Final answer:
The combined contraceptive pill contains both estrogen and progesterone, which work together to prevent pregnancy by inhibiting ovulation, thickening cervical mucus, and altering the uterine lining.
Step-by-step explanation:
The combined contraceptive pill contains both estrogen and progesterone. These two hormones work together to prevent ovulation, thicken cervical mucus, and create an environment less conducive to fertilization and implantation. The birth control pill is a highly effective method of contraception when used as directed, with a perfect use failure rate of about one percent or less. Despite this, the typical use failure rate is higher, around ten percent, mostly due to inconsistency in pill-taking. Compared to progesterone-only pills, combined oral contraceptives slightly increase the risk of blood clots but reduce the risk of ovarian and endometrial cancers.