Traditionally , COCPs are packaged with 21 active ( hormone - containing ) pills and 7 placebo pills .
When a woman takes COCP , the hormones in the pills prevent both ovulation and shedding of the endometrium ( menstruation ) .
Traditionally , COCP are packaged with 21 active ( hormone - containing ) pills and 7 placebo pills .
When a woman takes COCP , the hormones in the pills prevent both ovulation and shedding of the endometrium ( menstruation ) .