What You Should Know About Prometrium Side Effects

If your doctor has prescribed Prometrium (Micronized Progesterone), it's normal to wonder about side effects. Like all medications, Prometrium can cause unwanted effects — some mild and temporary, others more serious. Knowing what to expect helps you stay prepared and know when to seek medical attention.

This guide covers the most common side effects, the serious ones to watch for, and practical tips for managing them.

What Is Prometrium?

Prometrium is a brand-name prescription medication that contains micronized progesterone — a bioidentical hormone that matches the progesterone your body naturally produces. It's most commonly prescribed to prevent endometrial hyperplasia in postmenopausal women taking estrogen, and to treat secondary amenorrhea (missed periods).

Prometrium comes as an oral capsule in 100 mg and 200 mg strengths. It's usually taken at bedtime because one of its most common effects is drowsiness.

Common Side Effects of Prometrium

The following side effects are reported frequently in clinical trials. Most are mild and tend to improve as your body adjusts to the medication:

• Drowsiness or sleepiness (27%) — This is one of the most common effects. Taking Prometrium at bedtime can actually help if you have trouble sleeping.
• Headache (31%) — Mild to moderate headaches are common, especially in the first few weeks.
• Dizziness (24%) — You may feel lightheaded, especially when standing up quickly.
• Breast tenderness — Some swelling or sensitivity in the breasts is normal.
• Abdominal pain or bloating — Mild stomach discomfort is common.
• Nausea — Taking Prometrium with food can help reduce this.
• Mood changes or irritability — Hormonal shifts can affect your mood, especially early on.
• Vaginal discharge or spotting — Light spotting is normal, particularly in the first cycle.
• Joint pain — Some women report mild aches in their joints.
• Fatigue — General tiredness beyond just drowsiness.

Most of these side effects are manageable and decrease within the first one to two months. If any of them become severe or persistent, talk to your doctor.

Serious Side Effects: When to Call Your Doctor

While rare, some side effects of Prometrium require immediate medical attention. Contact your doctor or go to the emergency room if you experience:

• Signs of blood clots — Sudden swelling, pain, or warmth in one leg (deep vein thrombosis), chest pain, or sudden shortness of breath (pulmonary embolism).
• Stroke symptoms — Sudden numbness or weakness on one side of the body, difficulty speaking, sudden severe headache, or vision changes.
• Heart attack symptoms — Chest pain or pressure, pain spreading to the arm or jaw, nausea with sweating.
• Vision changes — Sudden partial or complete loss of vision, which could indicate retinal thrombosis.
• Severe allergic reaction — Hives, swelling of the face or throat, difficulty breathing. Note: Prometrium capsules contain peanut oil, so this is especially important if you have a peanut allergy.
• Liver problems — Yellowing of the skin or eyes (jaundice), dark urine, severe abdominal pain.
• Severe depression — New or worsening depression, mood changes that interfere with daily life.

Prometrium carries an FDA boxed warning about increased risks of blood clots, stroke, heart attack, breast cancer, and probable dementia when used with estrogen in postmenopausal women. These risks are generally associated with long-term use.

Side Effects in Specific Populations

Women Over 65

The Women's Health Initiative Memory Study (WHIMS) found an increased risk of probable dementia in women 65 and older taking estrogen plus a progestin. If you're in this age group, your doctor should regularly reassess whether the benefits of Prometrium outweigh the risks.

Pregnant Women

While Prometrium is sometimes used off-label for luteal phase support in early pregnancy under close medical supervision, it is not FDA-approved for use during pregnancy for its labeled indications. Always follow your doctor's guidance.

Women with Peanut Allergies

Prometrium capsules contain peanut oil. If you have a known peanut allergy, you should not take Prometrium. Your doctor can prescribe an alternative progesterone formulation that doesn't contain peanut oil.

Women with Liver Conditions

Prometrium is processed by the liver. If you have liver disease or impaired liver function, your doctor may need to adjust your dose or choose a different medication.

How to Manage Common Side Effects

Here are some practical tips for dealing with the most frequent Prometrium side effects:

• Drowsiness — Take your dose at bedtime. Avoid driving or operating machinery until you know how it affects you.
• Nausea — Take Prometrium with food or a small snack. This also helps your body absorb the medication better.
• Headaches — Over-the-counter pain relievers like acetaminophen (Tylenol) can help. Stay hydrated.
• Dizziness — Stand up slowly from sitting or lying positions. Avoid alcohol, which can make dizziness worse.
• Breast tenderness — Wear a supportive bra. This usually improves after a few weeks.
• Mood changes — Keep a mood journal so you can share patterns with your doctor. Regular exercise and sleep can also help stabilize mood.
• Bloating — Reduce salt intake and drink plenty of water.

If side effects don't improve after two to three months, or if they significantly affect your quality of life, talk to your doctor about adjusting your dose or switching to a different progesterone formulation.

Final Thoughts

Most people who take Prometrium experience only mild side effects that improve over time. The most common — drowsiness, headache, and dizziness — can usually be managed by taking the medication at bedtime and with food.

However, the serious risks (blood clots, stroke, heart attack) are real, especially with long-term use alongside estrogen. That's why it's important to use Prometrium at the lowest effective dose for the shortest time needed.

If you're currently taking Prometrium and need help finding it at a pharmacy, Medfinder can help you check stock availability near you without calling around. And if cost is a concern, check out our guide on saving money on Prometrium.