Hi, Regesterone is the man made alternative to the natural hormone called progesterone. Progesterone and estrogen are the two important hormones regulates the menstrual cycle. Menstrual cycle is the process of egg formation, release and fertilized and gets implanted into the uterine endometrium that is the inner layer of the womb or unfertilized causing menstruation. Menstruation is the process where the inner layer of the womb sheds along with the developed blood vessels, if the egg is unfertilized. Progesterone is the hormone that helps in uterine endometrial development and regulating the menstrual cycle. Norethisterone in Regesterone helps to regulate the cycle, thereby reduces cramps during periods and prevents excess bleeding. Side effects of the drug are headache, dizziness, nausea, breast tenderness, abdominal pain, vaginal spotting, etc. When any of the symptoms is affecting your normal life, visit the gynecologists for alternative medicine. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Pradeepraj, General & Family Physician