Prometrium is a brand-name medication for a type of progesterone known as micronized progesterone. Progesterone is a hormone that’s produced in the ovaries. Progesterone prepares the lining of the uterus to protect and nourish a growing baby during pregnancy.

Progesterone also helps control your menstrual cycle. Each month you don’t become pregnant, your progesterone levels drop and you get your period.

During pregnancy, the placenta also produces progesterone. The placenta is the organ that nourishes a growing baby in the uterus. That extra progesterone stops your body from ovulating while you’re pregnant.

If your progesterone levels dip too low, you won’t get your normal periods. During the transition to menopause, levels of progesterone and another hormone, estrogen, rise and fall. These changing hormone levels can lead to hot flashes and other symptoms.

After menopause, your ovaries will stop producing both progesterone and estrogen.

If your body no longer makes enough or any progesterone, you can take Prometrium to replace it. Your doctor might prescribe Prometrium if your periods have stopped for several months (amenorrhea).

A few things can cause your progesterone levels to drop and your periods to stop. These include:

  • a medicine you take
  • a hormone imbalance
  • a very low body weight

Prometrium can help restore your progesterone levels and restart your normal periods.

You doctor may also prescribe Prometrium if you went through menopause and you’re taking estrogen hormone replacement therapy to treat symptoms like hot flashes.

Estrogen alone can increase your risk for uterine cancer. Adding Prometrium to your hormone therapy treatment lowers your uterine cancer risk back to normal.

Prometrium is a capsule you take by mouth once a day. Your doctor may recommend you take Prometrium at bedtime, as it can sometimes cause dizziness.

If you use Prometrium to prevent uterine cancer while you’re on estrogen hormone replacement therapy, you’ll take 200 milligrams daily for 12 days in a row.

If you use Prometrium to restart your period, you’ll take 400 milligrams daily for 10 days.

The most common side effects of Prometrium (in order) include:

  • headache
  • breast tenderness
  • joint or muscle pain
  • depressed mood
  • irritability
  • dizziness
  • bloating
  • hot flashes
  • problems urinating
  • vaginal discharge
  • nausea and vomiting
  • diarrhea
  • chest pain
  • fatigue
  • night sweats
  • swelling of hands and feet
  • vaginal dryness

Several safety concerns have been raised related to the use of estrogen and progesterone, including and increased risk of:

  • blood clots
  • stroke
  • heart attack
  • breast cancer
  • dementia

These concerns are based on older studies that used estrogen and a synthetic progesterone called medroxyprogesterone.

Prometrium is a natural form of progesterone. It’s identical to the progesterone produced by the body.

According to 2017 guidelines from the American Association of Clinical Endocrinologists and the American College of Endocrinology, Prometrium may be less likely to cause breast cancer than synthetic progesterone. However, more studies are needed to understand the long-term safety of these drugs.

A small number of people may feel dizzy, drowsy, or confused while taking Prometrium. Be careful about driving a car or operating machinery until you know how you react.

Allergic reaction

Allergic reactions to Prometrium are rare, but they can happen. Call your doctor right away if you have any of these symptoms:

  • swelling of the mouth, tongue, or throat
  • rash
  • trouble breathing

Prometrium capsules contain peanut oil. Don’t take them if you’re allergic to peanuts.

Discuss all the possible risks and benefits of taking Prometrium with your doctor. Let your doctor know about any allergies you have to medicine or food. Also tell your doctor if you have a family history of cancer.

Be sure to go over every drug you use, including herbal supplements and over-the-counter drugs you take.

You shouldn’t take Prometrium if you have any of these conditions:

Also avoid Prometrium if you are or think you might be pregnant. This drug is also not recommended while you’re breastfeeding.

Because there are concerns that progesterone might increase the risk of blood clots, let your doctor know if you plan to have surgery. You might have to stop taking the drug for about four to six weeks before your procedure.

Don’t smoke while you’re using this drug. Smoking can further increase your risk for a blood clot.

Also, let your doctor know if you have any of these conditions, because you’ll need special monitoring while on Prometrium:

Other progesterone medications are available in gel or cream form. These include:

  • Crinone (progesterone gel)
  • Endometrin (vaginal insert)
  • Pro-Gest (cream)

Talk to your doctor about whether Prometrium or one of these products might be your best option.

You should take Prometrium for the shortest length of time, and in the smallest dose, needed to treat your condition.

If you take combination hormone replacement therapy, see your doctor every three to six months to make sure you still need Prometrium. Also get regular physical exams to check your heart and overall health.