Morocco's Jamel Chatbi withdrew from the final after testing positive in a doping test after the heats.

BBC: Bolt storms through to 200m semis

Last February MacLeod was cleared of failing a previous doping test after he had taken an asthma medicine without permission.

BBC: Lock MacLeod signs for Edinburgh

In February, the Scotland international was cleared of failing a doping test after he had taken an asthma medicine without having the obtained the necessary permission.

BBC: Beattie says Scots behind MacLeod

Officials from the Chinese Olympic Committee have confirmed to the state-run news agency Xinhua that all of the Chinese athletes in the games are currently "clean" and that so far there has been no notice from the IOC about athlete doping test results that are positive or abnormal.

CNN: IOC confirm six athletes test positive

Dr Gerry McCann, a lecturer in sports medicine at the Centre for Exercise Science and Medicine at Glasgow University, said the list of banned substances was so comprehensive that it was highly unlikely that an athlete could take a legal substance, but register a positive result in a doping test.

BBC: Doping: Banned substances

However, following a two-day hearing last month, an independent anti-doping tribunal confirmed the test results, the federation said.

CNN: Hingis banned after positive test

The anti-doping facility being used to test samples during the Olympic and Paralympic Games is to be turned into a medical research unit.

BBC: Legacy for anti-doping centre

It was his second failed drugs test and, under the World Anti-Doping Agency (Wada) code, he should have been given a lifetime suspension.

BBC: Gatlin won the 100m title at the Athens Olympics in 2004

The FAW, like most governing bodies in sport, has a strict anti-doping code that holds a player liable for failing a test, even though he may not have deliberately taken a prohibited substance.

BBC: SPORT | Football | Welsh | Moran given drugs ban

False positives on steroid tests are not unheard of, which is why cycling officials insist that any positive be confirmed by a second test by a lab approved by the World Anti-Doping Agency.

FORBES: Magazine Article

But just days later it was revealed that Sanamacha Chanu, who had won Commonwealth gold in 2002, had failed a drugs test during August's selection trials, suggesting problems with doping still remain.

BBC: Commonwealth Games 2010: Form guide - weightlifting

But the news of his drug test didn't help a sport that's long been tainted by doping.

NPR: Landis Doping Allegations Give Cycling Black Eye