combination cattle growth-promotant implants (e.g. Synovex, Revalor), usually paired with an androgen such as testosterone propionate or trenbolone acetate. It drives weight gain in cattle through the GH/IGF-1 axis and has no androgenic PED value in humans.

01 Overview

Estradiol benzoate is a short-ester estrogen used in subcutaneous ear-implant blends to promote growth in feedlot cattle. Its anabolic action in ruminants is largely indirect, working through increased growth hormone and IGF-1 rather than direct muscle androgen signalling.

In humans it is simply an estrogen; any exposure produces feminising, gonad-suppressing effects with no muscle benefit. It is included as a core veterinary growth-implant hormone and a significant residue/endocrine-disruptor and detection subject, and it is banned as a growth promotant in the EU.

02 Mechanism

Estrogen-receptor agonist; in cattle it raises pituitary growth-hormone output and hepatic IGF-1, increasing nitrogen retention and weight gain, typically synergising with a co-implanted androgen.

03 Dosing

Tier	Dose	Route	Notes
Cattle implant component	10–28 mg	SubQ	Per-animal implant estrogen content; not a human recommendation

Ester comparison

Ester	Half-life	Injection freq.	Testosterone by mass

04 Effects

Effect	Magnitude	Evidence
Increased weight gain (cattle)Improves average daily gain and feed efficiency, especially combined with an androgen.	+5-10% ADG	Clinical
GH/IGF-1 stimulationRaises growth hormone and IGF-1, the main anabolic pathway in ruminants.		Preclinical

05 Side effects

Effect	Severity	Frequency	Evidence	Countermeasures
Feminisation / estrogenic effectsGynecomastia, testosterone suppression and feminisation with no anabolic benefit in humans.	Moderate	Expected with human exposure	Clinical
Residue / endocrine-disruptor concernEstrogen residues in beef are the basis of the EU ban and ongoing endocrine-disruptor debate.	Moderate	Regulatory concern	Observational

06 Legal status

Banned hormonal growth promotant

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

United States

FDA-approved cattle implant component

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

07 References

Estradiol implants and growth promotion in cattleJournal of Animal Science

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.