oral contraceptive (OC), oral hormone medication for contraception. The two major sex hormones in females are estrogens and progestins. When synthetic forms of these hormones are taken, they inhibit the production of gonadotropin-releasing hormone by the hypothalamus; the pituitary therefore does not secrete gonadotropins to stimulate follicular maturation and ovulation. Depending on the formulation, cyclical changes in the uterus, vagina, and breasts may be similar to a normal menstrual cycle. Progestin-only oral contraceptives generally do not block ovulation. Instead they cause the cervical mucus to remain thick, which prevents the entry of sperm into the uterus and fallopian tubes. Seasonale, an extended-cycle method of contraception with menstrual periods every three months, was recently approved by the FDA. Contraindications to the oral contraceptives include pregnancy, diabetes mellitus, liver disease, hyperlipidemia, thrombotic complications, coronary artery disease, and sickle cell disease. Patients with depression and migraine headaches and those who are heavy cigarette smokers need to be followed up more often. The pregnancy rate when oral contraceptives are used correctly is less than 0.2% a year. See also contraception.
