An anabolic steroid is any of a group of hormones that stimulate the growth of tissue. Synthetic versions are used in medicine to treat osteoporosis in older women and some types of anemia; they may also be prescribed to aid weight gain in the elderly, sick, or in severely ill patients. These drugs are associated with a number of side-effects, including acne, fluid retention, liver damage, and masculinization in women. Some athletes, such as sprinters and weight-lifters, have been known to abuse anabolic steroids in order to increase muscle bulk.