• Menopause

Understanding Estrogen and Progesterone: Roles, Differences, and HRT Explained

Medically reviewed and edited by Lauren Cramer, PA- C

Published: August 13, 2025
Updated: November 11, 2025
3 mins

Hormones play an important role in every stage of a woman’s life, from puberty and menstruation to pregnancy and menopause. Among the most essential female sex hormones are estrogen and progesterone – two chemical messengers that influence everything from reproductive health to mood, metabolism, and bone density.

In this article, we’ll break down what estrogen and progesterone are, how they differ, how they complement one another, and why they’re commonly prescribed together in hormone replacement therapy (HRT) to relieve menopausal symptoms and support long-term health.

What is Estrogen?

Estrogen is one of the primary female sex hormones, responsible for a wide range of functions in the body. Estrogen is mainly produced by the ovaries, but smaller amounts are also made by the adrenal glands and fat tissue, especially after menopause. Throughout a woman’s life, estrogen levels naturally rise and fall in response to different hormonal stages – puberty, menstrual cycles, pregnancy, perimenopause, and menopause.

Estrogen is actually a group of hormones that work together to regulate female reproductive and systemic health:

• Estradiol (E2): The most common form during the reproductive years

• Estriol (E3): The primary estrogen during pregnancy

• Estrone (E1): The only type produced after menopause

Estrogen has a wide range of functions, including:

• Regulating the menstrual cycle by helping to grow the uterine lining in preparation for a potential pregnancy

• Supporting bone health by preserving bone density

• Influencing mood and brain function, including memory and emotional regulation

• Promoting breast development and uterine growth during puberty and pregnancy

Because estrogen levels fluctuate naturally throughout life, women may notice shifts in mood, energy, libido, and physical health as hormone levels rise or drop. 

During reproductive years, estrogen is produced primarily by the ovaries, and to a lesser extent by the adrenal glands and fat tissue.

What Does Estrogen Do?

• Maintains the uterine lining for potential pregnancy

• Supports bone strength by reducing bone breakdown

• Regulates brain neurotransmitters such as serotonin and dopamine, influencing mood and cognition

• Promotes vascular health, keeping arteries flexible

• Enhances collagen production, skin elasticity, and hair quality

• Aids vaginal and urinary tissue health

• Modulates metabolism, insulin sensitivity, and body composition

As estrogen declines during perimenopause and menopause, these systems begin to lose their resilience – manifesting as hot flashes, mood swings, poor sleep, joint pain, brain fog, and bone loss.

Transdermal estradiol (patch, gel, or cream) is the most physiologic and heart-protective form of estrogen therapy.

What is Progesterone?

Progesterone is a crucial hormone in the female reproductive system that helps regulate the menstrual cycle and prepare the body for pregnancy. This hormone works closely with estrogen to keep your reproductive system functioning smoothly.

Progesterone is primarily produced by the ovaries after ovulation, during the second half of the menstrual cycle. If pregnancy occurs, the placenta takes over progesterone production to help support the developing fetus.

One of progesterone’s main roles is to prepare the uterus for pregnancy. After ovulation, progesterone helps thicken and maintain the uterine lining, creating a nourishing environment where a fertilized egg can implant and grow.

Beyond fertility, progesterone serves several other key functions:

• Regulates the menstrual cycle and maintains a regular cycle by balancing the effects of estrogen

• Supports early pregnancy by preventing the uterus from contracting prematurely

• Contributes to mood stability and may help reduce symptoms of anxiety or irritability

• Promotes restful sleep, particularly in the second half of the menstrual cycle

Because progesterone plays such a balancing role, fluctuations in its levels can have noticeable effects on your body and mind.

Progesterone is produced after ovulation by the corpus luteum in the ovaries and later by the adrenal glands. During the reproductive years, it balances estrogen’s growth-stimulating effects on tissues such as the endometrium (uterine lining) and breast.

What Does Progesterone Do?

• Protects the uterine lining from overgrowth (endometrial hyperplasia) caused by estrogen

• Supports calm, stable mood and better sleep by increasing GABA activity in the brain

• Promotes bone formation and works synergistically with estrogen in maintaining bone density

• Helps regulate fluid balance and immune modulation

• Contributes to breast and cardiovascular health

How Estrogen and Progesterone Work Together

Think of estrogen as the builder and progesterone as the architect who ensures what’s built remains structurally sound.

Estrogen stimulates tissue growth – such as thickening the uterine lining or supporting collagen and bone turnover. Progesterone follows, stabilizing that growth and signaling balance.

When both are present in proper proportions:

• The uterus stays healthy (no overgrowth)

• Sleep and mood stabilize

• Cognitive clarity and metabolic regulation improve

• Breast tenderness and fluid retention are minimized

During perimenopause, ovulation often becomes irregular – so progesterone production drops first, while estrogen fluctuates wildly. The result? Estrogen dominance: symptoms like anxiety, breast tenderness, heavy periods, bloating, and sleep disruption.

Hormonal imbalance can present differently depending on life stage or underlying condition. In PCOS, the ovaries produce excessive androgens, while ovulation (and therefore progesterone production) is infrequent – leading to estrogen dominance, irregular cycles, acne, and mood changes. 

During perimenopause, estrogen levels fluctuate unpredictably while ovulation becomes sporadic, resulting in erratic progesterone output; women often feel anxious, sleep-deprived, and experience heavy or irregular bleeding. In menopause, both hormones decline, but progesterone falls to near zero while low, steady estrogen contributes to dryness, fatigue, cognitive fog, and bone loss. 

