Why do I have to use back-up even if I’m on the pill?

Patient: Hello. I recently started taking yaz (today the 18th of august is the 7th day im on the pill). i take it everyday at 10am. When does yaz really start being effective? Is it true that it is effective immedialty when you take your first pill within 24 hours of your period? And the brochure that i got says if you start taking the pill the sunday after your period you must use a back up method for a week. Im confused. The internet say different things and the pamphelt taht i got say another thing.

Doctor: Birth control pills, in general, should be started within 5 days from the onset of menstruation. The active pills contai n hormones; the inactive pills are just reminder pills. The hormone containing pills suppress ovulation (ovary releasing an egg). If your period starts today (Day 1), you can start with the active pill (darker colored pills) on Day 1 up to Day 5, not beyond Day 5. Back-up method is always recommended for the first 5-7 days and last 5-7 days of the active pill. Upon starting, the hormone level may not immediately suppress ovulation that’s why backup method is always recommended. It is also noteworthy that sperm cells can live up to 3-5 days within the vagina. For example, if you are taking the 21 day pill and you had sex w/o using condoms on Day 19, sperm cells can still live up to Day 22 (wherein no active pill is taken); when this happens, an egg could get released from the ovary on Day 22, hence the chances of conceiving are high. Always remember that the active pill contains the hormone. If you only have about 3-5 active pills left, use back-up contraception just to be sure. Another thing, perfect use of contraception (taking it at EXACTLY the same time everyday) is ~99% effective; when taken around the same time (1-3 hours apart), it is only 90-95% effective in preventing pregnancy. I do hope I have clarified your unanswered questions and take care always.