Conjugated Estrogens (Premarin)
A mixture of estrogen sulfate salts (chiefly estrone sulfate and equilin sulfate) derived from pregnant mares' urine. A long-standing menopausal HRT and one of the most-studied estrogen products, central to the Women's Health Initiative trials.
01 Overview
Conjugated equine estrogens (CEE) are a blend of sulfated estrogens including sodium estrone sulfate and equilin sulfate. Marketed as Premarin since the 1940s, it is used for menopausal vasomotor symptoms, vulvovaginal atrophy and osteoporosis prevention, and historically in feminizing therapy.
CEE was the estrogen used in the landmark Women's Health Initiative trials, which reshaped understanding of HRT risks and benefits. Because it contains equine estrogens not native to humans and cannot be tracked by standard estradiol assays, many clinicians now prefer bioidentical estradiol for feminization.
02 Mechanism
Sulfated estrogens are hydrolysed to active estrogens (estrone, equilin and derivatives) that agonise estrogen receptors, relieving menopausal symptoms and suppressing gonadotropins.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Menopausal HRT | 0.3–1.25 mg/day | Oral | 0.3-0.625 mg typical for vasomotor symptoms. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Relief of vasomotor symptomsReduces hot flushes and night sweats of menopause. | Clinical | ||
| Bone density preservationReduces postmenopausal bone loss and fracture risk. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Venous thromboembolism and strokeWHI showed increased VTE and ischaemic stroke, especially with older age at initiation. | Life-threatening | Uncommon | Clinical | |
| Endometrial hyperplasiaUnopposed estrogen in a person with a uterus raises endometrial cancer risk. | Moderate | Common if unopposed | Clinical |