What is the primary mechanism of action of combined oral contraceptives?

Combined oral contraceptives (COCs) primarily function by preventing ovulation and thickening cervical mucus. The mechanism starts with the hormonal components of the pill—estrogen and progestin—working together to inhibit the release of luteinizing hormone (LH) from the pituitary gland, which is essential for ovulation. When ovulation is suppressed, the ovaries do not release an egg, which prevents potential fertilization.

Additionally, the progestin component contributes to thickening the cervical mucus, making it more viscous and less permeable to sperm, further reducing the likelihood of fertilization. This dual-action approach not only offers effective contraception but also contributes to menstrual cycle regulation and can alleviate symptoms associated with menstruation for some users.

While additional actions include regulation of menstrual cycles and effects on the endometrial lining, the primary efficacy in preventing pregnancy essentially revolves around the prevention of ovulation and the alteration of cervical mucus. Therefore, the correct answer highlights the most significant mechanisms through which combined oral contraceptives exert their contraceptive effects.