How do hormonal contraceptives primarily prevent pregnancy?

Hormonal contraceptives primarily prevent pregnancy by preventing ovulation. They achieve this through the administration of synthetic hormones, such as estrogen and progestin, which work together to inhibit the natural hormonal signals that trigger the ovaries to release an egg each month. When ovulation is prevented, there is no egg available for sperm to fertilize, thereby significantly reducing the likelihood of pregnancy.

In addition to preventing ovulation, hormonal contraceptives can also alter the lining of the uterus and change cervical mucus to create an inhospitable environment for sperm and fertilization. However, the key mechanism at work is the suppression of ovulation itself, which is why this answer is the most directly associated with how these contraceptives function.