Norethisterone is a progestogen (a drug which acts like the hormone progesterone) which is often used to try to control heavy or painful periods, to try to alleviate pre-menstrual symptoms, or to improve symptoms in endometriosis. Depending on the problem, it may be prescribed to be used from day 5 until day 24 or from day 19 until day 26. Taking norethisterone regularly is likely to prevent you from becoming pregnant.