Progesterone vs progestin: what is the difference in HRT?

Progesterone is the hormone your ovaries make after ovulation; a progestin is a laboratory-made molecule designed to act like it. In menopausal hormone therapy both do the same essential job, protecting the uterine lining from the overgrowth that estrogen alone causes, and both are FDA-approved for it. Beyond that job they differ: observational studies link micronized progesterone to less breast cancer and clot risk than some progestins, but no randomized trial has tested those outcomes head to head.

At a glance

	Micronized progesterone	Synthetic progestins
Molecule	Structurally identical to ovarian progesterone	Modified structures: medroxyprogesterone acetate, norethindrone acetate, levonorgestrel and others
Protects the uterine lining	Yes, when adequately dosed	Yes
Used in the WHI trial	No	Yes (medroxyprogesterone acetate)
Breast cancer with estrogen, French E3N cohort	Relative risk 1.00	Relative risk 1.69
Blood clots, French ESTHER study	No association (odds ratio 0.7)	Depends on the type; 3.9 for one class
HDL cholesterol gain from estrogen, PEPI trial	Largely preserved	Mostly blunted
Practical issues	Drowsiness and dizziness; capsules contain peanut oil	Vary by product
Prevents pregnancy	No	The levonorgestrel IUD does

The vocabulary

“Progestogen” is the family name for anything that acts like progesterone. The Menopause Society’s 2022 position statement divides it into two branches: micronized progesterone, which is structurally identical to the progesterone made by the ovary, and synthetic progestins, including medroxyprogesterone acetate, norethindrone acetate and levonorgestrel. “Micronized” simply means the progesterone is ground into fine particles, which the FDA label says increases how well it is absorbed when swallowed.

The distinction matters because progestins are not one drug. A 2013 review in Endocrine Reviews compared the progestogens used in hormone therapy and found differences in chemical structure, metabolism, potency and effects on other hormone receptors. Its authors concluded there is no “class effect”: what is true of one progestin is not automatically true of another, or of progesterone.

The job they share

Estrogen stimulates the endometrium, the lining of the uterus. Taken alone by a woman with a uterus, it causes hyperplasia, an overgrowth that can lead to cancer. In the PEPI trial, which randomized 875 women aged 45 to 64 for 3 years, 34 percent of women on estrogen alone developed adenomatous or atypical hyperplasia, compared with 1 percent on any of the three estrogen-plus-progestogen regimens, two using medroxyprogesterone acetate and one using micronized progesterone.

Either branch works, provided the dose and schedule are adequate. In the WHI, daily estrogen plus medroxyprogesterone acetate produced an endometrial cancer risk similar to placebo (hazard ratio 0.81). The Menopause Society notes that a systematic review suggested more hyperplasia with micronized progesterone regimens and stresses adequate dosing, for example 200 mg a day for 12 to 14 days a month. Bleeding that starts more than 6 months into treatment should be investigated whichever you take. Dosing schedules are covered in our guide to micronized progesterone.

Where they differ

Breast cancer

The WHI’s breast cancer signal came from estrogen combined with medroxyprogesterone acetate. The best evidence on other progestogens is observational. In the French E3N cohort of 80,377 postmenopausal women followed for a mean of 8.1 years, estrogen with progesterone carried a relative risk of 1.00 (0.83 to 1.22), estrogen with dydrogesterone 1.16, and estrogen with other progestins 1.69 (1.50 to 1.91). The authors concluded progesterone or dydrogesterone “could be preferable.”

Not every source agrees. The Menopause Society describes “some but not all” observational data favoring micronized progesterone and calls for randomized trials. The revised progesterone label notes that a large meta-analysis did not generally find significant differences between estrogen-plus-progestin combinations. Our guide to hormone therapy and breast cancer risk puts these numbers in absolute terms.

Blood clots

The French ESTHER case-control study compared 271 women with a first clot with 610 controls aged 45 to 70. Micronized progesterone showed no association with clots (odds ratio 0.7), nor did the pregnane progestin group (0.9), while norpregnane derivatives were linked to a nearly fourfold increase (3.9). The same study found oral estrogen raised clot odds 4.2-fold and transdermal estrogen did not. The Menopause Society says micronized progesterone is potentially less clot-promoting than other progestins, again without randomized proof. This is one reason the combination of an estrogen patch with micronized progesterone is popular when clot risk is a concern.

Cholesterol

PEPI, a randomized trial, is the clearest head-to-head comparison, although it measured risk factors rather than heart attacks. Over 3 years, HDL (“good”) cholesterol rose 5.6 mg/dL with estrogen alone, 4.1 mg/dL with estrogen plus cyclic micronized progesterone, and only 1.2 to 1.6 mg/dL with the medroxyprogesterone regimens, against a fall of 1.2 mg/dL on placebo. The investigators concluded that for women with a uterus, estrogen with cyclic progesterone had the most favorable effect on HDL.

How they feel day to day

The progesterone label warns of transient dizziness and drowsiness and directs a single dose at bedtime; The Menopause Society notes a mild sedating effect that some women find helps sleep. The capsules contain peanut oil, so a peanut allergy rules them out. Among the common side effects of hormone therapy, which include bloating and breast tenderness, The Menopause Society flags mood swings specifically as progestogen-related. Because the molecules differ, changing the progestogen, its dose or its schedule is a reasonable step when side effects are a problem.

What the label says in 2026

The progesterone label revised in February 2026 no longer carries a boxed warning, part of the FDA change described in Is hormone therapy safe?. Its warnings section still reproduces the WHI’s estrogen-plus-medroxyprogesterone results for clots, stroke, heart disease and breast cancer, and states that their relevance to other products is not known and the risks cannot be excluded. That reflects missing trial data, not evidence of equal harm.

When a progestin is the better fit

• You still need contraception. In perimenopause, a levonorgestrel IUD can protect the lining and prevent pregnancy. The Menopause Society notes it may avoid systemic progestogen side effects, though trial data for this off-label use are limited. See hormone therapy in perimenopause vs after menopause.
• You are allergic to peanuts, which rules out progesterone capsules.
• You want a single patch. Patches that deliver estrogen and a progestogen together use a progestin.

Questions to ask

• Which progestogen are you suggesting, and why for me?
• Is the dose and schedule enough to protect my lining with my estrogen dose?
• Would a levonorgestrel IUD make sense if I still need contraception?
• What bleeding should I expect, and when should I report it?

If you want a clinician who handles these choices routinely, search our OB-GYN directory.