The primary hormone you lose during menopause is estrogen, specifically a form called estradiol. Estradiol levels drop from a typical range of 100 to 250 picograms per milliliter during reproductive years to roughly 10 picograms per milliliter after menopause. Progesterone, the other major ovarian hormone, also declines significantly. Together, the loss of these two hormones drives virtually every symptom and long-term health change associated with menopause.
Why Estrogen and Progesterone Drop
Your ovaries contain a finite number of follicles, the tiny structures that release an egg each month. Every menstrual cycle, follicles produce estradiol during the first half and both estradiol and progesterone during the second half. As you age, the number of remaining follicles steadily shrinks. When the supply runs low enough, your brain tries to compensate by producing more follicle-stimulating hormone (FSH), essentially sending a louder signal to the ovaries to keep working. Eventually the ovaries can no longer respond, estradiol production drops sharply, ovulation stops, and progesterone production ceases along with it.
FSH levels reflect this process in reverse. They begin climbing about six years before your final menstrual period and eventually reach a plateau around 64 mIU/mL, nearly 14 times higher than typical male levels. An FSH reading above 25 mIU/mL, combined with at least 60 days without a period, is one of the clinical markers used to identify late perimenopause.
Perimenopause: The Unpredictable Phase
The transition to menopause doesn’t happen in a smooth downward curve. During perimenopause, which can begin as early as your early 40s, estrogen levels swing erratically. On some days estrogen may spike higher than normal, and on others it may drop precipitously. These wild fluctuations are often more disruptive than the eventual low levels of postmenopause, causing irregular periods, hot flashes, sleep disruption, and mood changes that can feel unpredictable from week to week.
Progesterone tends to decline more steadily during this phase. Because ovulation becomes inconsistent, the second half of the cycle (which depends on the structure left behind after an egg is released) produces less and less progesterone. This imbalance between still-fluctuating estrogen and falling progesterone contributes to heavier or irregular bleeding that many women experience in their mid-to-late 40s.
Other Hormones That Change
Testosterone also declines in midlife, but this appears to be driven by aging rather than menopause itself. Median testosterone concentrations drop from about 0.56 nmol/L in women aged 40 to 44 down to 0.42 nmol/L by the late 50s, then modestly rebound. Notably, when researchers compared women of the same age at different menopausal stages, testosterone levels did not differ, suggesting the decline is a function of getting older rather than losing ovarian function specifically.
Two lesser-known hormones also disappear during the transition. Anti-Müllerian hormone (AMH) reflects how many follicles remain in the ovaries. It declines steadily and reaches near-undetectable levels about five years before your final period. Inhibin B, produced by the same follicle cells, follows a similar pattern and drops below detectable levels around the same time. The loss of inhibin B is part of what allows FSH to rise, since inhibin normally keeps FSH in check.
What Estrogen Loss Does to Your Body
Estrogen receptors are spread throughout the body, not just in reproductive organs. The brain has significant concentrations of them in areas involved in memory, mood regulation, and body temperature control. Research using brain imaging has found that higher receptor density in memory-related brain regions after menopause is associated with lower memory scores and more self-reported cognitive and mood symptoms. This helps explain why many women notice changes in focus, word recall, and emotional regulation during and after the transition.
Bone is one of the most affected tissues. Estrogen helps regulate the cycle of bone breakdown and rebuilding. When estrogen drops, breakdown outpaces rebuilding, and up to 20% of bone density can be lost during menopause and the years immediately surrounding it, according to the Endocrine Society. This rapid loss is why osteoporosis risk rises sharply in the postmenopausal years.
The cardiovascular system is also affected. Estrogen supports blood vessel flexibility and helps maintain favorable cholesterol profiles. After menopause, LDL (“bad”) cholesterol tends to rise while the protective effects on blood vessel walls diminish. The skin, urinary tract, and vaginal tissue all contain estrogen receptors too, which is why dryness, thinning tissue, and urinary changes are so common.
Hormone Therapy Basics
Hormone therapy replaces some of the estrogen your ovaries no longer make. It comes in several forms: oral tablets, skin patches, gels, and vaginal preparations. Patches and gels deliver estradiol through the skin and are generally preferred because they bypass the liver. Vaginal estrogen treats localized symptoms like dryness and urinary discomfort without raising whole-body hormone levels significantly.
If you still have a uterus, any estrogen therapy is paired with a progestogen to protect the uterine lining from overgrowth. Women who have had a hysterectomy typically take estrogen alone. Low-dose options are available for women who want symptom relief with minimal hormone exposure, while some women with severe hot flashes may need higher doses. The choice depends on your symptoms, health history, and how recently menopause began.
The Timeline at a Glance
- Early 40s: AMH and inhibin B are declining. Progesterone begins to drop as ovulation becomes less reliable. Estrogen may still be normal or start fluctuating.
- Mid-to-late 40s: Perimenopause is underway for most women. Estrogen swings unpredictably, FSH climbs, and cycle length becomes irregular.
- Around age 51 (average): The final menstrual period occurs. Estradiol settles to roughly 10 pg/mL. Progesterone production from the ovaries essentially stops.
- First five postmenopausal years: The most rapid bone loss occurs. Cardiovascular risk markers shift. Symptoms like hot flashes often peak and then gradually improve for many women, though they can persist for a decade or more.