Progesterone Side Effects Information Progesterone is a steroid hormone that is made mostly by the corpus leteum of the ovaries during ovulation and to a lesser degree by the adrenal glands. It is manufactured naturally by the body from the steroid hormone pregnenolone and is a precursor to other steroid hormones most notably cortisol, testosterone, estrogen and androstenedione. Progesterone is a key contributor to reproductive health and important toward the overall hormonal balance that is necessary for a healthy functioning body. Common progesterone side effects are headache, breast pain and vomiting, abdominal pain, fatigue, constipation, etc. are advised to consider all the possible side effects before starting treatment. Can be determined if a woman has a normal menstrual cycle and then stopped menstruating. During pregnancy, especially during the first trimester, these supplements can help maintain the pregnancy. Progesterone supplements are also prescribed for postmenopausal women during hormone replacement therapy. Hormone replacement therapy (HRT) can cause side effects that may interfere or threaten life . Recommended for women who have stopped having menstrual periods, HRT replaces the hormones normally produced by the ovaries during the childbearing years. After menopause, estrogen or combined estrogen and progesterone is prescribed for women who have no uterus removed. During the reproductive years, combinations of two hormones allow the uterus to shed its endometrial lining in preparation for fertilization. However, if the egg is not fertilized, the lining was poured out in the form of menstrual blood every month.