Clenbuterol: What is it?

Like amphetamine or ephedrine, clenbuterol acts as a stimulant, increasing heart rate. In medicine, it is used to treat asthma.

Like some steroids, the drug also has anabolic effects. Athletes and body builders use it to build muscle and burn fat. The drug is banned in sports as a performance enhancer and is readily detectable in urine samples. First-time offenders risk a two-year competition ban.

On Monday, the Court of Arbitration for Sport banned three-time Tour de France champion Alberto Contador for two years and stripped him of his 2010 Tour title after rejecting his claim that a positive test for clenbuterol was caused by eating contaminated meat on a 2010 Tour rest day.

Farmers illegally use clenbuterol to bulk up livestock and produce leaner meat. In China, where its illegal use in farming has been well documented, clenbuterol is nicknamed "lean meat powder.'' Some athletes have tested positive for traces of the drug after eating contaminated meat.

The drug is potentially dangerous and can have nasty side effects for humans. These can include headaches, trembling, nausea, heart palpitations and other poisoning symptoms. There have been numerous documented cases of people seeking hospital treatment after eating meat contaminated with high concentrations of clenbuterol.