Progesterone is an important part of hormone therapy (HT) for some people – but not everyone. Here we explain who needs progesterone and why, along with the different forms of progesterone available for HT.
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 fertilization does not happen, and therefore no pregnancy occurs, progesterone levels drop again – which triggers your period.
Substances that act like progesterone but have slightly different structures are called progestins. Progestins are used in a number of medications. These include contraceptives like the contraceptive pill, hormonal intrauterine devices (IUDs) and the contraceptive injection. Both progesterone and some progestins are used in HT. In this article we will refer to all of them as simply progesterone, because their effects are largely the same.
What happens to progesterone levels in menopause?
During perimenopause, progesterone levels will fluctuate, but eventually decrease. Progesterone levels are consistently low after menopause.
Why do you need to take progesterone with HT?
You might be wondering why you need progesterone as part of your HT. After all, isn’t estrogen enough?
It is true that estrogen can be used alone for hormone therapy in some women who no longer have a uterus. But it is very important to also use progesterone if you still have your uterus.
If used alone, estrogen can cause abnormal thickening and even cancer of the uterine lining or endometrium. Taking progesterone alongside estrogen protects the uterine lining and effectively removes this risk.
The only exception is if you’re using vaginal HT (as a vaginal gel, cream, pessary, or ring). This type of HT doesn’t affect the uterine lining because not much of it is absorbed into the body.
Read more about the different types of HT.
What are the best forms of progesterone for HT?
Using estrogen and progesterone together is known as combined HT.
Progesterone can be supplied as pills, patches, or a hormonal intrauterine device (IUD). Only some brands of IUD can be used to supply progesterone for HT. These are called Mirena and Liletta.
Micronized progesterone is becoming increasingly popular. This progesterone is manufactured from plant extracts and is identical to the progesterone found in the human body. It is available as oral tablets under the brand name prometrium or as a generic in the USA.
Current evidence seems to show that micronized progesterone has lower risks than other, synthetic forms of progesterone. This includes a lower risk of breast cancer and serious blood clots (venous thromboembolism) compared to other progesterones.
What are the side effects of progesterone HT?
Side effects are common with both estrogen 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
See your healthcare provider 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 healthcare provider urgently if you have:
- Vaginal bleeding if it has been over one year since your last period
- Bleeding after sex
- Breast lumps or other changes
- Persistent, bothersome abdominal pain
- Unusual headaches, including headaches that 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 HT?
Like all medications, taking progesterone as part of combined HT comes with certain risks as well as benefits.
Using a combination of estrogen and progesterone for HT causes a small but measurable 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 HT.
This risk falls after stopping HT, and after five years off HT your risk returns to the same level as someone who never took HT.
Combined HT can also be associated with an increased risk of serious blood clots including deep vein thrombosis (DVT) and pulmonary embolism (PE).
Read more about the risks and benefits of HT.
Final word
Progesterone is an important part of HT for people who still have their uterus. If you are struggling with menopause symptoms and would like to explore the option of HT, speak to your healthcare provider.
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, Murad M, 2016, ‘Progesterone vs. synthetic progestins and the risk of breast cancer: a systematic review and meta-analysis’, Systematic Reviews, vol. 5, no. 1
- Hillard T et al, 2017, ‘Management of the Menopause’, ed. London: British Menopause Society, pp. 82-99
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