Craig Freudenrich

About the author: Craig Freudenrich is a biomedical researcher and a senior editor of science, medicine, and the human body for the website HowStuffWorks.com.

Many athletes have turned to performance-enhancing drugs to gain a competitive advantage. Performance-enhancing drugs include anabolic steroids for building mass and strength, and protein hormones that increase the amount of oxygen in body tissues, which boosts athletic endurance. Most of these drugs have unpleasant and/or dangerous side effects and have been banned by the International Olympic Committee and other governing athletic agencies. Urine and blood tests are conducted to keep drug users out of athletic competitions, but "masking drugs" are often taken to hide the presence of illegal substances, making detection difficult.

Every two years as the Olympic Games begin, we hear about athletes using or, at least, being tested for performance-enhancing...