What is withdrawal bleeding?

Answer 1

Withdrawal bleeding refers to the bleeding that occurs in someone using oral contraceptives during the week that she is taking inactive/placebo pills -- this is when the woman taking the pill menstruates.

Unlike normal menstruation, it is not caused by the natural cycling of hormones that surrounds ovulation, causing the lining of the uterus to be built up (for implantation of a fertilized egg) and eventually shed; rather, it is caused by suddenly taking away an external source of estrogen, which causes the uterine lining to be sloughed off.