Progesterone: Why This Hormone Matters

Progesterone is an important hormone that plays many roles in a woman’s health. It works closely with estrogen and helps keep the body in balance.

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Where Progesterone Comes From

Progesterone is mainly made in the ovaries after ovulation. Each month, when an egg is released, a structure called the corpus luteum forms and begins producing progesterone.

Progesterone is the main hormone during the second half of the menstrual cycle (called the luteal phase). Its job is to prepare the lining of the uterus for pregnancy.

• If pregnancy occurs, progesterone helps support it.

• If pregnancy does not occur, progesterone levels fall and a new menstrual cycle begins.

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Progesterone and Mood

Progesterone has a strong effect on the brain and nervous system. One of its byproducts, called allopregnanolone, works on calming receptors in the brain. These are the same receptors affected by medications used for anxiety and sleep.

Because of this, progesterone can:

• Promote calmness

• Reduce anxiety

• Improve mood

• Support better sleep

Progesterone also helps serotonin work more effectively. Serotonin is a key chemical involved in happiness and emotional balance.

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Progesterone and the Immune System

During pregnancy, progesterone helps the immune system tolerate the developing baby. It also has natural anti-inflammatory effects.

This may explain why some autoimmune conditions improve during pregnancy, when progesterone levels are high.

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Progesterone and Fluid Balance

Progesterone helps prevent excess water retention by opposing aldosterone, a hormone that causes the body to hold onto sodium and water. This can reduce:

• Bloating

• Swelling

• Edema

These symptoms often occur when estrogen is too high relative to progesterone.

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Progesterone and Brain Protection

Progesterone is considered a neurosteroid, meaning it supports brain health. It helps with:

• Normal nerve development

• Protection of brain tissue after injury

Research suggests progesterone may help protect against traumatic brain injury, which may partly explain why females appear less vulnerable to certain brain injuries.

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Progesterone and Breast Health

Progesterone plays a major role in breast development, beginning at puberty. During the second half of the menstrual cycle, rising progesterone levels can cause:

• Breast fullness

• Tenderness

• Swelling

These symptoms are common and normal during the luteal phase.

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Other Important Roles of Progesterone

Progesterone also:

• Calms uterine contractions

• Raises body temperature after ovulation

• Supports bone growth

• Helps regulate blood clotting

• Supports thyroid function

• Aids in fat metabolism

• Supports healthy levels of zinc and copper

• May help protect against certain female cancers

Progesterone is often described as a natural antidepressant because of its calming and mood-stabilizing effects.

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Progesterone and Aging

Progesterone is typically the first hormone to decline with age, often dropping during perimenopause. This decline can contribute to symptoms such as:

• Anxiety

• Sleep problems

• Mood changes

• Irregular cycles

• Breast tenderness

• Weight gain

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Bottom line for patients:

Progesterone is not just a “reproductive hormone.” It plays a vital role in mood, sleep, brain health, immune balance, and overall well-being—especially as women move into midlife.