Final answer:
Oral contraceptive pills work by providing a constant level of hormones, which suppresses ovulation by preventing the release of FSH and LH, and by creating an endometrial environment that is less receptive to implantation.
Step-by-step explanation:
The mechanism of action of oral contraceptive pills is to suppress ovulation. These pills typically contain a combination of estrogen and progestin. By maintaining a constant level of these hormones, they negatively feedback on the hypothalamus and pituitary, preventing the release of Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). Without the surge of LH, ovulation does not occur, and without FSH, follicles do not mature. Moreover, contraception is supported by some endometrial effects; while estrogen in the pills does lead to some thickening of the endometrial lining, this is less than in a normal cycle, making the environment less receptive to implantation.