The classic pill, as well as all other hormone-based contraceptives, works in several different ways. The main mechanism is to block ovulation, so an egg is not released every month. This effect is further amplified by making the environmental conditions unsuitable for both gametes (the egg from the woman and the sperm from the man). How does it do that? On one hand, it makes the mucus of the uterine cervix so thick that it becomes a hostile barrier for the ascent of the sperm to the egg. On the other hand, it thins the endometrium (the lining of the uterine cavity), making it unsuitable for implantation of the egg.
Hormonal contraceptives are the safest methods (with close to 100% efficacy), offering the best possible protection. This is especially true for long-acting reversible contraception (LARC), such as intrauterine devices and subdermal implants.
