COCPs can provide effective contaception , if the first pill is taken no later than 5 days after the start of menstruation . If the treatment is started at any other time in the menstrual cycle , COCPs can not provide a safe means of contraception for the first 7 days of use . COCPs provide effective contraception from the very first pill if started within five days of the beginning of the menstrual cycle ( within five days of the first day of menstruation ) .