Progesterone is a female sex hormone produced by the ovaries after ovulation each month. It prepares the lining of the uterus for a possible pregnancy and works in balance with estrogen.
As ovulation becomes irregular in perimenopause, progesterone levels fall, contributing to changes in periods and, for some women, sleep and mood symptoms.
In hormone therapy, a progestogen (progesterone or a similar synthetic) is given alongside estrogen for women who still have a uterus, to protect the womb lining — see our guide to progesterone for menopause.