Progestin is a synthetic hormone used to affect a woman's body in
the same ways as the hormone progesterone. The ovaries produce progesterone
during the second half of the menstrual cycle to help prepare the uterus for
pregnancy. At the time of menopause, the level of progesterone declines.
Progesterone regulates the cyclic growth and breakdown of the
uterine lining (endometrium). When a woman's progesterone levels are low,
progestin can be used to treat endometrial problems such as heavy, irregular
menstrual bleeding. Women with an intact uterus who take estrogen are also
prescribed progestin, which prevents the estrogen from causing cancerous cell
growth in the endometrium.