Alesse is used as contraception to prevent pregnancy. It contains a combination of female hormones that prevent ovulation.
Oral contraceptives come in a variety of formulations. The main division is between combined oral contraceptive pills, containing both synthetic estrogens and progestogens (progestins), and progestogen only pills (mini-pills). Combined oral contraceptive pills also come in varying types, including varying doses of estrogen, and whether the dose of estrogen or progestogen changes from week to week. Combination pills usually work by preventing a woman's ovaries from releasing eggs (ovulation). They also thicken the cervical mucus, which keeps sperm from joining with an egg. The hormones in combination and progestogen-only pills also thin the lining of the uterus. This could prevent pregnancy by interfering with implantation of a blastocyst.
Contributions by Terrace4, Davidruben, and Malkin.