Micronized progesterone in hormone therapy

Micronized progesterone is progesterone itself, the hormone your ovaries make after ovulation, processed into fine particles so it can be absorbed from a capsule. In menopausal hormone therapy its job is to protect the uterine lining from the overgrowth that estrogen alone would cause. It is FDA-approved for that purpose in women taking estrogen, it is taken at bedtime because it can cause drowsiness, and in observational studies it has looked more favorable than synthetic progestins for breast cancer and blood clots, although randomized proof is lacking.

What it is, and what it is not

Progestogen is the family name for any compound that acts like progesterone. The family has two branches.

	Micronized progesterone	Synthetic progestins
Molecule	Identical to ovarian progesterone	Modified structures (medroxyprogesterone acetate, norethindrone, levonorgestrel, others)
Forms in hormone therapy	100 mg and 200 mg oral capsules	Pills, combination patches and pills, hormonal IUD
Used in the WHI?	No	Yes (medroxyprogesterone acetate)
FDA-approved for endometrial protection?	Yes	Yes

Micronized progesterone capsules are suspended in peanut oil. The FDA label states they should never be used by anyone allergic to peanuts.

It is also distinct from compounded “bioidentical” progesterone creams. An FDA-approved capsule has a verified dose; a compounded cream does not, and a systematic review concluded that transdermal micronized progesterone does not provide endometrial protection. US guidelines recommend FDA-approved products over compounded ones.

Why a progestogen is needed with estrogen

Estrogen stimulates the endometrium. Taken alone by a woman with a uterus, it leads to hyperplasia, an overgrowth that can progress to cancer. A progestogen reverses that.

The size of the effect is stark. In the trial that supports the FDA label, 358 postmenopausal women with a uterus were treated for up to 3 years:

Group	Endometrial hyperplasia	Atypical hyperplasia (precancerous)
Conjugated estrogen alone	64%	12%
Conjugated estrogen plus progesterone 200 mg, 12 days per cycle	6%	1%
Placebo	3%	0%

The 6 percent with progesterone was mostly simple hyperplasia, which is not precancerous. Women who have had a hysterectomy do not need a progestogen at all.

FDA-approved use and dosing

The approved indication is prevention of endometrial hyperplasia in postmenopausal women with a uterus who are taking conjugated estrogens. The approved regimen is 200 mg once daily at bedtime for 12 days of each 28-day cycle. The capsules are also approved for secondary amenorrhea.

In practice two schedules are common.

Schedule	Dose	Bleeding pattern	Evidence
Cyclic (sequential)	200 mg for 12 to 14 days each month	Predictable monthly withdrawal bleed	FDA-approved; systematic review supports endometrial protection for up to 5 years
Continuous	100 mg every night	Usually no bleeding after the first months	Widely used in US practice; off-label; less formal trial support

A 2016 systematic review concluded that oral micronized progesterone protects the endometrium when given sequentially for 12 to 14 days a month at 200 mg for up to 5 years, that vaginal progesterone may protect when used at least 10 days a month (off-label), and that transdermal progesterone does not. Continuous 100 mg nightly has thinner formal evidence, which is one reason the label advises that persistent or recurring abnormal bleeding on any regimen be evaluated, including with endometrial sampling when indicated.

Side effects

In the 3-year placebo-controlled trial of 875 postmenopausal women, these reactions were more common with estrogen plus cyclic progesterone than with placebo:

Reaction	Estrogen plus progesterone	Placebo
Headache	31%	27%
Breast tenderness	27%	6%
Depression	19%	12%
Dizziness	15%	9%
Abdominal bloating	12%	5%

Hot flashes were reported by 11 percent on treatment versus 35 percent on placebo, a reminder of what the estrogen was doing. Breast tenderness and bloating are often attributed to the progestogen component and may ease with a lower dose or a continuous schedule.

The label warns that progesterone may cause transient dizziness and drowsiness, directs a single dose at bedtime, and advises caution about driving or operating machinery until you know your response. For many women the sedation is welcome.

Breast cancer: how it compares with synthetic progestins

The WHI’s breast cancer signal came from conjugated estrogen plus medroxyprogesterone acetate. Whether micronized progesterone carries the same risk is unknown from randomized trials. The best observational evidence is the French E3N cohort of 80,377 postmenopausal women followed for about 8 years:

Regimen	Relative risk of breast cancer
Estrogen plus micronized progesterone	1.00 (0.83 to 1.22)
Estrogen plus dydrogesterone	1.16
Estrogen plus other synthetic progestins	1.69 (1.50 to 1.91)
Estrogen alone	1.29

The authors concluded that the choice of progestogen matters and that progesterone or dydrogesterone “could be preferable.” This is a cohort study, not a trial. We review the full evidence, including later observational data, in Hormone therapy and breast cancer risk.

Blood clots

In the French ESTHER case-control study, oral estrogen was associated with a 4.2-fold increase in venous clots and transdermal estrogen with none. Among progestogens, micronized progesterone showed no association (odds ratio 0.7), while norpregnane-type progestins showed a 3.9-fold increase. These data are part of why micronized progesterone is often paired with an estradiol patch for women in whom clot risk is a concern.

Progesterone on its own for hot flashes and sleep

Progesterone alone is used off-label by some clinicians for women who cannot or prefer not to take estrogen.

• In a randomized trial of 133 healthy postmenopausal women 1 to 10 years past their final period, 300 mg at bedtime for 12 weeks reduced the hot flash score by 10.0 points versus 4.4 on placebo. Nine percent discontinued for side effects, none serious.
• In a 2023 randomized trial of 189 perimenopausal women, 300 mg at bedtime did not significantly reduce the primary hot flash score (difference of 1.5 points, P = 0.22), although the study was underpowered and could not rule out a meaningful benefit. Women on progesterone reported fewer night sweats (P = 0.023) and better sleep quality (P = 0.005). No serious adverse events occurred.

If sleep is your main complaint, read our guide on why perimenopause wakes you at 3 a.m. before assuming a hormone is the answer.

Who should avoid it

• Anyone with a peanut allergy, because of the capsule formulation.
• Anyone with undiagnosed abnormal vaginal bleeding, until it has been evaluated.
• Women with a history of breast cancer, when it is part of estrogen-containing therapy.
• Anyone who must drive or work soon after the dose, until the sedating effect is known.

Questions to ask

• Cyclic or continuous: which schedule fits me, and what bleeding should I expect?
• Is 100 mg nightly enough protection with my estrogen dose?
• If I feel groggy in the morning, what are my options?
• Would a hormonal IUD or a combination patch be a reasonable alternative?

For help finding a clinician comfortable with these choices, see how to find a menopause specialist or our OB-GYN directory.