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What is Premarin®?

Tricia Christensen
Updated May 17, 2024
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Premarin® is a medication that may be available in pill or cream form, and contains several types of estrogens. The company Pfizer manufactures this brand-name drug, but there are generic forms and a few other companies that synthesize this medicine from the collected urine of pregnant horses. A number of animal rights groups are opposed to collection methods and housing of mares used to create the medication, and the overall use of Premarin® has declined in recent years. This is not so much due to ethical objections, but more resulting from concerns about risks of using hormone replacement therapy.

The most common reasons to prescribe Premarin® are to alleviate symptoms associated with menopause. These include strong symptoms of vaginal dryness, mood changes, hot flashes, and others. In particular, the medicine may be recommended if women have total hysterectomies long before they would ordinarily experience menopause. In these cases, the medication or other hormone replacement therapies (HRT) could be recommended. Some women also take the drug during onset or after normal menopause when symptoms of declining estrogen become severe.

Dosage of this medicine in pill form is similar to the way birth control pills are dispensed. People may take it for a little over three weeks and then take a break of five days before starting it again. Cyclical dosing isn’t always used, and the dose dispensed depends on a patient’s medical condition.

Important warnings about hormone replacement therapy apply to drugs like Premarin®. HRT elevates the risk for certain cancers of the breast and reproductive tract. It may be associated with higher risk for heart disease and blood clot disorders like stroke. People with family history of these cancers or elevated heart disease or stroke risk should not use this medicine. Those who do need to be especially vigilant in performing breast self-exams, and should report any changes or lumps felt to doctors.

Some side effects may occur with Premarin®. Women might note increase in body hair, nausea, headaches, and weight loss or gain. The breasts may become swollen or tender, libido may decrease, and women may have an increase in vaginal discharge. Other effects may include bloating in the stomach or cramping.

More severe adverse effects include jaundice or yellowing the skin and the whites of the eyes, which may indicate liver problems. Allergic reactions with hives, difficulty breathing and swelling of the face occasionally occur and is medically urgent. Severe migraines, very heavy menstrual bleeding, a sense of confusion or any suggestion of heart attack or stroke are indications to get medical help immediately.

Many drugs interact with Premarin®, including some antidepressants, some mood stabilizers, blood thinners, seizure drugs and certain forms of drugs for diabetes. It’s important to bring a full list of medications, including any herbal supplements or over the counter drugs, to the doctor’s so these can be evaluated before a prescription is given. Knowing personal and family medical history is also valuable in determining whether drugs like Premarin® are appropriate.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Tricia Christensen
By Tricia Christensen , Writer
With a Literature degree from Sonoma State University and years of experience as a WiseGeek contributor, Tricia Christensen is based in Northern California and brings a wealth of knowledge and passion to her writing. Her wide-ranging interests include reading, writing, medicine, art, film, history, politics, ethics, and religion, all of which she incorporates into her informative articles. Tricia is currently working on her first novel.

Discussion Comments

By anon996053 — On Jul 02, 2016

These mares stand for months at a time with a bag hanging off their tail to collect the urine. They are also kept pregnant over and over again because the urine has to come from pregnant mares. They supposedly get a month "off" to walk at will in a pasture or corral.

Gestation in horses is eleven to twelve months and this is how long the mares have to stay in their stall. Hundreds of horses are kept in each barn and then, what happens to all those foals that are born?

These animals are abused in the way that the pigs are at the factory farms. Confined to a crate for years. Please don't buy anything that is made with premarin.

Tricia Christensen

Tricia Christensen


With a Literature degree from Sonoma State University and years of experience as a WiseGeek contributor, Tricia...
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