Olympic chief Jacques Rogge has told the BBC that hoping for a drug-free Olympic Games is "naive" and that cheating is "embedded in human nature".
Rogge spoke to the BBC's Inside Sport programme as the re-testing of samples from the Beijing Games is set to begin.
"I think one has to be realistic," said Rogge, president of the International Olympic Committee.
"Drug-free sport in general is Utopia. It will be naive to believe that no-one will take drugs."
He added: "There are about 400m people practising sport on this globe, there are not 400m saints on earth.
"Drugs are there to treat the patients. The problem is that they are abused by athletes"
"You will always need cops and judges and prisons and jails and rules and regulations."
Rogge revealed that the imminent re-testing of samples from the Beijing Games will target insulin, as well as Cera, an advanced version of endurance-enhancing hormone EPO.
"We are going to re-test all the blood samples from Beijing," said Rogge.
"About 980 blood samples will be tested for erythropoietin [Cera], the new EPO test, but also insulin.
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All the samples currently held will be available for testing by any new techniques that emerge between now and the 2016 Games.
"We are keeping the samples for eight years and we are going to re-test them," said Rogge.
"And ultimately the judgement on the Beijing Games will be given in eight years' time, because each time a new scientific test is coming up we are going to re-test."
And asked if the drug-makers will always be one step ahead of the testers, Rogge admitted: "I'd say as an MD myself that I am very glad about that.
"Drugs are there to treat the patients. The problem is that they are abused by athletes."
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