Side effects can include nausea, headache, blood clots, breast pain, depression, and liver problems.[2] Use is not recommended during pregnancy, the initial three weeks after childbirth, and in those at high risk of blood clots.[2][4] It; however, may be started immediately after a miscarriage or abortion.[4] Smoking while using combined birth control pills is not recommended.[5] It works by stopping ovulation, making the uterus not suitable for implantation, and making the mucus at the opening to the cervix thick.[4]