What Is Progesterone?

Sometimes called the "pregnancy hormone," progesterone plays an important role in fertility and pregnancy.

Progesterone is a natural hormone produced by a woman's ovaries after she ovulates (the moment when an egg is released into the fallopian tube).

The corpus luteum, a temporary endocrine gland, secretes progesterone. (1)

Progesterone: The Pregnancy Hormone

Progesterone is sometimes called the "pregnancy hormone" because of the role it plays in getting pregnant and maintaining a pregnancy. Progesterone gets the uterus ready to accept and maintain a fertilized egg.

When a woman has her menstrual period, her progesterone level is usually low during the first few days.

But once she ovulates, her progesterone level goes up for about five days, then comes back down.

Progesterone Levels, Fertility, and Pregnancy

Progesterone is necessary for pregnancy because it gets the uterus ready to accept, implant, and maintain a fertilized egg. The hormone prevents muscle contractions from happening in the uterus that would cause a woman's body to reject an egg.

If you become pregnant, the hormone helps create an environment that nurtures the developing baby.

Your progesterone level will slowly increase between your 9th and 32nd weeks of pregnancy. (2)

The Role of the Placenta in Progesterone Production

The placenta (the structure inside the uterus that provides oxygen and nutrients to a developing baby) will begin to produce progesterone after 8 to 10 weeks of pregnancy to help maintain a healthy environment for the baby. At this point, the placenta increases progesterone production to a higher rate than your ovaries were producing. These high levels of progesterone throughout your pregnancy cause the body to stop producing more eggs, as well as prepare your breasts to produce milk. (3)

Fertility Problems and Progesterone Tests

If you're having a hard time getting pregnant, your doctor may recommend a blood test for progesterone to see if you're ovulating or if your ovaries are healthy.

If your progesterone level is low but you are pregnant, your doctor may recommend a blood test to check whether your pregnancy is at risk for complications, such as miscarriage or preterm delivery. (2)

Signs and symptoms that indicate you may have a low progesterone level include the following: (1)

• Uterine bleeding
• Missing your periods or having abnormal periods
• Spotting and pain while pregnant
• Repeated miscarriages

Not having enough progesterone can also cause you to have too much estrogen. A high level of estrogen can decrease your sexual desire, cause weight gain, and affect your gallbladder.

Progesterone as a Medication and Treatment

Progesterone is part of a class of medications called progestins.

If you're having trouble getting pregnant, or if you're undergoing fertility treatments, your doctor may recommend that you take progesterone hormone therapy. (4)

This can be done for any of the following reasons:

• To bring on menstruation
• Because your ovaries don't produce enough progesterone
• Because medications you take are lowering your progesterone level
• To replace progesterone that's removed from your ovaries by certain procedures

There are several different forms of progesterone available, so talk to your doctor about which form is best for you.

Progesterone Treatment Delivery Systems

Progesterone treatments come in the following forms:

• Vaginal gel that's usually used once per day
• Vaginal suppository, which can be compounded at specialty pharmacies but is not approved by the Food and Drug Administration (FDA)
• Vaginal inserts, which the FDA has approved for progesterone supplementation, not replacement
• Oral capsule that's inserted vaginally (not approved by the FDA)
• Injection, the most commonly used method, which requires daily injections in the butt

Progesterone and Hormone Therapy or Hormone Replacement Therapy 

Progesterone is also sometimes taken as part of hormone replacement therapy (HRT) in women who have gone through menopause but who haven't had a hysterectomy (surgical removal of the uterus). (4)

Hormone therapy (HT) usually includes taking estrogen to treat menopausal symptoms and reduce the risk of developing certain diseases.

Note that taking progesterone can cause side effects, including the following:

• Headaches
• Breast tenderness or pain
• Vomiting
• Diarrhea
• Constipation
• Tiredness
• Mood swings
• Irritability
• Sneezing
• Coughing
• Vaginal discharge

Taking progesterone can also cause more serious side effects, such as the following:

• Breast lumps
• Migraines
• Dizziness and faintness
• Impaired speech
• Seizures
• Numbness in the arms or legs
• Swelling or pain in the legs
• Balance issues
• Difficulty breathing
• Accelerated heartbeat
• Chest pain
• Vision issues
• Uncontrollable shaking in the hands
• Stomachaches
• Itchy skin or rash
• Vaginal bleeding
• Depression

If you experience any of these serious side effects, call your doctor.

Controversy Around Hormone Therapy

In the early 2000s, people began worrying about the risks of hormone therapy. At the time, a Women’s Health Initiative (WHI) study showed that there was a link between combined estrogen and progestin therapy and an increased risk of breast cancer and cardiovascular disease. The study also appeared to show that hormone therapy was more harmful to postmenopausal women than it was helpful, stating that estrogen alone appeared to be related to an increased risk of stroke, as well as not helpful for coronary artery disease. (5, 6)

The WHI published the results of the study in JAMA, announcing that, despite following participants for a mean of five years, study investigators had ceased the estrogen-plus-progestin portion of the study before its original stop date. The reason for the sudden end was that it was deemed unethical to continue the study because the WHI had discovered an excess risk of breast cancer in women taking the drugs. (6,7)

Then two years after the announcement, the WHI also ended the estrogen-only study before it was complete, stating that it found an increased risk of blood clots in women taking the medication. However, these women didn't face a significant increase in breast cancer risk. (6,7)

With that said, more current analyses do not show these risks to be apparent with hormone therapy. Consider a follow-up study published in September 2017 in JAMA, which reported that neither estrogen plus progestin taken for a median of 5.6 years nor estrogen alone taken for a median of 7.2 years were associated with an increased risk of death due to all causes, cardiovascular issues, or cancer during a cumulative follow-up of 18 years. (8)

While there are different thoughts on hormone therapy, your doctor can help determine if it is an appropriate treatment for you.

