Prometrium is a brand name medication for a type of progesterone. Progesterone is a hormone that’s produced in a woman’s 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 womb. 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 are 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 that you take by mouth once a day. Your doctor may recommend that you take Prometrium at bedtime because 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 for 12 days in a row.

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

The most common side effects from Prometrium include:

  • fatigue
  • headache
  • dizziness
  • bloating
  • nausea or vomiting
  • diarrhea
  • breast tenderness
  • mood swings or depression
  • joint pain
  • problems urinating
  • unusual vaginal discharge
  • swelling of the hands and feet
  • constipation
  • dark patches on the skin, known as melasma
  • spotting in between periods

The combination of estrogen plus Prometrium has been linked to an increased risk for blood clots that could lead to:

You’re more likely to get a blood clot while taking Prometrium if you’re already at risk for clots because you:

  • have diabetes or lupus
  • have high blood pressure or cholesterol
  • have had blood clots in the past
  • are obese
  • smoke

Talk to your doctor about things you can do to protect your heart and reduce your risk for blood clots, such as:

  • maintaining a healthy diet
  • exercising regularly
  • losing weight if you are overweight or obese
  • taking additional medication

Using estrogen and progesterone might increase your chance of getting breast or ovarian cancer. The longer you use these hormones, the greater your risk becomes. Research suggests Prometrium could also increase your risk for dementia.

If you take Prometrium:

  • get annual breast checkups
  • perform breast self-exams at home
  • ask your doctor how often you should get mammograms and Pap smears based on your age and cancer risk

Learn more: Health tests every woman needs »

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 your mouth, tongue, or throat
  • rash
  • trouble breathing

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

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. Go over every drug you use, including herbal supplements and over-the-counter drugs you take.

You should not take Prometrium if you have any of these conditions:

  • abnormal or unusual bleeding from the vagina that hasn’t been diagnosed
  • a peanut allergy (Prometrium contains peanut oil)
  • an allergy to progesterone or any other ingredient in the capsules
  • blood clots in the legs (deep vein thrombosis), lungs (pulmonary embolism), brain, eyes, or other part of your body
  • a history of breast cancer or other reproductive (uterine, cervical, ovarian) cancer
  • leftover tissue in your uterus from a past miscarriage
  • liver disease
  • stroke or heart attack within the past year

You should also avoid Prometrium if you are, or think you might be pregnant. This drug is also not recommended while you are breast-feeding because it can get into breast milk.

Because Prometrium can increase your risk for 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 on 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 will need special monitoring while on Prometrium:

  • asthma
  • diabetes
  • endometriosis
  • epilepsy
  • heart problems
  • high levels of calcium in your blood
  • liver, thyroid, or kidney disease
  • lupus
  • migraine headaches

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

  • Crinone (progesterone gel)
  • Endometrin (vaginal insert)
  • Progest (cream)
  • Prochieve (gel)

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

Because of the risk for cancer or a blood clot, you want to 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.