Other less commonly used chemicals have caught the media's eye recently. St. Louis Cardinals' slugger Mark McGwire has admitted to taking a testosterone-producing pill called Androstenedione (Andro for short) for over a year. Although it is still legal in baseball, Andro is banned by the NFL, Olympics, NCAA and ATP.
Unlike performance enhancers like steroids, Andro (which is available over-the-counter) is a naturally produced adrenal hormone. It is converted in the liver to testosterone, which spurs muscle production. No definitive studies on Andro have shown harmful side effects, but some say the supplements could cause such adverse effects as liver damage and heart problems.
Another popular performance enhancing practice which does not involve chemical additives is blood doping. Highly oxygenated blood is drawn from athletes' bodies several weeks prior to competition and reinjected right before a race or match, allowing greater feats of muscular performance. This leads, however, to dangerously elevated levels of blood hemoglobin, which can cause heart attacks and strokes (several cyclists have died from the practice). High hemoglobin levels are, fortunately, detectable through testing, and the International Olympic Committee now tests for blood doping before selected competitions.