IAAF president Lord Coe says he cannot guarantee next month’s World Athletics Championships will be drug free.
Russia’s athletics federation is banned from the event in London, having been suspended by the sport’s global governing body in 2015 amid allegations of state-sponsored doping.
“It’s a very utopian view, people will always seek to cheat,” said Coe, speaking on BBC One’s Andrew Marr Show.
Coe, however, added the system for detecting cheats “is a lot safer”.
“We have the technology that allows us to be very much more specific about what we are looking for,” he said.
“I would love to tell you that we will have a drug-free sport in future. Everything we are doing is engaged in trying to achieve that but we know a few people will cheat.
“What we do have in place now is an independent athlete integrity unit, we have independent sanctioning and discipline and we will be able to be a lot tougher and speed up the process.”
Russia was barred from international athletics after last year’s McLaren report claimed more than 1,000 athletes benefited from a state-sponsored doping programme between 2011 and 2015.
Coe said in April he was “disappointed” by the lack of progress made by Russia in anti-doping reforms.
What about Eugene being awarded 2021 Worlds?
Coe was also asked about Eugene, Oregon being awarded the 2021 World Athletics Championships.
The decision is being investigated by the FBI and the Criminal Division of America’s Internal Revenue Service (IRS), the BBC learned.
The US city was awarded the event in 2015 with the IAAF bypassing the usual formal bidding process.
“First of all, 23 people voted for Eugene, Oregon,” said Coe.
“Every sport wants to get into the United States. It has been a very clear intent from the IAAF to have a World Championships in the United States.
“I would have loved other cities in the United States to have bid for it. Eugene wasn’t our choice, it was the choice of United States Track and Field Association.
“Eugene and Qatar came within three votes of each other and the council made a judgment that we needed to have a presence in the United States.
“If anything subsequently comes out of that that gives us any reason for concern we will look at that.”