Factbox on Clenbuterol, a substance banned by the World Anti-Doping Agency.

Three-times Tour de France winner Alberto Contador of Spain tested positive for the substance on July 21, 2010.

* Used to treat breathing disorders as a decongestant and bronchodilator.

* Causes an increase in aerobic capacity, blood pressure and oxygen transportation. It also increases the rate at which fats are metabolised.

* It has also been advertised as a weight loss drug and prescribed, commonly under the name Ventipulmin, for treatment of horses suffering from breathing disorders.

* Features on the 2010 WADA banned substances list as an anabolic agent.

* Athletes who test positive for Clenbuterol can face a two-year suspension.

* Several food contaminations were reported in recent years, especially in Asia.

* In 2008, American swimmer Jessica Hardy voluntarily withdrew from the Beijing Olympics after a positive test for Clenbuterol. Her suspension was cut from two to one year after an arbitration panel said she took the drug inadvertently.

* In March, 2010, Chinese cyclist Li Fuyu tested positive for Clenbuterol and faces a two-year suspension.

* Recent cases of positive tests for the substance include Polish canoeist Adam Seroczynski, British hurdler Callum Priestley and Chinese Olympic judo champion Tong Wen.

Reuters