Who will win the battle between athletes who use performance-enhancing drugs and the drug testers trying to catch the cheats? (Measured in the number of positive tests)

 (Photo by Tony Duffy/Getty Images)

By Mike Tierney, Special to Universal Sports

For an Olympic athlete in London, the chances are around 50-50. Not for winning a medal or finding fish and chips that aren’t too greasy, but for undergoing a drug test.

Officials project that about half of the 10,500 participants, including all medalists, will be screened for illegal performance enhancers. The dark side of the Games — cheaters versus drug cops — is a never-ending competition because the bad guys (and gals) keep trying to stay one step ahead of the latest steps for detection.

In Beijing, 19 humans were nabbed, along with six horses in the equestrian.  Notorious violators from previous Olympics  include track luminaries Ben Johnson, the world’s fastest (drug-fueled) man in 1988, and Marion Jones, who forfeited her five medals from 2000.

The list of banned substances is much longer than your grocery list — 240, more than ever before. It is updated each year as the testers discover new illicit stuff used for a shortcut to excellence.

Memo to shooters and archers: Avoid that nerve-calming cocktail before taking aim. For them, alcohol is a no-no, at least until the victory toast.

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