Methods of Birth Control Birth control pills are an oral contraceptive for women. They are monophasic, biphasic, or triphasic. Each type contains estrogen and progestin in differing amounts. Monophasic birth control pills maintain the same levels of estrogen and progestin throughout the course, while biphasic pills keep the estrogen level the same while increasing the progestin levels for the last 11 days of the pack, and triphasic pills are designed to mimic the natural menstrual cycle by varying both hormones throughout the pack. Basically the progesterone in birth control pills has an antifertility effect, and also suppre