Estradiol and Progesterone Together: Why Many Women Need Both

Why estrogen alone isn't enough if you have a uterus

Estradiol is what relieves most menopause symptoms: hot flashes, night sweats, vaginal dryness and the sleep disruption that comes with them. But estrogen also tells the lining of the uterus (the endometrium) to grow. Before menopause, progesterone from ovulation balances that each month and the lining sheds as a period. After menopause, if you take estrogen without anything to balance it, the lining can keep thickening.

Over time that thickening can become endometrial hyperplasia, and some forms of hyperplasia can progress to endometrial cancer. This is the single most important reason hormone therapy for women with a uterus combines two hormones.

By the numbers

What happened to the uterine lining over 3 years (PEPI trial)

22.7%of women on estrogen alone developed complex hyperplasia, vs 0.8% on placeboSource: PEPI 1996

11.8%on estrogen alone developed atypical hyperplasia, vs 0% on placeboSource: PEPI 1996

596women aged 45 to 64 were randomized; every estrogen-plus-progestogen group had hyperplasia rates similar to placeboSource: PEPI 1996

A Cochrane review of 46 trials reached the same conclusion: unopposed estrogen raises hyperplasia risk at every dose studied, and adequate progestogen brings it back to placebo levels (Furness 2012). The Menopause Society recommends a progestogen for every woman with a uterus who takes systemic estrogen (The Menopause Society 2022).

That applies to every systemic route: pills, patches, gels, skin creams and dissolving tablets. See oral vs patch vs cream estradiol for how the routes differ.

What if you've had a hysterectomy?

Without a uterus, there is no lining to protect, so most women who've had a hysterectomy take estrogen alone. There are exceptions, such as a history of endometriosis, where a clinician may still add a progestogen. Our guide to estrogen after hysterectomy covers this in detail.

Progesterone vs progestins: not all progestogens are the same

"Progestogen" is the umbrella term for anything that acts like progesterone. There are two main kinds:

• Micronized progesterone is chemically identical to the progesterone your ovaries make. It is finely ground so it absorbs well by mouth. The FDA-approved version is sold as Prometrium, and it is also widely available as a generic and through compounding.
• Synthetic progestins, such as medroxyprogesterone acetate or norethindrone acetate, are molecules designed to act on progesterone receptors. They are effective at protecting the lining, but they also act on other receptors and behave differently in the body.

Both protect the uterus. The differences that interest women and clinicians most are about breast cancer, blood clots and sleep.

Breast cancer

The type of progestogen appears to matter. In the French E3N cohort of more than 80,000 postmenopausal women, estrogen combined with progesterone was not associated with higher breast cancer risk (relative risk 1.00), while estrogen combined with other synthetic progestins was (1.69). Estrogen alone was associated with a smaller increase (1.29) (Fournier 2008).

That was an observational study, so it can't prove cause and effect. A 2018 expert review concluded that estrogen plus oral micronized progesterone does not appear to raise breast cancer risk for up to about 5 years of use, that there is limited evidence of a higher risk beyond 5 years, and that every woman on combined therapy should be counseled about breast cancer risk regardless of the progestogen (Stute 2018).

Blood clots

In the ESTHER case-control study, micronized progesterone was not associated with higher blood clot risk (odds ratio 0.7), while one group of synthetic progestins (norpregnane derivatives) was associated with roughly four times the risk (3.9) (Canonico 2007). Again, this is observational evidence, but it is one reason micronized progesterone is often preferred.

Sleep

Progesterone has a calming effect on the brain. The prescribing information for FDA-approved micronized progesterone notes that it can cause drowsiness and dizziness and says to take it as a single daily dose at bedtime (Prometrium label). In a small randomized crossover study of 10 postmenopausal women, 300 mg of oral micronized progesterone at night reduced time spent awake during the night without affecting next-day thinking (Schüssler 2008). More on this in progesterone and sleep.

Common ways the two are combined

There are two broad patterns. Your clinician chooses based on how long it's been since your last period, your bleeding pattern and your preferences (The Menopause Society 2022).

As an example of a cyclic schedule, the FDA-approved micronized progesterone label describes 200 mg at bedtime for 12 days of each 28-day cycle alongside daily estrogen (Prometrium label). Continuous schedules use a daily dose instead. The exact dose depends on your estrogen dose and route, which is why it should be set by your clinician.

What about progesterone creams?

Progesterone creams rubbed on the skin produce low and variable blood levels. Researchers still debate how much they affect the uterine lining, and they haven't been shown to protect it reliably the way oral progesterone does (Stanczyk 2005). That is why guidelines rely on oral micronized progesterone or other proven progestogens for endometrial protection (The Menopause Society 2022).

Side effects to know about

Most women tolerate micronized progesterone well, but side effects can happen, especially in the first few months. Those listed in the Prometrium prescribing information include (Prometrium label):

• Drowsiness and dizziness (the reason for bedtime dosing)
• Breast tenderness
• Headache
• Bloating
• Mood changes
• Nausea

The brand-name capsules contain peanut oil, so tell your clinician about a peanut allergy. Compounded capsules may use different ingredients, and your pharmacy can tell you what's in yours.

Treatment options

If you have a uterus and your clinician recommends systemic hormone therapy, you'll be offered an estrogen and a progestogen. The common combinations include:

• An estradiol patch or gel with oral micronized progesterone
• An estradiol tablet with oral micronized progesterone
• A combined estrogen-progestin patch or pill
• Estrogen with a progestin-releasing IUD, used off-label for endometrial protection in some women

Amie HRT+ is a compounded prescription of estradiol and progesterone, prescribed together. A licensed clinician reviews your symptoms, health history and medications, decides whether it's appropriate for you, and chooses the strength of each. Compounded medications are not FDA-approved, and your clinician can discuss FDA-approved options too.

Questions to ask your clinician

• Do I need a progestogen, and which one are you recommending?
• Cyclic or continuous: what bleeding should I expect?
• When should I take it, and what if I miss a dose?
• What bleeding or side effects should prompt a call?
• How often will we review my treatment?

For a broader overview, see our guide to hormone replacement therapy.