Birth control pills are medicine with hormones. They are 99.7% effective in preventing pregnancy when taken on time. So how oral contraceptives work?
The different phases in 28 days menstrual cycle is responsible for preparing the uterus for pregnancy.
The shedding of uterine lining leads to Menstrual bleeding. Once the bleeding ends, Follicle-stimulating Hormone(FSH) and Luteinizing Hormone(LH) will be secreted above their normal levels.
FSH and LH are responsible for thickening of the uterine lining and maturity of egg which leads to ovulation(release of matured egg from ovary).
The goal of oral contraception is to artificially block these two hormones and suppress ovulation.
Birth control pills usually consist of either a single hormone, Progestin or two hormones Progestin and Estrogen.
These hormones suppress the release of FSH and LH and obvioulsly ovulation. If there is no ovulation there will not be any egg hanging around for the sperm to fertilize, so there is no chance for pregnancy.
Even if ovulation occurs Progestin in the pill causes mucus in the cervix to thicken making it more difficult for the sperm to reach the egg.
Apart from preventing pregnancy, birth control pills can reduce the cramping pain caused during menstruation in some women.