She started HRT at 51 and felt like herself again within a month. Then, in the second week of every cycle, she turned into someone she did not recognise: tearful, bloated, snapping at everyone, sleeping badly. She assumed HRT was not for her and stopped.
The oestrogen was never the problem. The progestogen was, and there were at least four alternatives she was never offered.
Most conversations about HRT focus on oestrogen: patch, gel or tablet, what dose. The progestogen, the part that protects the womb, is often treated as an afterthought. It should not be. It is the part that most often causes side effects, and the choice affects bleeding, mood, sleep and, according to some studies, breast cancer risk.
If you still have a womb, oestrogen on its own makes the lining, the endometrium, grow. Over time that raises the risk of endometrial hyperplasia and cancer. A progestogen counteracts this by keeping the lining thin.
So if you have a womb and take oestrogen, you need a progestogen. If you have had a hysterectomy, you usually do not, although there are exceptions, for example after some treatments for endometriosis.
Vaginal oestrogen used on its own for dryness is different. It is absorbed in such small amounts that a progestogen is not needed. See vaginal dryness and intimacy.
Micronised progesterone (in the UK, usually Utrogestan). This is chemically identical to the progesterone your ovaries make, made from plant sources. It is taken as a capsule at bedtime: either for part of each month if you still have periods, or every night if your periods have stopped.
Synthetic progestogens, such as norethisterone, medroxyprogesterone acetate, levonorgestrel and dydrogesterone. These are often combined with oestrogen in one tablet or patch, which some women find more convenient.
The hormonal coil (a 52mg levonorgestrel intrauterine system, such as Mirena). This releases a progestogen directly into the womb, so very little reaches the rest of the body. It also provides contraception, which matters in perimenopause, and often makes periods lighter or stop altogether.
If you are still having periods, or your last one was less than about a year ago, HRT is usually sequential: oestrogen every day and a progestogen for part of each month, which produces a regular withdrawal bleed.
Once you are clearly postmenopausal, you can usually switch to continuous combined HRT, where both are taken every day and the aim is no bleeding at all. Irregular spotting is common for the first few months. Bleeding that continues beyond about six months, or starts after a long bleed-free spell, needs to be checked.
The hormonal coil works in either situation, because it does not depend on your cycle.
This is where the choice of progestogen may matter most, and where the evidence needs careful reading.
The largest study comparing types is the French E3N cohort. Fournier and colleagues followed 80,377 postmenopausal women for an average of eight years. Compared with women who had never used HRT:
That is a striking difference, and it is why many menopause specialists now prefer micronised progesterone.
But there are important caveats. This was an observational study, so the women choosing each type may have differed in other ways. Most of the women using micronised progesterone had used it for less than five years. And a very large pooled analysis published in the Lancet in 2019 found that most types of combined HRT were associated with some increase in risk with longer use, although it had limited data on micronised progesterone specifically.
The honest summary: micronised progesterone and dydrogesterone appear to carry a lower breast cancer risk than other progestogens, at least for the first few years, but it would be wrong to say they carry none. The truth about HRT research explains how to put these numbers in context.
Oral oestrogen raises the risk of blood clots; oestrogen through the skin, as a patch, gel or spray, does not appear to. The progestogen matters here too.
In the French ESTHER study, women using transdermal oestrogen with micronised progesterone or pregnane-type progestogens did not show an increased risk of clots, while those using a different group, norpregnane derivatives, did. Those are not commonly used in the UK, but the finding supports the general view that transdermal oestrogen with micronised progesterone is the lowest-risk combination for clots.
Some women are sensitive to progestogens. It tends to show up as premenstrual-type symptoms during the days they take it: low mood, irritability, anxiety, bloating, breast tenderness or acne. Signs of low progesterone and HRT side effects cover the overlap.
If that sounds familiar, the answer is usually to change the progestogen, not to stop HRT. Options a specialist might suggest include:
Never simply stop taking the progestogen while continuing oestrogen, as that leaves the womb unprotected.
Take it at bedtime. It makes many women drowsy, which is why it is often a welcome side effect: some find they sleep better on it.
Take it on an empty stomach or follow the instructions on the pack, as food can change how much is absorbed.
Make sure the dose matches your oestrogen. Higher doses of oestrogen may need more progestogen to protect the womb. If your oestrogen dose has gone up, ask whether your progestogen dose should too.
Unexpected bleeding needs checking. It is often harmless, but it is also how inadequate womb protection shows itself.
Micronised progesterone is body-identical: the same molecule your body makes, licensed, regulated and dose-checked. That is different from compounded "bioidentical" hormones mixed by private pharmacies, which are not licensed and vary in strength. See are bioidentical hormones safe?
Why do I need progesterone with HRT?
If you have a womb, oestrogen alone makes the lining grow and raises the risk of endometrial cancer. A progestogen keeps the lining thin. After a hysterectomy it is usually not needed.
Which progestogen is safest for breast cancer risk?
In the largest comparison, micronised progesterone showed no measurable increase in risk and dydrogesterone only a small one, while other synthetic progestogens showed a clear increase. This was an observational study, mostly of shorter-term use, so it is not a guarantee.
Can the Mirena coil be used for HRT?
Yes. The 52mg levonorgestrel coil can provide the progestogen part of HRT and contraception at the same time. Ask how long yours is licensed for womb protection, as this can differ from its contraceptive lifespan.
Why does HRT make me feel low for part of the month?
That pattern often points to progestogen sensitivity. Changing the type of progestogen, the regimen, or switching to the coil often helps.
Why does Utrogestan make me sleepy?
Micronised progesterone has a sedating effect in many women, which is why it is taken at bedtime. Some find it improves their sleep.
Is bleeding on HRT normal?
A regular bleed on sequential HRT is expected, and irregular spotting is common in the first months of continuous HRT. Bleeding that continues beyond about six months or starts after a bleed-free spell should be checked.
Sources: Fournier A, Berrino F, Clavel-Chapelon F, Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study, Breast Cancer Res Treat 2008;107(1):103-11 · Collaborative Group on Hormonal Factors in Breast Cancer, Type and timing of menopausal hormone therapy and breast cancer risk, Lancet 2019;394(10204):1159-68 · Canonico M et al., Hormone therapy and venous thromboembolism among postmenopausal women: the ESTHER study, Circulation 2007;115:840-5 · National Institute for Health and Care Excellence, Menopause: identification and management (NG23) · Educational only, not medical advice. Do not change HRT without speaking to your prescriber.
Keep reading: HRT side effects · The truth about HRT research · Signs of low progesterone · When to start HRT · HRT checker · Take the free Hormone Quiz