Oral contraceptive pills are a type of hormonal birth control method that contain synthetic versions of the hormones estrogen and progesterone. These hormones work together to prevent pregnancy in several ways:

Preventing Ovulation
- The primary way that contraceptive pills prevent pregnancy is by preventing ovulation. Ovulation is the process in which an egg is released from the ovary and can be fertilized by sperm. By taking the pill regularly, the hormones in the pill signal to the body that ovulation has already occurred, which prevents the release of an egg. Without an egg, there is no chance of fertilization and pregnancy cannot occur.

Thickening Cervical Mucus
- In addition to preventing ovulation, contraceptive pills also thicken the cervical mucus. The cervix is the opening at the bottom of the uterus that leads to the vagina. Normally, the cervical mucus is thin and watery, which allows sperm to swim through it and reach the egg. However, when a woman is taking contraceptive pills, the hormones in the pill cause the cervical mucus to thicken and become more viscous, making it more difficult for sperm to penetrate and reach the egg.

Altering the Uterine Lining
- Lastly, contraceptive pills can also alter the lining of the uterus. The lining of the uterus is where a fertilized egg implants and grows into a fetus. The hormones in the pill can change the lining of the uterus to make it less hospitable to a fertilized egg, making it less likely that a pregnancy will occur even if an egg is released and fertilized.

By working together in these ways, contraceptive pills are highly effective at preventing pregnancy when taken correctly and consistently.