What Is Progesterone?

A Sex Hormone Involved In Menstruation, Pregnancy, and More

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Progesterone is a sex hormone that plays a key role in the menstrual cycle and supporting a pregnancy. It's also responsible for breast development and preparing the body for breastfeeding.

Progesterone keeps a balance with estrogen, the other primary sex hormone in those assigned female at birth.

This article will explore progesterone's functions, cycles, and its supplemental forms.

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Where It's Made

Progesterone is primarily produced by a part of the ovary called the corpus luteum. The corpus luteum develops from the follicle that releases an egg from the ovary for ovulation.

Progesterone is also made by the placenta, an organ that develops during pregnancy to help support the fetus, and to a lesser degree by the adrenal glands, which release hormones for a variety of bodily functions.

Although it's commonly referred to as a female sex hormone, progesterone is also made in the adrenal glands and testes of those assigned male a birth. Progesterone helps to produce testosterone, the primary sex hormone in males.

Recap

Progesterone is produced primarily by the ovary (after ovulation) and the placenta (during pregnancy). It's also made in lesser amounts by the adrenal glands and the testes.

Function

Progesterone plays a few different roles, starting with causing breasts to grow at puberty.

It is the dominant hormone in the second half of a menstrual cycle called the luteal phase. The luteal phase begins after ovulation and goes until the first day of your period.

Its main jobs? Preparing the body for pregnancy and supporting one, should it occur.

Breast Development

Beginning at puberty, progesterone stimulates the growth of breast tissue.

During each luteal phase, this tissue is stimulated, but it's not until you become pregnant that progesterone completes the job of preparing your breasts for milk production and lactation that allows for breastfeeding. 

The increase in progesterone in the luteal phase of your menstrual cycle is thought to be the cause of the breast swelling, pain, and tenderness that often occurs in this phase of your cycle.

Breast pain (mastalgia) is a common symptom of premenstrual syndrome (PMS).

Menstrual Cycle

After ovulation, the corpus luteum ramps up its progesterone production. This is to continue the work of estrogen in preparing the lining of your uterus so that it can accept a fertilized egg and the egg can be implanted for pregnancy.

If you do not become pregnant, then your corpus luteum dissolves and your progesterone levels drop, causing the uterine lining to start to break down.

This results in a period and a new menstrual cycle begins.

Pregnancy

If the egg that's released is fertilized by a sperm and you become pregnant, the corpus luteum continues to produce progesterone until about 10 weeks of pregnancy.

Progesterone is so important to achieve and maintain a healthy pregnancy that at around 10 weeks, your placenta takes over the production of progesterone for the remainder of your pregnancy.

Research suggests that progesterone may have anti-inflammatory activity and influence over your immune system. These functions of progesterone may help protect an early developing pregnancy from miscarriage and prevent against later pregnancy loss and preterm labor (i.e., that which occurs before the 37th week of pregnancy).

Recap

Progesterone levels fluctuate throughout the menstrual cycle and are increased after ovulation to prepare the uterus for pregnancy. If a pregnancy occurs, progesterone is produced by the placenta to help maintain the pregnancy. Progesterone is also responsible for breast growth at puberty and to preparations for breastfeeding.

Associated Conditions

If progesterone levels are too low, it can lead to issues such as:

Your healthcare provider can check your progesterone levels through a blood test and may prescribe a supplemental form if levels too low.

Mood and Energy Levels

Like estrogen, progesterone interacts with the chemicals in your brain to control your mood and your general sense of well-being.

One way progesterone does this is via its metabolite, a compound known as allopregnanolone.

Allopregnanolone works on a particular receptor in your brain called the GABA receptor. It typically has anxiety-busting action and a calming quality similar to the actions of alcohol and other sedative drugs like the benzodiazepines.

This can obviously be beneficial. However, it is also why you may feel sleepy or a little low energy right before your period. It also contributes to fatigue that's common during the early part of pregnancy.

But for some people, the luteal phase rise in progesterone can cause varying degrees of anxiety and agitation.

It is thought that this opposite reaction is caused by a disruption in how you process allopregnanolone.

