Medically reviewed by Dr Rachel Hines, MBChB, MRCGP, DFSRH, DRCOG – Updated 10 July 2024
Progesterone is an important part of hormone replacement therapy (HRT) for some – but not everyone. Here Stella’s clinical advisor Dr Lucy Wilkinson explains who needs progesterone and why, along with the different forms of progesterone available for HRT.
What is progesterone?
Progesterone is a hormone released by the ovaries and the adrenal glands. Its main role is in the menstrual cycle and pregnancy.
Progesterone levels vary throughout your cycle. They rise after an egg is released at ovulation, helping to prepare the uterus for pregnancy by thickening its lining and increasing blood flow to it. If fertilisation does not happen and therefore no pregnancy occurs, progesterone levels drop again – which triggers your period.
Progesterone is used in a number of medications. These include common contraceptives – like the contraceptive pill and the contraceptive injection – and as an important part of HRT.
What happens to progesterone levels in menopause?
During perimenopause, progesterone levels will fluctuate, but eventually decrease over time. Progesterone levels are consistently low after menopause.
Why do I need to take progesterone with HRT?
You might be wondering why you need progesterone as part of your HRT. After all, isn’t oestrogen enough?
It’s true that oestrogen can be used alone for hormone replacement therapy in some women. But it’s very important to also use progesterone if you still have your womb.
This is because if used alone, oestrogen can cause abnormal thickening and even cancer of the womb lining (endometrium). Taking progesterone alongside the oestrogen protects the womb lining and effectively removes this risk.
Progesterone is also given to some people with endometriosis, even if they have had a hysterectomy. There can be tiny areas of endometriosis left after surgery, which can be reactivated by oestrogen – progesterone is given to prevent this from happening.
The only exception is if you’re using vaginal HRT (as a vaginal gel, cream, pessary or ring). This type of HRT doesn’t affect the womb lining because of the type of oestrogen used and the way the hormone stays within the tissues where it is applied.
Read more about the different types of HRT.
What are the best forms of progesterone HRT?
Using oestrogen and progesterone together is known as combined HRT.
Progesterone can be supplied as pills, patches or a hormonal Intrauterine Device (IUD). Also known as ‘coils’, brands of IUD which can be used to supply progesterone for HRT are Mirena, Levosert and Benilexa.
Micronised progesterone is becoming increasingly popular. This is a plant-derived type of progesterone which is identical to the progesterone found in the human body. It’s available as oral tablets under the brand name Utrogestan or Gepretix in the UK and Prometrium in the USA.
Current evidence seems to show that micronised progesterone has lower risks than other, synthetic forms of progesterone. This includes a lower risk of breast cancer and serious blood clots (venous thromboembolism). However, evidence is still emerging and we do not yet know if these medications can be considered ‘breast safe’ or merely generally safer than the other available preparations.
Start your free online menopause assessment to see if HRT is right for you
What are the side effects of progesterone HRT?
Side effects are common with both oestrogen and progesterone, but tend to settle within the first three months of use.
Side effects specific to progesterone include:
- Tender breasts
- Headaches
- Acne
- Mood changes and depression
- Vaginal bleeding
Irregular bleeding is common in the first 4-6 months of starting HRT, affecting up to 40% of women. If you are having frequent or heavy bleeding, see your doctor.
You should also see your doctor if you experience any severe or persistent side effects, or if they persist beyond the first few months of use. They may be able to recommend a change to your prescription or a different way of taking your medication.
See your doctor urgently if you have:
- Vaginal bleeding if it’s been over one year since your last period
- Bleeding after sex
- Breast lumps or other changes (here’s how to check your breasts)
- Severe pain
- Unusual headaches, including headaches which have any associated symptoms like vision changes, dizziness or other sensory changes
- Leg swelling, tenderness or redness
- Other persistent, severe or worrying symptoms
What are the risks of progesterone HRT?
Like all medications, taking progesterone as part of combined HRT comes with certain risks as well as benefits.
Using a combination of oestrogen and synthetic progesterone for HRT causes a small but significant increased risk of breast cancer. For a thousand women using progesterone over a five-year period, an extra four cases of breast cancer will be diagnosed when compared to those not on HRT.
To put this into context, an additional five cases would be diagnosed among those same thousand women if they all drank two or more units of alcohol per day. An additional 24 cases per thousand would be diagnosed if all of the women were overweight or obese.
This risk falls after stopping HRT, and after five years is back to the background risk. Oestrogen-only HRT is not thought to bring an increased risk of breast cancer.
Combined HRT can also be associated with an increased risk of serious blood clots including deep vein thrombosis (DVT) and pulmonary embolism (PE).
Certain types of progesterone – including micronised progesterone and dydrogesterone – may be lower-risk, although evidence is still emerging. It is currently thought that micronised progesterone neither increases nor decreases your risk of breast cancer in the first five years of use.
Read more about the risks and benefits of HRT.
Final word
Progesterone is an important component of HRT for those users who still have their womb. If you are struggling with menopause symptoms and would like to explore the option of HRT, speak to your doctor or take Stella’s free online assessment.
Find out more about menopause on our blog or in our symptoms library.
Asi, N., Mohammed, K., Haydour, Q., Gionfriddo, M., Vargas, O., Prokop, L., Faubion, S. and Murad, M., 2016. Progesterone vs. synthetic progestins and the risk of breast cancer: a systematic review and meta-analysis. Systematic Reviews, [online] 5(1). Available at: https://systematicreviewsjournal.biomedcentral.com/articles/10.1186/s13643-016-0294-5
Hillard, T. et al (2017). Management of the Menopause. ed. London: British Menopause Society, pp. 82-99
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