Oral contraceptives mimic the action of ovarian hormones. Once ingested, they inhibit the release of gonadotropin-releasing hormone from the hypothalamus, thereby inhibiting the release of pituitary hormones that stimulate ovulation. Oral contraceptives also affect the lining of the uterus and cause cervical mucus to thicken, making it impermeable to sperm. If used consistently and correctly, they are an effective form of contraception. Oral contraceptives can be started at any time in a woman’s life and continue until menopause. Oral contraceptives can be a combination of the hormones estrogen and progestin or contain only progestin. With most combined oral contraceptives, the active tablet (of estrogen and progestin) is taken daily for 21 to 24 days. An inactive tablet (placebo) is then taken daily for 4 to 7 days to allow menstruation to occur. In some products, the placebo pill contains iron and folic acid. Combined contraceptives are also available as extended-cycle products (with 84 active pills, one for each day, followed by 7 days of placebo pills) or as continuous-use products (active pills every day, no placebo pills). Most combined contraceptives contain 10 to 35 mcg of ethinyl estradiol. This dose is considered low. Low doses are generally preferred over high doses (containing 50 mcg of estrogen) because they are equally effective and have fewer side effects, except for a higher incidence of irregular vaginal bleeding during the first few months of use. Estradiol valerate can be used instead of ethinyl estradiol. All combined contraceptives have similar efficacy. The pregnancy rate after 1 year is 0.3% with perfect use and about 9% with inconsistent use. However, combined contraceptives should be used with caution in some women. Their use is contraindicated in: Less than 21 days postpartum or less than 42 days postpartum if the risk of venous thromboembolism is high. Smoking more than 15 cigarettes/day in women over 35 years of age. Current or past history of breast cancer. Severe decompensated cirrhosis, hepatocellular adenoma or liver cancer. Venous thromboembolism (deep venous thrombosis or pulmonary embolism), systemic lupus erythematosus with unknown or positive antiphospholipid antibody status. Migraine with aura or migraine of any type in women over 35. Hypertension, ischemic heart disease, valvular heart disorders. Diabetes with a history of more than 20 years or with vascular disease (eg neuropathy, nephropathy, retinopathy). Current or medically treated gallbladder disease or history of contraceptive-related cholestasis. Elevated triglyceride levels. Acute viral hepatitis. To be effective, progestin-only contraceptivesshould be taken at the same time of day, every day. No placebo tablets are included. They provide effective contraception primarily by thickening the cervical mucus and preventing sperm from passing through the cervical canal and endometrial cavity to fertilize the egg. In some cycles, these contraceptives also suppress ovulation, but this effect is not the main mechanism of action. Common side effects include vaginal bleeding outside of menstruation. Progestin-only oral contraceptives are usually prescribed when women wish to take oral contraception but estrogen is contraindicated. Bibliography: Oral Contraceptives – Gynecology and Obstetrics – MSD Manual Professional Edition (msdmanuals.com)