Final answer:
Oral contraceptives primarily work by suppressing the process of ovulation due to the effects of synthetic estrogen and progestin hormones. These birth control pills also alter the uterine lining and cervical mucus to prevent fertilization and implantation.
Step-by-step explanation:
Oral contraceptives work by suppressing ovulation, which is the release of an egg from the ovaries. The pill contains hormones estrogen and progestin which maintain constant levels in the body, providing negative feedback to the hypothalamus and pituitary gland. This action prevents the release of hormones called follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that are necessary for ovulation. By doing so, oral contraceptives effectively prevent pregnancy.
In addition to inhibiting FSH and LH, the combined pill also causes changes in the lining of the uterus and thickens the cervical mucus. These changes make it more difficult for sperm to reach the egg and for a fertilized egg to implant itself in the uterus. Progesterone-only pills, on the other hand, mainly work by thickening the cervical mucus and thinning the uterine lining, although they also suppress ovulation to some extent. Both methods of hormonal birth control are highly effective when taken as directed.