?A former Olympic champion who had admitted to doping killed himself and reigning Beijing Games winners were disgraced by doping scandals in 2010.

Former Olympic sprinter Antonio Pettigrew was found dead in the back seat of his locked car in August and police announced the 42-year-old committed suicide.

The assistant track coach at the University of North Carolina admitted to doping in 2008 and was stripped of the gold medal in the men's 4x400m relay in 2000 Sydney Games.

He said then that he wanted "to play a role in teaching people, especially young athletes, to know that the negatives far, far outweigh the benefits these substances may give you."

No one knows that how much the American's repentance and revelation would work for the youth but as International Olympic Committee president Jacques Rogge put it, "Doping will never completely disappear from sport because cheating is inevitably a human nature. Our duty is to reduce to as low as possible."

One of the ways to hinder drug cheats is doping tests in which several renowned athletes were found positive for banned substances.

American 400m Olympic champion LaShawn Merritt received a 21-month ban for anabolic steroid dehydroepiandrosterone (DHEA) which he claimed was contained in an over-the-counter product to enlarge his private part while world and Olympic 100-meter champion Shelly-Ann Fraser of Jamaica was suspended for six months after failing a doping test. She said she took a painkiller because of a toothache before her Diamond League race in May in Shanghai.

China's judo Olympic winner Tong Wen was found positive for banned steroid clenbuterol, which she blamed food contamination.

Also blaming food containing the weight-loss and muscle-building clenbuterol was three-time Tour de France winner Alberto Contador of Spain, who tested on July 21 and the analysis of that sample revealed traces of the banned steroid.

The World Anti-Doping Agency (WADA) rejected Contador's claims that his positive test was caused by contaminated meat bought in Spain. WADA even cited a European Union study from 2008 in which experts tested 300,000 meat samples but found evidence of the possible use of clenbuterol in only one of those.

In the meanwhile, American cyclist Floyd Landis, stripped of his 2006 Tour de France title for doping, told media that the use of clenbuterol is widespread in cycling, in one of his many striking remarks which included his attacks on seven-time Tour de France winner Lance Armstrong.

Landis previously alleged that Armstrong and members of their former U.S. Postal team systematically doped and Armstrong has always denied doping.

Many and explosive as the positive cases were, anti-doping experts considered it a proof of their effective work.

"I want to reiterate that zero tolerance does not mean zero positive case. On the contrary, positive cases prove that the system is working since drug cheats will always exist," said China Anti-Doping Agency deputy head Zhao Jian.

Including China, many countries and regions, under the unified anti-doping regulation World Anti-doping Code, moved to crack down on doping with more stringent measures apart from traditional drug tests.

Italian Francesco De Bonis became the first cyclist to be given a doping ban because of discrepancies in his biological passport.

Unlike conventional tests, which can detect the presence of a banned substance, the biological passport monitors swings in blood parameters that may indicate manipulation.

The ground-breaking biological passport system, which was pioneered by cycling's world governing body UCI in 2008, may become a strong weapon to catch drug cheats even if they have never been tested positive.

?A former Olympic champion who had admitted to doping killed himself and reigning Beijing Games winners were disgraced by doping scandals in 2010.

Former Olympic sprinter Antonio Pettigrew was found dead in the back seat of his locked car in August and police announced the 42-year-old committed suicide.

The assistant track coach at the University of North Carolina admitted to doping in 2008 and was stripped of the gold medal in the men's 4x400m relay in 2000 Sydney Games.

He said then that he wanted "to play a role in teaching people, especially young athletes, to know that the negatives far, far outweigh the benefits these substances may give you."

No one knows that how much the American's repentance and revelation would work for the youth but as International Olympic Committee president Jacques Rogge put it, "Doping will never completely disappear from sport because cheating is inevitably a human nature. Our duty is to reduce to as low as possible."

One of the ways to hinder drug cheats is doping tests in which several renowned athletes were found positive for banned substances.

American 400m Olympic champion LaShawn Merritt received a 21-month ban for anabolic steroid dehydroepiandrosterone (DHEA) which he claimed was contained in an over-the-counter product to enlarge his private part while world and Olympic 100-meter champion Shelly-Ann Fraser of Jamaica was suspended for six months after failing a doping test. She said she took a painkiller because of a toothache before her Diamond League race in May in Shanghai.

China's judo Olympic winner Tong Wen was found positive for banned steroid clenbuterol, which she blamed food contamination.

Also blaming food containing the weight-loss and muscle-building clenbuterol was three-time Tour de France winner Alberto Contador of Spain, who tested on July 21 and the analysis of that sample revealed traces of the banned steroid.

The World Anti-Doping Agency (WADA) rejected Contador's claims that his positive test was caused by contaminated meat bought in Spain. WADA even cited a European Union study from 2008 in which experts tested 300,000 meat samples but found evidence of the possible use of clenbuterol in only one of those.

In the meanwhile, American cyclist Floyd Landis, stripped of his 2006 Tour de France title for doping, told media that the use of clenbuterol is widespread in cycling, in one of his many striking remarks which included his attacks on seven-time Tour de France winner Lance Armstrong.

Landis previously alleged that Armstrong and members of their former U.S. Postal team systematically doped and Armstrong has always denied doping.

Many and explosive as the positive cases were, anti-doping experts considered it a proof of their effective work.

"I want to reiterate that zero tolerance does not mean zero positive case. On the contrary, positive cases prove that the system is working since drug cheats will always exist," said China Anti-Doping Agency deputy head Zhao Jian.

Including China, many countries and regions, under the unified anti-doping regulation World Anti-doping Code, moved to crack down on doping with more stringent measures apart from traditional drug tests.

Italian Francesco De Bonis became the first cyclist to be given a doping ban because of discrepancies in his biological passport.

Unlike conventional tests, which can detect the presence of a banned substance, the biological passport monitors swings in blood parameters that may indicate manipulation.

The ground-breaking biological passport system, which was pioneered by cycling's world governing body UCI in 2008, may become a strong weapon to catch drug cheats even if they have never been tested positive.