Progesterone for Birth Control and Contraception

Progesterone can also help you avoid getting pregnant.

A form of progesterone, called progestin, is used in combination with estrogen in hormonal contraception such as birth control pills, vaginal rings, and the skin patch.

Progesterone is also used as birth control by itself in pill and injection form. Other types of progestin-only birth control include the birth control implant and hormonal intrauterine device (IUD). (9)

These forms of birth control protect women against pregnancy due to the following actions: (9)

• Causing the mucus in the cervix to thicken, which makes it hard for sperm to reach the uterus and fertilize an egg
• Stopping ovulation
• Thinning the lining of the uterus

Talk with your doctor about which method is best for you.

Progestin-Only Birth Control Pills

Also called “mini-pills," these may cause the following side effects:

• Headaches
• Nausea
• Breast tenderness
• Inconsistent bleeding, such as not bleeding at all, short cycles of bleeding, spotting, or heavy bleeding

Women with lupus or those who have a personal history of breast cancer should not take this form of birth control.

Vaginal Rings

Sold as NuvaRing, and coming to market as Annovera, this small ring is inserted into your vagina. NuvaRing contains estrogen and progestin. (10) Annovera is lined with segesterone acetate, a new form of progestin, and ethinyl estradiol, or estrogen.

The ring needs to be replaced every month, and if you go without it inside your vagina for more than 48 hours during the weeks you should be wearing it, you're not fully protected from getting pregnant.

If you take any of the following, NuvaRing may not be as effective:

• Antibiotics such as Rifadin (rifampin)
• Grifulvin (griseofulvin), an antifungal
• Some HIV medications
• Some antiseizure and mental health medications
• Saint-John’s-wort

Possible side effects of NuvaRing may include these conditions:

• Back and jaw pain
• Stomach pain
• Nausea, sweating, and breathing difficulties
• Chest pain or discomfort
• Intense headaches
• Vision problems, such as seeing flashes
• Yellowing of the skin or eyes

Progesterone Patches

The birth control skin patch works like other forms of hormonal birth control in that it contains estrogen and progestin.

The patch is worn on your belly, upper arm, butt, or back, and it is replaced every week for three weeks. Then you don't wear the patch for a week and repeat the cycle. (11)

If you take any of the medication or supplements listed as potentially problematic with a vaginal ring, the patch may be less effective as well.

Additionally, using the patch can cause the same side effects as NuvaRing.

Progesterone Shots or Injections

The birth control injection (also known as the birth control shot) is available as the brand Depo-Provera. It consists of depot medroxyprogesterone acetate and prevents pregnancy for three months.

A healthcare provider has to give you the injection. When you get your first shot, you can be anywhere in your menstrual cycle. After that time, you need to get an injection every 13 weeks, with 15 weeks being the latest you can receive it for it to be effective. If you get the injection more than 15 weeks from the last one, use other methods to avoid getting pregnant for the next seven days, such as abstaining from sexual intercourse or using condoms. (12)

Bonus Benefits From the Birth Control Shot

In addition to birth control, the injection may provide the following health benefits:

• Cause your period to stop
• Reduce the risk of uterine cancer
• Protect against pelvic inflammatory disease
• Relieve pain from endometriosis
• Help relieve symptoms of sickle cell disease and seizure disorders
• Reduce bleeding associated with uterine fibroids

The injection can also cause the following side effects:

• Irregular bleeding
• Weight gain (less than 5 pounds)
• Delay in getting pregnant after you stop the injection (takes an average of 10 months)
• Bone loss (some of the bone loss is regained when you stop the injections)

Call your doctor if you experience any of these side effects.

Also, if you are at risk for cardiovascular disease or have a history of stroke, vascular disease, or uncontrolled high blood pressure, talk with your doctor about whether the injection is a safe choice for you. Taking the injection can increase the risk of cardiovascular disease during and after you stop taking it. (12)

Contraceptive Implants

These arm implants provide long-term birth control via a small flexible plastic rod that is placed under the skin of your upper arm. The rod releases progestin. (13)

Having any of the following may not make you a good candidate for an implant:

• Allergies to the materials in the implant
• History of blood clots, heart attack, or stroke
• Liver tumors or liver disease
• History of breast cancer
• Undiagnosed abnormal genital bleeding

Hormonal IUD 

This type of birth control contains hormones that work in the same way as other forms of birth control. However, the IUD is a small flexible plastic frame that's inserted into your uterus. IUDs that incorporate progestin are known by the brand names Mirena, Kyleena, Liletta, and Skyla. These IUDs can be inserted for three to six years. They can also make your period lighter or disappear altogether. (14)

Possible side effects of hormonal IUDs include the following:

• The device may slip out of your uterus or out of place.
• You may get an infection if bacteria reaches the uterus when it's inserted.
• The device may push through the wall of the uterus, requiring it to be surgically removed (this is rare)

Another kind of IUD that doesn't release hormones is called a copper IUD or Paragard.