Each scenario represents a different type of imbalance – too much estrogen relative to progesterone, or too little of both – and requires an individualized, balanced replacement strategy to restore harmony and function.

Throughout the menstrual cycle, estrogen and progesterone follow a carefully timed rhythm:

• In the first half of the cycle, estrogen rises to stimulate the growth of the uterine lining (endometrium), preparing the body for a possible pregnancy.

• After ovulation, progesterone levels increase to stabilize and support that lining, making it suitable for a fertilized egg to implant.

• If pregnancy doesn’t occur, both hormone levels drop, triggering menstruation and the start of a new cycle.

Beyond reproduction, estrogen and progesterone also have complementary effects on other systems in the body. Estrogen influences mood, cognition, and bone density, while progesterone helps counterbalance those effects by calming the nervous system, supporting sleep, and maintaining hormonal stability.

Maintaining a healthy balance between estrogen and progesterone is critical. Too much or too little of either hormone can lead to a range of issues, including:

• Polycystic ovary syndrome (PCOS): Often associated with higher estrogen and low progesterone, leading to irregular or absent periods

• Menstrual irregularities: Imbalances can cause heavy bleeding, short cycles, or missed periods

• Perimenopause and menopause: As hormone production declines, women may experience hot flashes, mood swings, sleep disruptions, and other symptoms tied to hormonal shifts

When estrogen and progesterone are in sync, they promote a state of balance that supports both reproductive and whole-body health. Disruptions in that balance can be frustrating — but with the right care, they can often be addressed through lifestyle changes, medications, or hormone therapy.

Key Differences Between Estrogen and Progesterone

While estrogen and progesterone work together, they have distinct roles and characteristics. Understanding these differences can help clarify how each hormone affects your body — and why balance between them is so important.

Here’s a breakdown of the key differences:

While estrogen tends to be the more dominant hormone in the first half of the cycle, progesterone plays a leading role in the second half. Their alternating rise and fall help regulate not just fertility but also brain function, sleep patterns, bone health and physical well-being.

When one hormone outweighs the other for an extended period – such as in estrogen dominance or low progesterone states – you might experience symptoms like mood swings, irregular periods, or trouble sleeping. That’s why maintaining a healthy estrogen-progesterone ratio is essential for hormonal balance.

What Happens If You Take Progesterone Without Estrogen?

In a postmenopausal woman, taking progesterone alone may help with sleep, anxiety, and mild mood symptoms – but it won’t relieve estrogen-deficiency symptoms such as hot flashes, vaginal dryness, bone loss, or cognitive changes.

Without adequate estrogen, progesterone’s calming benefits may plateau, and bone or cardiovascular protection may be incomplete.

What Happens If You Take Estrogen Without Progesterone?

Taking estrogen without progesterone is sometimes appropriate, but it depends on whether a woman has a uterus. Estrogen-only therapy can effectively relieve menopausal symptoms such as hot flashes, vaginal dryness, and mood changes.

However, for women with an intact uterus, using estrogen alone over time can lead to the overgrowth of the uterine lining (endometrial hyperplasia), which increases the risk of uterine cancer. That’s why progesterone is typically added to HRT for women with a uterus, since it balances estrogen’s effects on the uterine lining and reduces health risks.

Women without a uterus, on the other hand, can safely use estrogen-only therapy since there’s no uterine tissue at risk. Still, it’s important to use the lowest effective dose for the shortest duration necessary and follow up regularly with a healthcare provider. If a woman still has her uterus and takes estrogen without progesterone, the unopposed estrogen stimulates continuous growth of the uterine lining.

Over time, this can lead to:

• Endometrial hyperplasia (thickened lining)

• Irregular or breakthrough bleeding

• Increased risk of endometrial cancer

Even low-dose vaginal estrogens typically don’t require progesterone due to minimal systemic absorption – but any systemic estrogen (patch, cream, gel, oral, injection) must be balanced with progesterone to keep the uterus safe.

For women without a uterus (post-hysterectomy): estrogen alone may be okay, however, our recommendation is to always take these two together, as progesterone has a wide positive effect on the body, not only to protect a uterus.

Where Can I Learn More About Hormone Balance?

If you're experiencing symptoms associated with hormonal imbalance, you don’t have to tough it out alone. With personalized hormone therapy, expert guidance, and support that fits your life, getting back to balance is more accessible than ever – thanks to the LifeMD Women’s Health Program.

Make an online appointment and take the first step toward feeling like you again.

Lauren Cramer, PA- C

Lauren is a passionate and dedicated board-certified physician assistant. She received her Bachelor’s degree in Kinesiology and Exercise Science from SUNY Cortland — graduating magna cum laude while competing as a three-sport collegiate athlete in indoor and outdoor track and cross country. She went on to complete her Master’s degree in Biological Sciences and earn her Physician Assistant degree from Daemen College in Buffalo, New York. Lauren has years of focused experience in perimenopause, menopause, and postmenopause care, specializing in hormone replacement therapy (HRT), bone health optimization, and a functional medicine approach to women’s wellness. She integrates evidence-based hormone therapy with lifestyle, nutrition, and metabolic strategies to support long-term vitality, cognitive health, and bone density. In addition to her women’s health expertise, Lauren has a well-rounded background in allergy, asthma, otology, laryngology, and rhinology. Functional medicine has always been a passion of hers, and she continues to pursue advanced certification to deepen her ability to deliver personalized, root-cause care to her patients.

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