Estradiol Cypionate
Estradiol cyclopentanepropionate
Also known as: Delestrogen · DepoEstradiol · Depogen · Dura-Estrin · ECP · E-Cypionate · Estra-D · Estrace · Estro-Cyp · Estroject · depGynogen · Femtrace · Gynodiol · beta-oestradiol · dihydrofolliculin · dihydrotheelin · dihydroxyoestrin · estradiolum · NSC-9895 · NSC-20293 · oestradiol cyclopentylpropionate · oestradiol cypionate
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pregnancy avoidance after mismating | 44 micrograms/kg (0.044 mg/kg) IM once; during day 4 estrus to day 2 of diestrus | IM | once | — | 🌎 NA |
- Pregnancy avoidance after mismating: Rarely used for this indication today as there are safer, more effective treatments. Toxic at >=100 micrograms/kg.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pregnancy avoidance after mismating | 250 micrograms/kg (0.25 mg/kg) IM once 6 days after coitus; or 0.25 mg/cat IM at 40 hours after coitus | IM | once | — | 🌎 NA |
- Pregnancy avoidance after mismating: Rarely used for this indication today as there are safer, more effective treatments.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| To enhance estrus behavior and receptivity in ovariectomized mares | 5-10 mg (total dose) IM once | IM | once | — | 🌎 NA |
| Treatment of mares with estrogen-responsive incontinence | 4-10 micrograms/kg estradiol cypionate IM daily for three days and then every other day | IM | daily then q48h | 3 days then ongoing | 🌎 NA |
- Treatment of mares with estrogen-responsive incontinence: Some mares will improve, but does not 'cure'.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Any | Illegal | — | — | — | 🌎 NA |
- Any: The FDA has stated that the use of ECP in food-producing animals is illegal.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Estradiol cypionate is a long-acting, esterified derivative of the naturally occurring steroidal estrogen, estradiol.
Historically, it was widely used as an abortifacient (mismating shot) in small animals. However, due to the severe and potentially fatal risk of bone marrow suppression (aplastic anemia) and the induction of cystic endometrial hyperplasia/pyometra, most theriogenologists no longer recommend its use in dogs and cats. Safer and more effective alternatives are now preferred.
Clinical Pearl: The FDA has strictly prohibited the use of estradiol cypionate in food-producing animals, making its administration or compounding for such species illegal.
Mechanism of action
Estradiol is the most active endogenous estrogen. It diffuses across the cell membrane and binds to specific intracellular estrogen receptors (ERα and ERβ).
The receptor-hormone complex translocates to the nucleus → binds to estrogen response elements (EREs) on DNA → modulates gene transcription.
Key systemic effects include:
- Reproductive: Stimulates normal growth and development of female sex organs, increases cervical mucosal secretions, thickens vaginal mucosa, and induces endometrial proliferation and uterine tone.
- Skeletal: Increases calcium deposition, accelerates epiphyseal closure, and promotes bone formation.
- Endocrine: Modulates pituitary gonadotropin release, which can inhibit lactation, ovulation, and androgen secretion.
Safety & warnings
Contraindications
- Pregnancy (teratogenic and causes fetal bone marrow depression)
- Food-producing animals (illegal per FDA)
- Ferrets (highly susceptible to severe bone marrow toxicity)
- Estrogen-responsive incontinence in small animals (safer alternatives like DES or estriol should be used)
Adverse effects
- Bone marrow toxicity (thrombocytopenia, leukopenia, fatal aplastic anemia)
- Cystic endometrial hyperplasia
- Pyometra
- Mammary neoplasia
- Feminization (in males)
- Prolonged estrus (in females)
- Genital irritation (cattle)
- Decreased milk flow (cattle)
- Follicular cysts (cattle)
Precautions
Use with extreme caution in small animals due to the high risk of blood dyscrasias (bone marrow depression), which are more prevalent in older animals and at higher dosages. Toxicity can progress to fatal aplastic anemia.
In cows with a prolonged corpus luteum, rule out endometritis or pregnancy before use.
Do not use in ferrets due to extreme sensitivity to estrogen-induced bone marrow toxicity.
Drug interactions
May increase estrogen levels due to CYP450 enzyme inhibition.
Enhanced glucocorticoid effects; estrogens may alter protein binding or decrease metabolism of corticosteroids.
May increase estrogen levels.
May decrease estrogen activity via hepatic enzyme induction.
May decrease estrogen activity via hepatic enzyme induction.
May decrease estrogen activity.
Oral anticoagulant activity may be decreased; dosage adjustments may be necessary.
Monitoring
- Packed Cell Volumes (PCV)
- White blood cell counts (CBC)
- Platelet counts (Baseline, one month after therapy, and repeated two months after cessation if abnormal)
- Liver function tests
Pharmacokinetics
Absorption
Esterified estrogens (like estradiol cypionate) have delayed, prolonged absorption after IM administration in oil solutions.
Distribution
Distributed throughout the body and accumulates in adipose tissue.
Metabolism
Principally metabolized by the liver.
Elimination
Primarily excreted in the urine, but also excreted into the bile where most is reabsorbed from the GI tract (enterohepatic recirculation).
Overdose
Acute overdosage reports in veterinary patients are rare, but chronic or high-dose exposure leads to severe adverse effects.
Overdose manifestations:
- Small Animals: Severe bone marrow depression (thrombocytopenia, leukopenia, aplastic anemia), cystic endometrial hyperplasia, and pyometra.
- Cattle: Prolonged estrus, genital irritation, decreased milk flow, precocious development, and follicular cysts.
Treatment is largely supportive. If bone marrow suppression occurs, aggressive supportive care (transfusions, broad-spectrum antibiotics) is required, though prognosis for aplastic anemia is poor.
Available products
Formulations
- Injection (oil solution)
- Tablets
- Implants (veterinary beef cattle)
Veterinary
- Estradiol-containing implants for use in beef cattle
Human-labeled
- Estradiol Cypionate in Oil for Injection: 5 mg/mL
- Estradiol Valerate in Oil for Injection: 10 mg/mL, 20 mg/mL & 40 mg/mL
- Estradiol Tablets: 0.45 mg, 0.5 mg, 0.9 mg, 1 mg, 1.5 mg, 1.8 mg & 2 mg micronized estradiol
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in light-resistant containers at temperatures of less than 40°C, preferably at room temperature (15-30°C); avoid freezing. Do not mix with other medications.
Client information
- Severe Risk Warning: This medication can cause severe, sometimes fatal, damage to the bone marrow in dogs and cats. It is rarely used today for this reason.
- Contact your veterinarian immediately if your pet shows signs of anemia or bleeding, such as pale gums, unusual bruising, pinpoint red spots on the skin, or extreme lethargy.
- Watch closely for signs of a severe uterine infection (pyometra), which include drinking excessive amounts of water, frequent urination, lethargy, or vaginal discharge. This can occur 1 to 6 weeks after treatment.
- Do not use in pregnant animals, as it causes severe birth defects.
- Illegal in food animals: This drug must never be used in animals intended for human consumption.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.