Progesterone

Key facts

• Progesterone is a natural sex hormone, available as tablets, capsules, gels, or vaginal inserts. Brand: Prometrium (micronized progesterone).
• It treats absent or irregular periods, sustains early pregnancy after fertility treatment, protects the uterine lining during estrogen therapy, and eases menopause symptoms as part of hormone replacement therapy (HRT).
• Any unexplained vaginal bleeding must be checked before you start progesterone, and reported straight away if it happens while you are taking it: it can be a sign of a uterine condition that progesterone would otherwise mask.
• Progesterone, especially combined with estrogen, raises the risk of blood clots. Seek urgent care for calf swelling and pain, sudden breathlessness or chest pain, or sudden vision changes.

What progesterone treats

Progesterone treats secondary amenorrhea (periods that have stopped) caused by low natural progesterone, and it helps sustain the uterine lining in early pregnancy after assisted-reproduction procedures. In women taking estrogen for menopause symptoms, progesterone is added to protect the uterine lining from overgrowth and reduce the risk of endometrial cancer. It is also used as part of combined hormone replacement therapy for hot flashes and night sweats.

How progesterone works

Progesterone binds to receptors in the uterine lining, converting it from a growth phase into a stable, secretory state. This sustains early pregnancy and offsets the stimulating effect of estrogen on the lining. Oral micronized progesterone also has a mild calming, sleep-promoting effect on the brain.

Before you take it

• Avoid progesterone if you have undiagnosed vaginal bleeding, a history of blood clots (deep vein thrombosis or pulmonary embolism), certain hormone-sensitive cancers, severe liver disease, or a previous stroke or heart attack.
• Tell your prescriber if you smoke, are significantly overweight, or are immobile for long periods, since these all add to clot risk.
• Migraine with aura, diabetes, and a history of depression need extra caution and monitoring.

Side effects

Common effects include drowsiness (with oral forms, usually taken at night), bloating, breast tenderness, headache, mood changes, and spotting.

Stop and seek urgent medical care for any of these:

• Leg swelling or pain (possible blood clot).
• Sudden breathlessness or chest pain.
• Sudden severe headache or vision changes.
• Yellowing of the skin or eyes.
• Unexplained vaginal bleeding.

Safety essentials

• Report any unexplained vaginal bleeding immediately: it needs assessment before you start progesterone and at any point during treatment.
• Know the signs of a blood clot (leg swelling and pain, breathlessness, chest pain) and treat them as a medical emergency, especially if you smoke or are overweight.
• Oral micronized progesterone is usually taken at bedtime because of its drowsiness effect; do not drive until you know how it affects you.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.