.S. regulators on Thursday announced a crackdown on use of the dietary supplement androstenedione, or "andro" -- a performance-enhancing substance made famous by baseball home-run hero Mark McGwire, who used the drug in the late 1990s. The testosterone-producing hormone is not technically a steroid, but acts like one once it is absorbed by the body and is used by both professional and amateur athletes to build muscle and increase athletic performance. "Products containing andro may seem to have short-term benefits, but the science shows us that they create real and significant health risks," Health and Human Services (news - web sites) Secretary Tommy Thompson said at a press conference. Those risks for men include possible impotence, testicle shrinkage and breast enlargement. Women who use it can develop male-like traits, including a deeper voice and added facial hair, as well as abnormal menstrual bleeding. Mike in Brazil Children and teenagers who use andro could face stunted growth or early puberty. Studies have also shown a harmful impact on cholesterol levels and an increased risk for heart disease. 8th street latinas Steroids represent a wide range of different chemical compounds. Anabolic steroids can stimulate muscle growth but are closely regulated. Other types of steroids can be prescribed for some health conditions such as asthma. The U.S. Food and Drug Administration (news - web sites) issued warning letters on Thursday to 23 companies that distribute supplements containing andro, officials said. The FDA's action against andro uses a regulatory technicality that deems it an unsafe "dietary ingredient." Dietary supplements do not have to meet the strict safety standards set for pharmaceuticals before they can be sold.