Most conversations about hormone therapy are really conversations about estrogen. Progesterone gets treated as an afterthought — but it is the part that protects your uterus, the part most likely to cause the side effects that make women quit, and the part where the specific type you are given matters enormously. Here is what it does, which forms exist, and what to do when it does not suit you.

Where we stand: Menova is an independent publication. We sell no hormones, we are not your doctor, and this is general education, not medical advice.

Why progesterone is prescribed at all

If you take estrogen and still have a uterus, estrogen alone stimulates the uterine lining to thicken. Over time, unopposed estrogen raises the risk of endometrial hyperplasia and endometrial cancer. A progestogen prevents that thickening.

That is the whole reason it is there. It is not a supplement or an optional extra — for a woman with a uterus on systemic estrogen, it is the safety component of the regimen, and skipping it is not a shortcut anyone should take.

Two situations where it is generally not needed:

  • After a hysterectomy. No uterus, no lining to protect, so estrogen alone is standard.
  • With low-dose vaginal estrogen, which acts locally — see is vaginal estrogen safe.

Progesterone vs progestin: the distinction that matters

The words get used interchangeably and they are not the same thing.

Micronized progesterone is structurally identical to the hormone your body produces. In the US it is available as an FDA-approved capsule; in the UK and elsewhere it is widely used as well. This is what people usually mean by "body-identical."

Progestins are synthetic compounds — medroxyprogesterone acetate, norethindrone, levonorgestrel and others — that act on progesterone receptors but differ structurally.

Why this matters: much of the risk data that shaped how women think about HRT, including the Women's Health Initiative findings, came from studies using a specific synthetic progestin combined with oral conjugated estrogen. Some observational research has suggested micronized progesterone may carry a more favorable risk profile, particularly regarding breast tissue, though the evidence base is not as strong as randomized trial data and should not be overstated. It is a reasonable thing to ask about rather than a settled fact — the fuller picture is in HRT risks and benefits.

It is also worth knowing that micronized progesterone capsules are formulated in peanut oil, which matters if you have a peanut allergy. Say so.

The forms it comes in

  • Oral capsules, usually taken at night. The most common route, and the drowsiness is used deliberately.
  • The levonorgestrel intrauterine system (a hormonal IUD), which delivers a progestin directly to the uterine lining. Widely used for endometrial protection, and it has the side benefit of reducing heavy bleeding — relevant during perimenopause; see heavy periods in perimenopause.
  • Combined patches, which deliver estrogen and a progestogen together — fewer things to remember.
  • Vaginal micronized progesterone, used off-label in some settings when oral is not tolerated.

Our overview of HRT types and forms covers how these pair with the estrogen side.

Cyclical or continuous?

Two regimens, chosen mainly by where you are in the transition.

Cyclical (sequential) — progestogen for around 10 to 14 days each month. This produces a monthly withdrawal bleed. It is the usual approach in perimenopause, when you are still having periods of your own, because continuous therapy in that setting tends to cause erratic breakthrough bleeding.

Continuous combined — progestogen every day, with the goal of no bleeding at all. This is standard once you are postmenopausal, generally after twelve months without periods. Expect some irregular spotting in the first three to six months while your lining settles; persistent or heavy bleeding after that needs assessment.

Getting the regimen wrong for your stage is one of the most common reasons women think "HRT doesn't work for me" when the problem is scheduling — see your first three months on HRT.

Side effects, and what to do about them

This is where women most often quit, usually unnecessarily. Common effects, mostly in the first weeks:

  • Drowsiness — expected with oral micronized progesterone, which is why it is taken at bedtime. Many women find this genuinely helpful for sleep.
  • Bloating and fluid retention
  • Breast tenderness
  • Low mood or irritability — some women are sensitive to progestogens, and this can feel like severe PMS
  • Headaches
  • Breakthrough bleeding, especially early on

If the mood effects are the problem, that is a specific, actionable complaint rather than a reason to abandon hormone therapy. Options your clinician may consider include switching from a progestin to micronized progesterone, changing the route so less reaches the bloodstream (a hormonal IUD delivers locally), adjusting the regimen, or altering the number of days per cycle. Say exactly what changed and when — "my mood dropped four days after starting the progesterone each month" is far more useful than "HRT made me feel worse."

What progesterone is not

Two claims worth pushing back on:

  • It is not a sleep medication, even though it makes many women sleepy. Prescribing it for that purpose alone is not standard.
  • "Bioidentical" compounded progesterone creams are not equivalent to prescribed micronized progesterone for endometrial protection. Absorption from creams is variable and they are not considered adequate to protect the uterine lining — a genuinely important safety point, covered in compounded versus FDA-approved hormone therapy and bioidentical hormones explained.

When to contact your clinician

  • Bleeding that is heavy, persistent, or starts after a period of no bleeding
  • Any bleeding after twelve months without periods
  • Mood changes that are significant or worsening
  • Calf pain or swelling, chest pain, breathlessness, severe headache, or vision changes — urgent

Questions worth asking

  • Am I on micronized progesterone or a synthetic progestin, and why that one?
  • Is my regimen cyclical or continuous, and does that match where I am in the transition?
  • If the side effects do not settle, what would we change first?
  • Would a hormonal IUD be an option for me?

Bring notes. The free printable visit prep sheet works for a medication review as well as a first appointment, and the free 2-minute self-check gives you a symptom baseline to compare against — no account, not a diagnosis, and your answers never leave your device.

Two things worth reading alongside: over-the-counter "natural progesterone cream" is not established as providing endometrial protection and is not a swap for a prescribed progestogen — see what "estrogen dominance" is pointing at and compounded versus FDA-approved. And if a hormonal IUD is doing this job for you, when does my coil come out covers its expiry.

This article is general education, not medical advice. Do not start, stop, or change the progestogen component of hormone therapy without the clinician who prescribed it — it is there to protect your uterus.

Sources: The Menopause Society, NICE NG23 — Menopause, ACOG, and NHS — HRT.