Menstrual stimulants are usually best started on the fifth day of menstrual bleeding. In artificial cycles, oral estrogen and progesterone are taken starting on the fifth day of menstrual bleeding. The pills should usually be taken at a regular time and should not be missed, otherwise withdrawal bleeding will occur. If you are trying progestins to regulate menstruation, you start taking them in the second half of your period and take them orally for 12-14 days to regulate menstruation. If your period is irregular and you have constant bleeding, you can take the pills at any time to regulate menstruation and stop bleeding. If you are over 40 years of age and have recurrent vaginal bleeding with a thick lining, it is best to have a diagnostic curettage before taking menstrual stimulants. In this way, it is certain that the endometrium is not cancerous, and only then can you take pills to regulate menstruation and stop bleeding.