7 Prometrium (Micronized Progesterone) Side Effects You Should Know About

Prometrium (micronized progesterone) is a lab-made form of the hormone progesterone. You might take it if you’re having irregular menstrual cycles or along with estrogen as part of hormone replacement therapy (HRT) during menopause.

Even though Prometrium works like a natural hormone in the body, it can still cause side effects when you take it. Knowing what side effects to look out for can help you get the most from your medication and alert you to seek medical care when needed.

Prometrium side effects at a glance

Below is a list of common and rare Prometrium side effects to be aware of. Keep in mind that this isn’t a complete list, so it’s a good idea to talk to your healthcare team about any side effects you experience, even if they aren’t listed here.

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Common Prometrium side effects include:

• Headache

• Sore breasts

• Spotting or breakthrough vaginal bleeding

• Dizziness and drowsiness

• Mood changes

• Bloating and fluid retention

• Diarrhea

• Vaginal discharge or dryness

• Muscle or joint pain

• Weight changes

Rare but serious Prometrium side effects include:

• Breast tissue changes

• Vision changes

• Extreme dizziness, drowsiness, or trouble walking

• Liver problems

• Increased risk of blood clots

• Increased blood glucose (sugar)

Prometrium capsules contain peanut oil. You may have a severe allergic reaction to Prometrium if you’re allergic to peanuts.

Prometrium also has a boxed warning, the FDA’s most serious warning, for an increased risk of heart problems, dementia, and breast cancer. These warnings are in reference to taking Prometrium along with estrogen as part of HRT for menopause symptoms. The risk of these side effects varies based on your personal medical history.

Let’s take a closer look at seven Prometrium side effects and what to do if they occur.

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1. Breast changes

Sore or tender breasts are a common Prometrium side effect. You can try home treatments to help with this side effect. These include wearing a well-fitting sports bra, using warm or cool compresses, and taking over-the-counter (OTC) pain relievers.

Less commonly, other breast changes may occur while taking Prometrium. These can include unusual lumps, nipple discharge, or dimpling of the breast tissue. In some cases, these may also be signs of breast cancer. So it’s important to tell your prescriber about any breast changes that occur while you’re taking Prometrium.

Good to know: The Women’s Health Initiative (WHI) study found an increased risk of breast cancer in women taking Premarin (conjugated estrogens) and Provera (medroxyprogesterone) together for HRT. Prometrium is a different form of progesterone, so it doesn’t seem to carry the same breast cancer risks as Provera. But you should still discuss the risks and benefits of HRT with your prescriber before taking Prometrium. 

2. Vaginal discharge or bleeding

Since Prometrium is a hormone, it may cause changes to your menstrual cycle (if you haven’t gone through menopause). You might experience light spotting or breakthrough bleeding while you’re taking it.

Prometrium can also change or increase vaginal discharge, regardless of your age. So it’s a good idea to wear a pantyliner to help protect your clothing until you know how it affects you. Keep in mind that if your vaginal discharge has an unusual color or smell, it could be a sign of an infection. Seek medical treatment if this occurs.

If your vaginal bleeding is severe or you’re bleeding after menopause, let your prescriber know. They can determine if there’s something more serious causing these symptoms.

3. Dizziness and drowsiness

Feeling dizzy or drowsy is common when taking Prometrium. These side effects may improve as your body adjusts to the medication. But it’s a good idea to use caution when driving or performing other activities that require coordination until you know how Prometrium affects you. It’s also recommended that you take it at bedtime to help lessen these side effects during the day.

In rare cases, Prometrium may cause severe dizziness or drowsiness. You may also feel confused or disoriented, as though you are drunk or intoxicated. If this happens, reach out to your healthcare team for guidance.

4. Nausea

Nausea is another common Prometrium side effect. This is because progesterone can slow digestion and make food linger in your stomach. This can lead to feelings of fullness and nausea.

Your nausea may reduce or pass as you continue taking Prometrium. In the meantime, try eating small, frequent meals and choosing bland foods. Spicy, oily, or fried foods can make nausea worse. Some people find that ginger chews or teas also help.

5. Mood changes

Mood changes can happen while you’re taking Prometrium. These changes may include depression, anxiety, or irritability. You may also feel more sensitive or have more trouble controlling your emotions than usual. In most cases, these symptoms are mild. But taking steps to manage your stress, including regular exercise and good sleep hygiene, can help.

In rare cases, Prometrium may cause more severe mood changes, such as aggression or suicidal thoughts. In this case, seek medical care right away.

6. Weight changes

Both weight gain and weight loss can happen while taking Prometrium. But in most cases, weight changes aren’t significant.

Prometrium may cause fluid retention in some people. This means your body may hold on to more fluid than usual, which can leave you feeling bloated and puffy. It may even increase your weight slightly. In most cases, this side effect is mild and goes away on its own. But reducing your salt intake and getting moderate exercise might help.

Excess fluid may be more risky if you also have heart or kidney problems. So be sure to let your prescriber know about your medical history before starting Prometrium. If your fluid buildup is severe or doesn’t get better while you’re taking Prometrium, seek medical care.

7. Liver problems

It’s not common, but liver problems can happen as a side effect of Prometrium. Liver problems are more likely with high doses of progesterone, especially if you’re taking it along with high doses of estrogen or tamoxifen.

Signs and symptoms of liver problems typically appear within a week or two of starting Prometrium and can include:

• Abdominal pain

• Itchy skin

• Yellowing of the eyes or skin (jaundice)

• Fever or chills

• Vomiting

• Diarrhea

Your prescriber will likely measure your liver enzymes to help detect any sign of a liver problem. But if you notice any of the above symptoms, seek medical care.

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Written by:

Jill Barat, PharmD

Jill Barat, PharmD has nearly 10 years of experience as a pharmacist, including serving as the pharmacist in charge at an independent sterile and non-sterile compounding pharmacy. She also worked as the head of medical content for a telemedicine company.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Tegan Smedley, PharmD, APh

Tegan Smedley, PharmD, APh, has 10 years of experience as a pharmacist. She has worked in a variety of settings, including retail, hospital, and ambulatory care.

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