Progesterone is administered along with estrogen for women undergoing peri-menopause. It may help contribute to the relief of menopausal and may enhance well-being, energy, and libido. Progesterone is given with estrogen to women who have not undergone hysterectomy to balance the effects of estrogen on the uterine endometrium and reduce the risk of unopposed endometrial stimulation. In a study of 50,000 postmenopausal women followed for an 5.8 year study period it was discovered that bioidentical progesterone decreased the risk of breast cancer (RR= 9; P <.001) while synthetic progestin use increased the risk of breast cancer (RR = 1.4).