Progesterone: The Hormone and the Medicine

After ovulation, the ovaries produce progesterone during the second half of the cycle. It acts on the uterine lining that has developed under estrogen's influence. When hormone levels fall, the lining is shed as a period.

During perimenopause, ovarian hormone production changes and cycles become less predictable. A symptom such as poor sleep or an irregular period cannot establish a specific progesterone deficiency by itself. The assessment should consider menstrual history, symptoms, medication use, and other possible causes.

Progesterone, progestogen, and progestin

Progestogen is the broader category of medicines with progesterone-like activity. Progesterone is one member. Progestin commonly describes a synthetic drug in that category. Different progestogens are used in HRT and contraception, with different doses, formulations, and evidence.

Systemic estrogen can stimulate the uterine lining and increase the risk of endometrial overgrowth and cancer. A person with a uterus usually needs adequate progestogen protection as part of HRT. Oral micronized progesterone is one way to provide it.

The US Prometrium label specifies prevention of endometrial hyperplasia in postmenopausal women with a uterus receiving conjugated estrogen tablets. It also includes secondary amenorrhea, meaning periods have stopped after previously occurring. Those indications use different schedules.

Prescribers also use progesterone alongside other systemic estrogen regimens. The prescription should explicitly name the drug, strength, treatment days, and reason. A schedule intended for one indication cannot automatically be transferred to another.

After hysterectomy, progesterone is often unnecessary for routine estrogen HRT, although circumstances such as residual endometriosis can alter the plan. Low-dose local vaginal estrogen has different prescribing considerations.

Micronization reduces the size of progesterone particles and improves oral absorption. The hormone remains chemically identical to progesterone produced by the ovaries. Approved oral products can therefore be described as bioidentical.

A compounded or over-the-counter cream should not be assumed equivalent to an approved capsule for uterine protection. ACOG describes limited evidence and variable absorption in custom preparations and recommends approved menopause formulations when suitable products exist.

Ingredient lists matter. The cited Prometrium capsules contain peanut oil and are contraindicated in people allergic to peanuts. Check the dispensed product, since other formulations may use different ingredients. Vaginal and injectable progesterone products used for other indications need their own instructions.

Oral progesterone can cause dizziness and drowsiness. The Prometrium label advises taking the prescribed daily dose at bedtime and being cautious with driving or machinery. Food instructions can differ between products, so follow the actual leaflet.

A cyclic schedule can produce a withdrawal bleed after the progesterone course. Continuous regimens have a different expected pattern. Record bleeding and any symptoms that repeatedly occur on progesterone days.

• Keep the estrogen and progesterone instructions together.
• Use a calendar for a cyclic regimen so each treatment day is clear.
• Tell the prescriber if missed doses or side effects make the schedule difficult.
• Discuss an alternative protective treatment before stopping progesterone while continuing systemic estrogen.

Progesterone prescribed for menopause is not reliable contraception. Ask separately about pregnancy prevention when it is relevant, even if periods are irregular or the regimen changes bleeding.