Hi, OCPs usually contains two types of hormones, estrogens and progestins and, when taken properly, prevents pregnancy. It works by stopping a woman's egg from fully developing each month. The egg can no longer accept a sperm and fertilization is prevented. Although oral contraceptives have other effects that help prevent a pregnancy from occurring, this is the main action... It is very important that your doctor check your progress at regular visits to make sure this medicine does not cause unwanted effects. ..