Oral contraceptives come in a variety of formulations. The main ivision is between combined oral contraceptive pills, containing both estrogen and synthetic progestogens (strictly progestins, the term used in the United States, but the former term is used in the United Kingdom), and progestogen only pills (mini-pills). Combined oral contraceptive pills also come in varying types, including varying doses of estrogen, and whether the dose of estrogen or progestogen changes from week to week.