The Olympic silver medallist Nick Willis says there was a point in his career when he considered giving up athletics because of doping cheats.
There have been reports that a third of endurance medalists blood tests at World Championships and Olympic Games between the years 2001 and 2012 were suspect, including 55 gold medal winners.
Willis finished third in the 1500 metres at the Beijing Olympics but was promoted to second after the winner Rashid Ramsi of Bahrain was disqualified for doping.
Willis says early on his professional career he realised what he was up against, when the two of the three 1500m medallists at the 2005 world champs in Helsinki tested positive for doping.
"I suspect many others in that race were probably also doping as well," he said.
"I had just missed out on the final by a fraction of a second and had to watch the final from the stands which is never a fun experience. That was actually my very first summer as a professional and I was a young 22-year-old and I questioned 'is it really worth it?'"
"I went out and bought a skateboard and went skating around the streets of Helsinki. I had a really bad slam smashing my back against a wall and that woke me up. I realised this is a privilege, you have a unique opportunity and the world is like this and you've got to be an example to fight through this," he said.
Willis believes over the past five years the level of doping has reduced.
"I actually do believe it has got better (a reduction in doping)... and this report actually says that.
"If you look at the data it has significantly reduced since 2009, only 70 out of the 700 suspicious tests actually came through in that timeframe."
He puts the decline in "blatant cheating" down to the introduction of the blood passport in 2009, which profiles biological markers and helps detect doping.
"Many are still finding ways to skirt around the system... what they are having to do now allegedly is micro dosing, where they take smaller doses more frequently as opposed to these large, preferable amounts."
Willis is currently in altitude training in Flagstaff, Arizona in preparation for the world champs in Beijing later this month.
It will be the first time he has returned to compete at the Birds Nest stadium in Beijing since his Olympic success there seven years ago.