Alberto Contador, the 2010 Tour de France winner, had his title taken away Monday after being found guilty of doping, specifically for testing positive for clenbuterol.
The drug is a beta2-agonist that works as a bronchodilator, loosening muscles that line the airways so that air can pass through more easily. It has other properties as well that are attractive to athletes, some of whom use it as a performance-enhancing drug.
Clenbuterol can also increase heart rate, build lean muscle mass and promote weight loss. For those reasons it's been banned by the World Anti-Doping Agency and the International Olympic Committee. Side effects can include nervousness, nausea, headaches and insomnia.
Clenburterol is also used as a veterinary drug but is banned for use in livestock in the U.S., since ingesting meat containing residue of the drug can be harmful to humans. In 1991 the Food Safety and Inspection Service of the USDA said it would condemn meat that tested positive for traces of the drug.