Premarin (Conjugated Estrogens) is one of the most widely prescribed hormone replacement therapy (HRT) medications in the United States. Like all medications, it comes with potential side effects — some mild and temporary, others serious enough to require immediate medical attention.

This guide breaks down exactly what to expect, what's normal, and when you should call your doctor.

What Is Premarin?

Premarin is a conjugated estrogen medication made from a mixture of estrogens derived from pregnant mares' urine. It's manufactured by Pfizer and available as oral tablets, vaginal cream, and injection. It's used primarily to treat menopausal symptoms like hot flashes and vaginal dryness, and to prevent postmenopausal osteoporosis.

To understand how it works in your body, see our guide on how Premarin works.

Common Side Effects

Most people who take Premarin experience some side effects, especially in the first few weeks. These are usually mild and often improve as your body adjusts. Common side effects include:

• Headache — One of the most frequently reported side effects
• Breast tenderness or swelling — Your breasts may feel sore or fuller than usual
• Nausea and stomach cramps — Taking Premarin with food can help
• Bloating — Fluid retention is common, especially early on
• Weight changes — Some women gain a few pounds; others don't notice a change
• Vaginal bleeding or spotting — Irregular bleeding is common in the first few months, especially if you recently stopped having periods
• Hair changes — Some women notice hair loss or increased hair growth
• Dizziness — Usually mild and goes away on its own
• Mood changes — Including irritability or feeling emotional
• Decreased sex drive — May occur in some women

Most of these side effects ease up within the first 2–3 months of treatment. If they don't, or if they're bothering you, talk to your doctor. Sometimes a dose adjustment is all it takes.

Serious Side Effects

Premarin carries a boxed warning (the FDA's most serious warning label) for several conditions. While rare, these are serious and require immediate medical attention.

Blood Clots

Premarin increases the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE). Symptoms to watch for:

• Sudden leg pain, swelling, or warmth (especially in one leg)
• Sudden shortness of breath or chest pain
• Coughing up blood

Call 911 immediately if you experience any of these symptoms.

Stroke

The Women's Health Initiative (WHI) study found an increased risk of stroke in women taking estrogen-alone therapy. Watch for:

• Sudden numbness or weakness on one side of the body
• Sudden confusion, trouble speaking, or difficulty understanding speech
• Sudden severe headache with no known cause
• Sudden trouble seeing or walking

Heart Attack

Women taking estrogen-progestin combinations (like Prempro) had a higher risk of heart attack in the WHI study. Symptoms include:

• Chest pain or pressure
• Pain spreading to your jaw, neck, or arm
• Shortness of breath, nausea, or cold sweats

Breast Cancer

Long-term use of estrogen-progestin therapy is associated with an increased risk of breast cancer. If you take Premarin with a progestin, report any breast lumps, nipple discharge, or changes in your mammogram to your doctor promptly.

Endometrial Cancer

Taking estrogen without a progestin significantly increases the risk of endometrial (uterine) cancer in women who still have a uterus. This is why doctors prescribe a progestin alongside Premarin for these patients. Report any unusual vaginal bleeding right away.

Other Serious Side Effects

• Gallbladder disease — Pain in your upper right abdomen, especially after eating
• Liver problems — Yellowing of skin or eyes (jaundice), dark urine
• Severe allergic reactions — Difficulty breathing, swelling of face/throat, hives
• Vision changes or loss — Sudden blurred vision, bulging eyes, or double vision
• Probable dementia — In women 65 and older, estrogen therapy may increase the risk of dementia

Specific Populations

Women Over 65

The WHI study found that women 65 and older taking estrogen (alone or with progestin) had an increased risk of probable dementia. If you're in this age group, discuss the risks and benefits carefully with your doctor.

Women With a Uterus

If you still have your uterus, your doctor should prescribe a progestin alongside Premarin to reduce the risk of endometrial cancer. Never take Premarin alone if you have a uterus unless specifically directed by your doctor.

Pregnancy and Breastfeeding

Premarin is Category X — it should absolutely not be used during pregnancy. It also passes into breast milk and may reduce milk production, so it's not recommended during breastfeeding.

How to Manage Common Side Effects

Here are practical tips for dealing with the more common side effects:

• Nausea: Take Premarin with food or at bedtime
• Headaches: Stay hydrated and keep a consistent schedule. If headaches are severe or persistent, tell your doctor
• Bloating: Reduce salt intake and stay active. Bloating usually improves after the first month or two
• Breast tenderness: Wear a supportive bra and avoid caffeine. This often improves over time
• Spotting: Irregular bleeding in the first 3 months is common. If it persists beyond 3 months or is heavy, contact your doctor
• Mood changes: If mood swings are significant, a dose adjustment may help

The general rule: use the lowest effective dose for the shortest time needed. This minimizes your risk of serious side effects while still treating your symptoms.

When to Call Your Doctor

Contact your doctor if you experience:

• Side effects that don't improve after 2–3 months
• Unusual vaginal bleeding (especially heavy or prolonged)
• Breast lumps or changes
• Persistent headaches or migraines
• Mood changes that affect your daily life

Call 911 or go to the ER immediately if you have:

• Signs of a blood clot (leg swelling, sudden chest pain, shortness of breath)
• Signs of a stroke (sudden numbness, confusion, trouble speaking)
• Signs of a heart attack (chest pressure, pain radiating to arm/jaw)
• Sudden vision changes or loss
• Severe allergic reaction (swelling, difficulty breathing)

Final Thoughts

Premarin is an effective treatment for menopause symptoms, but it's important to understand both the common and serious side effects. Most women tolerate it well, especially at lower doses. The key is to stay informed, communicate with your doctor, and report any concerning symptoms promptly.

If you're considering Premarin, check out our guides on what Premarin is and how it's used, drug interactions to watch for, and how to save money on your prescription.

Ready to fill your prescription? Find Premarin in stock near you on Medfinder.