It's a cat and mouse game between athletes looking to enhance their performance with drugs and the World Anti-Doping Agency (WADA), tasked with testing the athletes and finding any cheats.
Perhaps the most famous drugs-bust in the history of sport was in 1988, when Ben Johnson, winning gold and setting the world record for the 100m sprint at the Barcelona Olympics, was stripped of his title after testing positive for stanozolol.
Years later, it was revealed that the man who won gold in his place, Carl Lewis, had also tested positive for drugs before the Seoul Games but had been allowed to compete anyway.
Since then, drugs controls for international sporting events have gotten ever more stringent, but the drugs have been setting the pace, being designed in ever more complicated and subtle ways to evade checks. Dubbed designer drugs, these are built by modifying the initial drugs in a way that they will avoid being picked up by current checks by the WADA. Other drugs are so commonly used in normal medicine that they may show up without the athlete even knowing they'd taken them.
At the Games, for example, India's Rani Yadav, who came sixth in the 20km walk, tested positive for 19-norandosterone. This can be found naturally in humans and as such could 'avoid' WADA tests, but it can also be coupled with other drugs to have performance-enhancing effects.
Netballer Megha Chaudhary also tested positive for the drug earlier this year, but her ban was waived as it was likely the increased levels of the 19-N were due to contraceptive pills.
Two other athletes have tested positive for methylhexaneamine. Nigerians Samuel Okon came 6th in the 110m hurdles and Osayomi Oludamola won gold in the women's 100m sprint, while Folashede Abugan, also a Nigerian, was part of the 4x400 women's relay team which claimed the silver medal. Are these designer drugs any more dangerous than their 'normal' counterparts?
Yes. Dr Gary Wadler of the New York University School of Medicine was quoted in an ESPN.com interview that, "because they are created in clandestine labs by unlicensed and untrained amateur chemists, they can be extremely dangerous, in many cases more dangerous than the original drug."
Indeed, since 2006 WADA has teamed up with Interpol, the international police organisation, after both recognised the need for stronger legislation in what is seen as a 'high profit, low risk' crime.