Two types of hormones, estrogens and progestins, are useful in treating the symptoms of menopause. These hormones may prevent some of the unwanted health problems in postmenopausal women, such as thinning of the bones (osteoporosis). It is unclear whether these hormones also prevent other undesired health problems, such as heart disease, colon cancer, and Alzheimer disease. Estrogens and progestins also have side effects. For example, estrogen increases the risk for gallstones. Gallstones are hard deposits (“stones”) that form in the gallbladder, a small organ that makes substances that help the body digest food. Gallstones can, in some cases, lead to such problems as abdominal pain. When these problems occur, treatment usually involves surgery to remove the gallbladder. It is unknown whether using estrogen and progestin in combination increases the development of gallstones.