More than 100 athletes were caught doping and sanctioned in the months leading up to the London Olympics in a drive to eliminate cheats before they reach the Games, the World Anti-Doping Agency (WADA) said.
WADA chief John Fahey said testers had been out in force in an effort to discourage athletes from using performance-enhancing substances in London.
"In the six months prior to June 19, at least 107 athletes were sanctioned," Fahey told an International Olympic Committee meeting.
"I cannot confirm how many of those would have qualified but had that been their ambition I am pleased to say they are not with us in London."
The Games begin on Friday and run until August 12 although the 'in-competition' testing period started with the opening of the athletes village and the official start of the Olympic period on July 16.
The IOC said on Tuesday there had already been 300 drugs tests since that date with none proving positive.
"These efforts in the lead-up to the Games are bearing fruit," said Fahey. "They (doping offenders) should know that avoiding detection is the smallest (possibility) it has ever been."
There will be around 6,250 samples analysed at the Games, more than any other Olympics, while UK Anti-Doping have also been mandated to test in pre-competition training camps.
There were 20 proven cases of doping at the Beijing Games four years ago, including six horses, down from 26 cases in Athens in 2004.