Usain Bolt says drug cheats in athletics leave him "frustrated and angry".
The Jamaican sprinter is in London for the Anniversary Games, which begins at the Olympic Stadium tomorrow night.
Bolt is a month away from the World Championships in Beijing, where he will come up against 100 metres rival Justin Gatlin who has been banned for drug-taking twice.
"Throughout the years when you work hard and the sport's getting back a good reputation and then when other athletes decide they want to do the wrong thing. It definitely does upset me, because then everybody starts pointing fingers again and starts speculating. It doesn't help the sport in any way. At times I do get frustrated and angry," he said.
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