Given aygestin for painful periods. why do they say start day one of period? what happens if i take it on the last day of my period? side effects possible? i only have pain , no heavy bleeding and last only 3-4 days. dont want to add bleeding days?

Aygestin is progesterone and used for both painful or heavy bleeding periods. The progesterone helps decrease menstrual cramping and therefore the pain. The progesterone level normally drops when you have your period and so by taking it starting the first day of your period, the drop is not as much. However, if you take progesterone later, you may bleed or spot when you stop taking it.