Progesterone

Progesterone is a hormone your ovaries make. The NHS website says it is produced in the second half of the menstrual cycle, and that your ovaries make it, along with estrogen, until menopause.

It belongs to a family called progestogens. The NHS website says progesterone is the one identical to the hormone your body makes, and micronised progesterone, used in some HRT, is that hormone. The others in the family are synthetic. The different medicines in the family are covered on progesterone types.

Estrogen builds up the lining of the womb through each cycle. Progesterone keeps it in check. The British Menopause Society describes progesterone's job in HRT as opposing estrogen in the womb, which the body does naturally in the second half of each cycle. The NHS website says it stops the lining getting too thick, and that when progesterone stops, the lining is shed, like a period.

What changes around menopause

The NHS website says the amount of progesterone and estrogen your body makes falls as you reach menopause. The researchers behind the STRAW+10 staging system describe the later part of the transition as a time of extreme swings in hormone levels and more cycles in which no egg is released.

Protecting the womb

This is the core idea. The BMS says that taking estrogen on its own, without a progestogen, is linked with a significant rise in the risk of the womb lining overgrowing, a condition called endometrial hyperplasia, and of womb cancer. It cites a 1990s trial, PEPI, in which women given estrogen alone had far more overgrowth than those given a placebo, while women given estrogen with a progestogen showed no significant difference from placebo.

So guidance splits HRT in two. The Pakistan Menopause Society says estrogen alone is given to women who have had a hysterectomy, and women with a womb have progesterone or a progestogen added (section 5.4). See HRT and hysterectomy and menopause.

Two ways it is given

The BMS describes two patterns. In sequential HRT the progestogen is taken for part of each month, which brings a monthly bleed; it says this is usually used around perimenopause. In continuous combined HRT it is taken every day, aiming for no bleeding, usually once periods have stopped. It also says a hormonal coil that releases a progestogen into the womb gives the lining adequate protection.

Body-identical and compounded

The PMS recommendations describe licensed, quality-controlled body-identical hormones, micronised progesterone among them, as recommended (5.10). Compounded, custom-made versions are a different thing. The PMS says the BMS, the International Menopause Society and the PMS itself do not recommend them, because of a lack of regulation, evidence and safety data (5.11). The BMS adds that progesterone creams and gels absorb unpredictably and may not protect the womb. See bioidentical hormones.

Side effects

The NHS website lists changes in your periods, breast tenderness and headaches as common side effects of micronised progesterone, and says these usually improve in the first few months.

It can affect sleep too. The European Menopause and Andropause Society (EMAS) says micronised progesterone taken by mouth may help sleep more than other progestogens. The Menopause Society says it is mildly sedating, so it can make you drowsy.

Some unexpected bleeding is common when HRT starts. The BMS says that for most women, adjusting the progestogen often brings it under control, and that bleeding which carries on beyond four to six months despite that, or whose amount or pattern is a concern, should be checked.

The Pakistan Menopause Society lists persistent unscheduled bleeding on HRT among the reasons for a scan (Table 4). And if you are not on HRT, any bleeding after your periods have stopped needs checking: see bleeding after menopause.