Drug use is a common problem in many sports competitions today. In both professional and amateur sports, many athletes use drugs that are designed to improve athletic performance. The use of these drugs may have harmful effects on the future health of athletes, but they also give an unfair advantage in athletic competitions. Some of the most widely-used performance-enhancing drugs are called "anabolic steroids." Anabolic steroids are drugs that are very similar to the male hormone, testosterone. These drugs allow athletes to develop larger and stronger muscles, and to increase the intensity of training. For sports that require strength, power, or speed, the use of steroids can provide advantages. In past years, many famous sprinters and weightlifters have been found to have used steroids. However, anabolic steroids have many negative side effects. To give just a few examples, steroids can cause changes in mood, including irritability and anger, and can also cause skin problems such as acne. In men, steroid use can lead to reduction in the functioning of the testicles. In women, steroid use can interfere with menstruation. In both men and women, long-term side effects include an increased risk of some forms of cancer. Another widely-used drug is known as EPO. EPO is a hormone that helps to produce red blood cells, which carry oxygen to the muscles. When taken by athletes who compete in sports that require great endurance, EPO may provide an advantage by allowing the athletes to maintain their speed for a longer time and distance. During 1998, there was a scandal at a famous bicycle race, the Tour de France, when it was found that many of these long-distance cyclists were using EPO to gain an advantage over their competitors. EPO has side effects. For example, it increases the likelihood of developing blood clots, which increase the risk of a stroke or heart attack. One difficulty in preventing the use of performance-enhancing drugs is that it is not always possible to detect the use of the drugs. Tests have been developed to detect the drugs, but new varieties of the drugs are often not detected. Also, athletes who stop using the drugs well before a drug test may avoid being detected. Preventing the use of performance-enhancing drugs in athletes is difficult, but it is important. Most athletes want to compete without using artificial substances that provide easy advantages, and they do not want to risk their health by using these substances. If those athletes are to have a fair chance, it is necessary to prevent other athletes from gaining advantages due to the use of these drugs.