Doping classes include stimulants (amphetamines, caffeine, clenbuterol, cocaine, and sympathomimetics), narcotic analgesics, anabolic-androgenic steroids, beta-blockers, diuretics, growth hormones, blood, and erythropoietin. Stimulants are used by athletes to reduce fatigue and to increase alertness, response time, and strength. Narcotic analgesics act on the central nervous system to depress fear, anxiety, concentration, and pain sensation. Anabolic-androgenic steroids are testosterone derivatives that exert anabolic (tissue building) and androgenic (masculinizing) influences on the body. Beta-blockers are common used in conditions affecting the cardiovascular system, and they act primarily to decrease heart rate, cardiac output, stroke volume, and mean arterial pressure. In sporting events, beta- blockers are used when a calming effect is required. Athletes can benefit from the use of diuretics in two primary ways, to lose body fluid to rapidly decrease weight and to increase urine production at times when individuals are likely to undergo drug testing. Growth hormones are used to increase the size and strength of muscles, red blood cell infusion will improve an athlete's performance in endurance events, and erythropoietin provides the same benefits as blood doping. Since athletes will always seek advantage over their opponents given the competitive nature of sports, physicians should remain vigilant for signs of doping. 59 references and 1 table