Progesterone

Progesterone is a hormone your ovaries make naturally, mostly in the second half of the menstrual cycle. Its main job is to prepare and steady the lining of the uterus (the endometrium) after ovulation. As you move through menopause, your ovaries wind down and progesterone levels fall.

The medicine called micronized progesterone is a laboratory-made copy that is molecularly identical to the hormone your body produces, which is why it is often described as "body-identical." It is sold under brand names such as Prometrium and Utrogestan. In menopausal hormone therapy, it is usually combined with estrogen — a pairing also known as hormone replacement therapy (HRT).

How it works: progesterone attaches to progesterone receptors in tissues such as the womb lining. There, it counteracts estrogen's tendency to make the lining grow and thicken, helping to keep it thin and stable.

Body-identical versus synthetic: micronized progesterone shares the exact structure of the hormone you make yourself. Synthetic progestogens — known as progestins, such as medroxyprogesterone acetate or norethisterone — are different molecules designed to behave like progesterone. All of them are grouped under the umbrella term "progestogen," but they can differ in how they feel and in their risk profile. This page is about micronized progesterone.

In midlife care, the most common reason progesterone is prescribed is to protect the lining of the uterus during menopausal hormone therapy. Estrogen eases symptoms such as hot flushes, night sweats and vaginal dryness, but on its own it also stimulates the endometrium to thicken. Left unchecked, this "unopposed" estrogen raises the risk of endometrial hyperplasia and cancer of the womb lining. Adding a progestogen keeps that lining in check. Our guide to progesterone for menopause goes into more detail.

This is why, if you still have a uterus, a clinician will nearly always prescribe progesterone (or another progestogen) alongside estrogen. If you have had a hysterectomy, you usually do not need it, because there is no womb lining to protect. The way the two hormones balance each other is explained in estrogen vs. progesterone.

Progesterone is sometimes prescribed for other reasons too — for example to bring on a period in people with absent periods (secondary amenorrhoea), as part of assisted fertility treatment, or to help steady an erratic cycle during perimenopause. Some people also find it improves their sleep. Whether any of these apply to you is a decision for you and your prescriber.

Progesterone may suit you if you are taking estrogen for menopause symptoms and still have a uterus, if you prefer a body-identical option, or if the calming, sleep-friendly effect of the night-time capsule is welcome. As with any hormone medicine, whether it is right for you is a clinical decision that weighs your symptoms, history and preferences.

There are situations where progesterone is not suitable, or where it needs careful discussion first. Tell your clinician about your full medical history — including any of the following:

• Known, suspected or past breast cancer or other hormone-sensitive cancer
• Unexplained or unusual vaginal bleeding that has not yet been investigated
• A current or past blood clot in a vein (deep vein thrombosis) or lung (pulmonary embolism), or a known clotting disorder
• Recent stroke, heart attack or other arterial disease
• Active liver disease or abnormal liver tests
• Pregnancy, unless progesterone has been prescribed specifically as part of fertility care
• The rare condition porphyria
• Allergy to any ingredient — some progesterone capsules are formulated in peanut (arachis) oil or contain soya, so a peanut or soya allergy matters

This list is not exhaustive, and having one of these does not automatically rule out treatment — it simply means the decision needs more care. Never start, stop or change progesterone on your own; always go through your prescriber.

Progesterone is a prescription-only medicine, and the brand, form and schedule are always chosen by your clinician to fit your situation. The notes below are general background only — follow the exact instructions on your prescription and in the leaflet inside the pack, and take it exactly as prescribed.

The most familiar form in menopause care is an oral soft capsule. It is very often taken at bedtime, because it commonly causes drowsiness. Taking it at night turns that side effect into a possible benefit — some people sleep better — and cuts down on daytime grogginess.

Depending on where you are in the menopause transition, progesterone may be taken every day (a "continuous" pattern, more common once periods have stopped) or for only part of each month (a "cyclical" or "sequential" pattern, more common in perimenopause, which usually triggers a monthly bleed). Your clinician will explain which pattern applies to you. Do not stop suddenly without advice.

Most people tolerate progesterone well, and many side effects ease over the first few months as your body adjusts. Because it is usually taken with estrogen, some effects can be hard to pin on one hormone alone.

If side effects are troublesome or do not settle, tell your prescriber. Sometimes the brand, form, timing or overall regimen can be adjusted — but any change should be made with clinical advice, not on your own.

Serious problems with progesterone are uncommon, but they are important to know about. Much of what we understand about risk comes from large studies of combined estrogen-plus-progestogen hormone therapy rather than progesterone taken alone, and regulators such as the FDA require these medicines to carry prominent warnings.

Combined menopausal hormone therapy has been linked to a small increase in the risk of:

• Blood clots in the veins and lungs (deep vein thrombosis and pulmonary embolism)
• Stroke and, in some studies, heart disease
• Breast cancer, with the level of risk influenced by the type of progestogen and how long therapy is used
• Gallbladder disease

These risks are generally small for most people, and they are weighed against the benefits of treatment; your clinician can help you understand what they mean for you. Any unexpected or ongoing vaginal bleeding should always be reported and investigated, because it can occasionally signal a problem with the womb lining.

Seek urgent medical help if you develop any of these red flags:

• Pain, swelling, redness or warmth in one leg, or sudden chest pain or breathlessness (possible blood clot)
• Sudden weakness or numbness on one side, trouble speaking, or a severe unusual headache or change in vision (possible stroke)
• Yellowing of the skin or eyes, severe upper-abdominal pain, or very dark urine (possible liver problem)
• Signs of a serious allergic reaction — a spreading rash, swelling of the face, lips or throat, or difficulty breathing

Always give your clinician and pharmacist a full list of everything you take, including prescription medicines, over-the-counter products, herbal remedies and supplements. Progesterone is broken down by the liver, so medicines and substances that speed up or slow down those liver enzymes can change how much progesterone is in your system.

• May lower progesterone levels: some epilepsy medicines (such as carbamazepine and phenytoin), the antibiotic rifampicin, and the herbal remedy St John's Wort.
• May raise progesterone levels: certain antifungal and antibiotic medicines (such as ketoconazole), and grapefruit or grapefruit juice.
• Adds to drowsiness: alcohol, sedatives and some other medicines that cause sleepiness — take care with driving or tasks that need full alertness until you know how progesterone affects you.

Some health conditions also call for extra caution or monitoring, including diabetes, epilepsy, migraine, asthma, depression, and heart, kidney or liver disease. Let your prescriber know if you are pregnant, think you might be, or are breastfeeding. None of this means you cannot use progesterone — it means the decision, and any monitoring, should be tailored to you. This is general information and not a substitute for advice from your own healthcare professional.