Amenorrhea has many causes although the most common is pregnancy. Natural causes of amenorrhea include pregnancy, menopause, and breast feeding. Some contraceptives and medication might also interrupt the female menstrual cycle. Lifestyle factors including low body weight, excessive exercise, and stress can lead to a pause in the normal functioning of the menstrual cycle. Typically once the lifestyle issues are addressed, a normal menstrual cycle will resume. Some hormone imbalance disorders can also cause amenorrhea.