Progesterone Supplements

Supplemental progesterone that's made from natural or synthetic sources can be prescribed for a variety of reasons ranging from pregnancy support to contraception.

Methods for supplementing progesterone include:

  • Tablets taken by mouth
  • Shots into a muscle, known as intramuscular injections
  • Vaginal gels or suppositories (a solid medication inserted into the vagina)

Because progesterone is so rapidly cleared from the body when given by mouth, it makes it difficult to use progesterone this way, especially if it is needed only in smaller doses.

Micronized progesterone, which means it is decreased in particle size for longer effect, can be taken in some instances. It may be prescribed as part of a menopausal hormone replacement regime or to restore periods if you are not menopausal but stop getting periods.

Progestins, medications that have similar properties to progesterone, provide an option that can be effective when taken by mouth.

For Pregnancy After IVF

For some women, it may be necessary to take supplemental progesterone during pregnancy.

If you conceived with the help of in vitro fertilization (IVF), a form of assisted reproductive technology, you likely did not ovulate naturally so your corpus luteum may not not produce enough progesterone.

Your healthcare provider may recommend some type of progesterone support either in the form of a vaginal gel or suppository, tablet, or injections until about 10 to 12 weeks of pregnancy.

Supplemental progesterone may also be used during IVF or intrauterine insemination (IUI) to encourage a pregnancy.

For Preterm Labor Prevention

If you have a history of preterm delivery and/or preterm premature rupture of membranes in a previous pregnancy, you may be a candidate to use progesterone injections to try to prevent another preterm birth.

These are weekly injections of a specific type of progesterone that usually begin at 16 to 24 weeks and continue through 36 weeks of pregnancy.

For Contraception

Oral medications with progestins are commonly used as a contraceptive to prevent pregnancy since an increase in progesterone and its properties prevents ovulation.

By manipulating the chemical structure of natural progesterone, different synthetic progestins have been created that act on the progesterone hormone receptors in your body.

Progestins are used in all hormone-containing contraceptives including:

Most of these synthetic progestins are derived from testosterone. Depending on the type of progestin it may have more or less testosterone-like activity. 

For Conditions That Cause Excess Estrogen

Progesterone and estrogen act together not only to prepare the body for pregnancy, but to support many other bodily functions. Progesterone's action on the lining of the uterus is where it really functions as estrogen's sidekick.

In a normal menstrual cycle in which you don't become pregnant, the buildup and shedding of the lining of your uterus are controlled by a balance between estrogen and progesterone.

If you have a condition where you are not ovulating but have excess estrogen—which is the case in polycystic ovary syndrome (PCOS) and occasionally in obesity—your healthcare provider may suggest the use of a progestin to help protect the lining of your uterus and to treat any abnormal uterine bleeding that may result.

For Hormone Replacement Therapy

Progestins are also typically used in many hormone replacement options for the management of menopause symptoms. When you are in menopause, the majority of the unpleasant symptoms, such as hot flashes, are caused by a lack of estrogen.

Taking an estrogen replacement alone will effectively treat these symptoms and protect your bones. However, if you still have your uterus, you may need to also use a progestin or progesterone supplement to prevent abnormal growth of your endometrium or reduce the risk of endometrial cancer.

Recap

Progesterone can be supplemented if levels are too low or to help manage conditions where its counterpart estrogen is too high. It can also be used to either prevent or help sustain a pregnancy and is sometimes used in hormone replacement therapy during menopause. Forms include pills, shots, vaginal gels, and suppositories.

Summary

Progesterone is a sex hormone that plays crucial roles in the menstrual cycle and all stages of pregnancy. It also plays a role in breast development and preparing for breastfeeding.

In males, progesterone produced by the adrenal glands and testes plays a role in making testosterone.

Progesterone can be supplemented if levels are too low or to support a pregnancy if there are certain risks, such as a history of preterm birth.

Progestins, which act similar to progesterone, are commonly used in hormonal contraceptives and hormone replacement therapy during menopause.

A Word From Verywell

It is important to understand the many roles progesterone plays in the body and how it may affect your moods and energy levels in many different ways.

If you have any concerns about your hormone levels, discuss it with your healthcare provider. You can have your progesterone levels checked and explore your options.

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