Hormone Replacement Therapy: The Tragedy of Premarin

Each year, thousands of horses are impregnated and then confined to cramped stalls so that their estrogen-rich urine can be collected and used by pharmaceutical companies to make the drug Premarin for hormone replacement therapy (HRT). But the cruelty involved in Premarin production is not the only tragedy—the dangers of long-term HRT have been hidden, because researchers have relied on misleading animal tests. As a result, millions of women have been put at risk of contracting breast cancer and of having a heart attack or stroke.


For most of their 11-month pregnancies, the mares used in Premarin production are confined to stalls so small that the animals cannot turn around or take more than one step in any direction. The mares are forced to wear rubber urine-collection bags at all times, which causes chafing and lesions, and their drinking water is limited so that their urine will yield more concentrated estrogen. When they finally give birth, their babies are taken away from them within days and they are quickly impregnated again. This cycle continues year after year until the mares become old, infertile, or crippled, at which point they are auctioned off for slaughter.


Because the Premarin-production industry keeps mares constantly impregnated in order to maintain high estrogen levels in their urine, thousands of foals are born each year—animals the industry considers to be mere byproducts. While some of the female babies are raised to replace their broken-down mothers, most will be slaughtered and sold for their flesh in Europe and Japan.

The Dangers of Taking Premarin

In 2002, researchers who were working on the Women’s Health Initiative (WHI)—a series of government studies of more than 160,000 healthy postmenopausal women—abruptly halted a trial involving 16,000 women who were taking Premarin when it was found that HRT raises the risk of stroke in women by 41 percent, the risk of heart attack by 29 percent, and the risk of breast cancer by 26 percent. Doctors now largely agree that most women should avoid HRT and recommend that those who must use it in order to relieve severe symptoms associated with menopause limit the duration of the treatment, use the lowest effective dose, and use plant-derived estrogen, which uses soy or yam extracts instead of horse urine. These plant-based hormones, which are “bioidentical” to human hormones, have fewer side effects in humans than horse-urine-based hormones do.

Animal Experiments Cost Women’s Lives

The WHI findings contradicted the results of years of animal experiments that suggested that estrogen and progestin protect women from heart attacks and strokes. The HRT animal “models” were fundamentally misleading, because a 3-month-old rat whose ovaries have been removed (the standard post-menopausal “model”) is not the same as a 50-year-old human female who is going through a natural life phase. Wyeth relied heavily on these animal tests in promoting long-term Premarin use for all menopausal women and, as a result, put millions of women at risk.

What You Can Do

If possible, avoid hormone replacement therapy. Many women find that they can control hot flashes and other symptoms associated with menopause by making easy lifestyle changes, such as switching to a low-fat vegetarian or vegan diet and adding regular exercise.

If you are currently seeking hormone replacement therapy, ask your physician to prescribe one of the many safe and effective plant-based alternatives that are available.

If your veterinarian prescribes Premarin to dogs who are suffering from incontinence, suggest a switch to a more humane alternative, such as diethystillbestrol (DES) or phenylpropanolamine.

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