What Is Progesterone?

Medically Reviewed By Sanaz Ghazal, MD, FACOG
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Progesterone is a hormone that the human body naturally produces. It is related to reproduction.

Sex and gender disclaimer

Sex and gender exist on spectrums. This article uses the terms “female” and “male” to refer to sex assigned at birth. 

Learn more about the differences between sex and gender here.

Progesterone is a hormone involved in reproduction. It is best known for the role it plays in the female body after puberty. It helps regulate menstruation, sustain a pregnancy, and develop an embryo.

In the male body, progesterone contributes to sperm function.

This article further defines progesterone. It also covers its uses and discusses what it means if you have atypical levels of the hormone.

What is progesterone?

Female from a low angle with a tree in the background
Mengwen Cao/Getty Images

After puberty and until menopause, a female’s body produces progesterone monthly. Progesterone is produced mainly in the ovaries. A small amount of progesterone is produced in the adrenal glands, which are located slightly above the kidneys. If a female becomes pregnant, at around week 10, the developing placenta takes over the production of progesterone that maintains the pregnancy.

In males, progesterone is produced in the adrenal glands and the testes.

What is the function of progesterone?

In females, the main roles of progesterone are to regulate the menstrual cycle and maintain a pregnancy.

During the menstrual cycle, progesterone prepares the body for pregnancy. Progesterone production begins with ovulation when a single egg is released from your ovaries.

Once the egg is released, the empty ovarian follicle morphs into an endocrine, or hormone-producing, gland called a corpus luteum. The corpus luteum produces sufficient progesterone to maintain a pregnancy immediately after fertilization and when the fertilized egg implants in the endometrium, which is the lining of your uterus.

During pregnancy, progesterone maintains the pregnancy by helping develop blood vessels in the endometrium. It stimulates glands in this lining to secrete nutrients that nourish the fertilized egg. In addition, rising progesterone and estrogen levels lead to breast changes, including an increase in the number and size of the milk ducts.

As the fertilized egg develops, the placenta grows. It begins to secrete progesterone and becomes the main source of progesterone in your body. These high levels of progesterone stop additional eggs in your ovaries from maturing.

Immediately after giving birth, the levels of progesterone and estrogen fall quickly. At the same time, there is a surge in prolactin and oxytocin levels. These hormones help with the production of breast milk so that you can start nursing the baby.

As you approach menopause, hormone levels in your body begin to drop. You become less likely to ovulate and produce less progesterone. This leads to longer or missed menstrual cycles and other effects associated with menopause.

In males, progesterone is produced in the adrenal glands. Its role is associated with sperm function, including the movement of the sperm and their ability to penetrate and fertilize an egg.   

Learn more about female health by visiting our hub.

What is progestin?

Progestin, also called progestogen, is a synthetic form of progesterone. Progestins mimic the way that progesterone works in the body. Progestins are used in medications primarily for birth control, either alone or in combination with estrogen.

Intrauterine devices, implants, injections, and the progesterone-only pill all use progestin to stop or significantly reduce ovulation. Combined oral contraceptives, the patch, and the hormonal vaginal contraceptive ring prevent pregnancy by using a combination of progestin and estrogen. The typical-use failure rate ranges from 0.1% to 7%, depending on the method used.

Some research suggests that progestin-only contraceptives are often appropriate for many females with contraindications to estrogen-containing contraceptives and females who prefer to avoid estrogen exposure.

Progestin can also be useful for:

  • the absence of menstruation
  • irregular menstruation
  • severe and frequent menstrual cramps
  • unusual uterine bleeding
  • endometriosis-related pain
  • emergency contraception
  • postmenopausal hormone replacement therapy (HRT)

What happens if my progesterone levels are atypical?

Atypical progesterone levels could indicate a problem with ovulation, menstruation, or both. They may contribute to infertility.

High levels

A female’s levels of progesterone fluctuate monthly. One older paper suggests that high levels of progesterone may help protect against ovarian cancer.

Sometimes, a high level of progesterone can indicate:

Low levels

Low progesterone levels can affect both menstruation and fertility. Progesterone levels typically decline as a female ages. These lower levels can signal the start of perimenopause and menopause.

Progesterone is present at much lower levels in males than in females. Low levels may indicate an adrenal gland disorder.

What are the medical uses of progesterone?

Progesterone is often used to regulate menstruation in females who are not menstruating and to bring on menstruation in females who have not yet reached menopause but are not menstruating due to low levels of progesterone.

It is sometimes used to treat unusual uterine bleeding caused by a hormonal imbalance.  

A study from 2013 suggests that progesterone can safely reduce the risk of preterm birth in females at high risk who have delivered early in previous pregnancies and who have an ultrasound-confirmed short cervix.

Birth control

Females who cannot use birth control methods that combine estrogen and progesterone can use pills that contain only progesterone. This option has a typical-use failure rate of 7%.

Hormone replacement therapy

Progesterone is one of the hormones used in HRT in postmenopausal females. It is used to prevent overgrowth in the lining of the uterus, which could lead to cancer.

Visit our hub to read more about birth control.

What are the side effects of progesterone treatments?

Side effects of progesterone treatments include:

Summary

Progesterone is a hormone that plays a role in female and male reproductive systems.

Low levels of progesterone can lead to menstrual irregularities and fertility challenges. These issues are often treatable by supplementing your levels of progesterone with progestin.  

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Medical Reviewer: Sanaz Ghazal, MD, FACOG
Last Review Date: 2022 May 12
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