Combined oral contraceptives (estrogen-progestin)

Combined oral contraceptives (COCs) are prescription medications that contain both an estrogen, most commonly ethinyl estradiol, and a synthetic progestin. They are taken orally, usually in 21–24 days of active pills followed by a short hormone-free interval, and are designed primarily to prevent pregnancy by stabilizing and overriding the normal menstrual hormone cycle. Modern formulations use relatively low estrogen doses and a variety of progestins to balance contraceptive efficacy with safety, bleeding control, and tolerability. COCs work mainly by suppressing ovulation. The progestin component exerts negative feedback on the hypothalamus and pituitary, dampening gonadotropin-releasing hormone pulses and reducing secretion of follicle-stimulating hormone and luteinizing hormone, thereby preventing development and release of a dominant follicle. Progestin also thickens cervical mucus, reduces tubal motility, and causes a thinner, less receptive endometrium, making it harder for sperm to reach the ovum and for implantation to occur. The estrogen component further suppresses follicular development and helps stabilize the endometrium, improving cycle control and reducing unscheduled bleeding. Beyond contraception, COCs are widely used in healthy women to regulate menstrual cycles, reduce heavy or painful periods, improve acne, and suppress cyclical symptoms such as premenstrual syndrome and menstrual migraines. Long-term use is associated with substantial reductions in risk of ovarian and endometrial cancer and can decrease the likelihood of iron-deficiency anemia by lowering menstrual blood loss. However, they also carry risks, including increased risks of venous thromboembolism and certain hormonally related cancers, and they cause predictable changes in lipid, carbohydrate metabolism, and blood pressure that are important in risk assessment.