Wada has urged caution over detecting drug cheats at the Games
The public's confidence in the Olympic Games has been undermined by drug cheats, the head of the World Anti-Doping Agency (Wada) has said.
John Fahey warned that the public would "desert sport" if they continue to believe it is not clean.
His comments come a week after seven Russian athletes were suspended for alleged doping offences.
Mr Fahey singled out for concern the number of Olympic 100m champions who have subsequently failed drugs tests.
He said that 20 years after the Ben Johnson scandal dominated the Seoul Olympics, the 100m in particular, did not command the public confidence it once did.
"There is suspicion out there in the public, they do not have the same confidence they once had," he said.
"That means we must restore sport to its very essence of the fair play concept.
"In the blue riband event of athletics [100m] a number of offenders have been successful there and I hope and pray we do not have another event of that nature."
We have to restore faith, otherwise we are morally bankrupt and saying to our kids 'fill yourselves up with a mouthful of pills if you want to succeed'
Mr Fahey said Wada was winning the fight against drugs in sport but urged caution ahead of the athletic events at the Beijing Games.
"We have to restore faith, otherwise we are morally bankrupt and saying to our kids 'fill yourselves up with a mouthful of pills if you want to succeed'," he said.
"I don't want my grandchildren to succeed in sport by taking something not natural and not healthy."
Five of the seven suspended Russians - Yelena Soboleva, Tatyana Tomashova, Yulia Fomenko, Darya Pishchalnikova and Gulfiya Khanafeyeva - were bound for Beijing.
In the wake of the suspensions International Olympic Committee (IOC) drugs chief Arne Ljungqvist accused Russia of systematic doping, which team officials have denied.
The Olympics athletics schedule is set to get under way on Friday, 15 August.