An overview of oral contraceptives: mechanism of action and clinical use.

Hormonal contraception is available in oral contraceptive pills and in newer formulations, including the transdermal patch, the vaginal ring, subcutaneous implants, and IM injections. Prevention of pregnancy is achieved by inhibiting ovulation, fertilization, and/or implantation of an egg. Hormonal contraception provides effective, tolerable, and reversible prevention of pregnancy. Efficacy and safety profiles are similar for different formulations and administration routes. Lowest expected failure (i.e., method failure) rates for hormonal contraceptives, regardless of formulation, are <2%. Typical failure rates for oral formulations range from <3% to 5% due to failures in compliance. The most commonly reported adverse effects are weight gain, nausea, variations in menstrual flow, breast changes such as tenderness, discomfort, or swelling, depression or mood disturbances, decreased sexual desire or response, and acne. Rare but serious potential effects include cardiovascular diseases, such as stroke, and an increased risk for breast cancer, liver tumors, and gallbladder disease. Hormonal contraceptive use should be avoided in women at risk for blood clots, by heavy smokers, and in women with breast or other cancers. Use of hormonal contraception in adolescents requires special consideration, in part because of decreased compliance.