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How can oral contraceptives prevent ovulation?

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Diagram of the menstrual cycle showing hormone levels, follicle development, and endometrial changes across 28 days. It highlights menstruation, ovulation, and the follicular and luteal phases, with labeled curves for estrogen, progesterone, FSH, and LH. — menstruation Cyclical changes during a woman's normal ovulatory menstrual cycle.

Oral contraceptives function primarily by utilizing synthetic steroid hormones—typically a combination of estrogen and progestin, or progestin alone—to disrupt the hormonal signals that regulate the menstrual cycle.12

Under normal conditions, the pituitary gland releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which stimulate the ovaries to produce estrogen and trigger ovulation. Oral contraceptives prevent this process through a mechanism known as negative feedback:12

Suppression of Hormones: The synthetic hormones in the pill inhibit the pituitary gland from releasing the necessary levels of FSH and LH.12
Inhibition of Ovulation: Without the surge of FSH and LH, the ovarian follicle does not mature, and the release of a mature egg is prevented.13

Additionally, progestin-only preparations can further reduce the likelihood of pregnancy by thickening the cervical mucus, which creates a barrier that makes it difficult for sperm to reach the egg.12