Menopause is the time when a woman's ovaries permanently decrease production of the hormones estrogen and progesterone. This reduction in hormone levels leads to the end of menstruation. In the years around menopause, the changes in hormone levels result in symptoms, including hot flashes, night sweats, mood swings, and vaginal dryness. The lower hormone levels also put women at risk for osteoporosis and heart disease. Postmenopausal hormone replacement therapy (HRT) refers to regimens of the female hormone estrogen with or without progesterone. Hormone replacement therapy reduces the uncomfortable symptoms of menopause. It also influences the development (favorably and unfavorably) of conditions including osteoporosis (thinning of the bones that can lead to fractures), heart disease, stroke, blood clots, dementia, and cancer (colon, breast, and uterine). Before the publication of the results of 2 large studies, the Heart and Estrogen/progestin Study (HERS) in 1998 and the Women's Health Initiative (WHI) in 2002, research suggested that the benefits of HRT outweighed the risks. However, HERS and the WHI, which were of higher quality than previous studies, showed that women taking HRT actually had a higher risk for heart disease and stroke than women not taking HRT. The results of the WHI received substantial media attention.