These are birth control pills that contain estrogen and a progestin. They work by preventing ovulation, thickening cervical mucus to keep sperm from entering the cervix, preventing fertilization and making the endometrium thinner to help prevent implantation. The good side effects can include having more regular periods and decreased flow and cramping, less acne, and a decreased risk of ovarian, uterine and colorectal cancers. The bad side effects can include a decrease in a woman’s sex drive, moodiness, and breast tenderness. The typical failure rate has an outrageously large range of between 7% and 30%. The other type of birth control is called the minipill or the progesterone-only birth control pill. It does not contain estrogen.