Oral Contraceptives

Oral contraceptives contain progestin with or without estrogen, which prevents pregnancy by stopping ovulation (that is, the release of eggs by the ovaries). Oral contraceptive dispensers usually include a 28-day supply: 21 active tablets and 7 inactive tablets for use during the menstrual cycle.

(From KS Saladin, Anatomy and Physiology, 1998, WCB McGraw-Hill, p. 1020; with permission. © The McGraw-Hill Companies, Inc./Bob Coyle, photographer)