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What Is Progesterone?

Progesterone is a naturally occurring hormone involved in the menstrual cycle, preparation of the uterine lining, and maintenance of pregnancy. Prescription progesterone is available in oral capsules, vaginal products, and injectable formulations with different approved indications. Oral micronized progesterone, including Prometrium, is used to prevent endometrial hyperplasia in certain postmenopausal women receiving estrogen therapy and to treat secondary amenorrhea. Other progesterone products are used in selected fertility treatment settings. Progesterone should not be confused with all synthetic progestins, which can have different properties and indications.

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What Is Progesterone?

Progesterone is a naturally occurring hormone involved in the menstrual cycle, preparation of the uterine lining, and maintenance of pregnancy. Prescription progesterone is available in oral capsules, vaginal products, and injectable formulations with different approved indications. Oral micronized progesterone, including Prometrium, is used to prevent endometrial hyperplasia in certain postmenopausal women receiving estrogen therapy and to treat secondary amenorrhea. Other progesterone products are used in selected fertility treatment settings. Progesterone should not be confused with all synthetic progestins, which can have different properties and indications.

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How Does Progesterone Work?

Progesterone binds to progesterone receptors in reproductive tissues and influences hormone-responsive cellular activity. During the menstrual cycle, it helps transform the estrogen-stimulated uterine lining into a secretory lining that can support implantation. When used with estrogen therapy in women with a uterus, progesterone helps reduce the risk of excessive endometrial growth. Its effects can also support certain reproductive processes when administered through approved fertility-related formulations. Progesterone can cause sleepiness and dizziness, especially after oral administration. Its clinical action depends on the formulation, dose, and reason for treatment.

What Conditions Does Progesterone Treat?

Oral micronized progesterone capsules are approved to prevent endometrial hyperplasia in postmenopausal women with a uterus who take conjugated estrogen tablets. They are also approved for secondary amenorrhea, which involves the absence of menstrual periods after menstruation has previously occurred. Certain vaginal progesterone products are used for luteal support in assisted reproductive technology or selected infertility-related conditions. Injectable progesterone has separate indications. A clinician evaluates pregnancy status, unexplained bleeding, hormone history, and clotting or cancer-related risks before prescribing treatment.

How Should Progesterone Be Taken or Used?

Progesterone dosing depends on the product and indication. For prevention of endometrial hyperplasia, Prometrium capsules are commonly taken as 200 mg orally at bedtime for 12 days during each 28-day cycle while estrogen therapy continues. Treatment of secondary amenorrhea may involve 400 mg orally at bedtime for 10 days. Vaginal progesterone preparations follow separate application schedules, while injections require product-specific instructions. Oral capsules should be swallowed as directed. Some progesterone capsule formulations contain peanut oil and must not be used by patients with peanut allergies. Patients should follow the exact formulation prescribed.

What Are the Side Effects and Warnings of Progesterone?

Common adverse effects of oral progesterone include dizziness, sleepiness, breast tenderness, headache, bloating, and changes in vaginal bleeding. Some patients experience mood changes or fatigue. Progesterone capsules used with estrogen therapy carry warnings concerning cardiovascular events, breast cancer, and probable dementia based on hormone therapy findings. Contraindications can include unexplained genital bleeding, certain hormone-sensitive cancers, active or previous blood clots, and liver disease. The risks vary by formulation and treatment setting. Patients should report unexplained bleeding, chest pain, sudden visual disturbances, or severe allergic reactions.

Common Questions About Progesterone

Is progesterone the same as progestin?

Progesterone is a naturally occurring hormone and can also be prescribed as a medication. Progestins are a broader group of progesterone-like compounds, including synthetic medications with different properties.

Can progesterone help regulate menstrual bleeding?

Yes. Certain progesterone regimens are approved for secondary amenorrhea and can cause withdrawal bleeding after treatment. The appropriate treatment depends on the cause of absent periods.

Why is progesterone prescribed with estrogen?

In postmenopausal women with a uterus, oral progesterone can help reduce the risk of endometrial hyperplasia associated with estrogen treatment.

Can progesterone cause drowsiness?

Yes. Oral progesterone can cause dizziness and sleepiness. Certain capsule regimens are taken at bedtime to reduce the impact of these effects.

References

DailyMed - PROGESTERONE capsule. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=d8bcc439-c21d-4eeb-9159-f51e0c60bd70. Date Accessed November 2, 2026.

Progesterone. MedlinePlus. https://medlineplus.gov/druginfo/meds/a604017.html. Date Accessed November 2, 2026.

Progesterone. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Progesterone. Date Accessed November 2, 2026.

Progesterone Vaginal. MedlinePlus. https://medlineplus.gov/druginfo/meds/a604017.html. Date Accessed November 2, 2026.

Progesterone. Drugs and Lactation Database (LactMed). https://www.ncbi.nlm.nih.gov/books/NBK501345/. Date Accessed November 2, 2026.