Hi & Welcome. Norethisterone is a synthetic progestogen hormone commonly prescribed to treat irregular, painful or heavy periods, endometriosis (a painful condition caused by tissue that usually lines the womb growing outside the womb), premenstrual tension and to postpone the period. To be effective it has to be taken twice daily, three days before the expected day of period and to be continued as long as you wish (maximum for 2 weeks). Once you stop taking this medicine, the withdrawal bleeding occurs within 3 days. Its most common side effects include headache including migraine, backache, bloating sensation, stomach pain, breast tenderness, weight gain, etc. which are tolerable and reversible upon stopping the medicine. Hope this answers your query.