American former 100m and 200m world champion Tyson Gay has been suspended for a year after testing positive for a banned anabolic steroid.

Gay, 31, has also returned the silver medal he won in the 4x100m relay at the London Olympics two years ago.

 His results since 15 July 2012, the date he first used a product containing a banned substance, have been annulled.

His suspension has been backdated to 23 June 2013, the date he tested positive at the US World Championship trials.

That was one of three tests Gay failed, with two taken out of competition.

Gay, the joint-second fastest man ever over 100m, is eligible to return next month and can compete in future Olympics and World Championships.

He could have been banned for up to two years but received a lighter penalty as he co-operated with the US Anti-Doping Agency (Usada).

"We appreciate Tyson doing the right thing by immediately withdrawing from competition once he was notified, accepting responsibility for his decisions, and fully and truthfully co-operating with us," said Usada chief executive Travis Tygart.

Gay immediately expressed regret after his positive test at last year's US World Championship trials.

He said: "I don't have a sabotage story... I basically put my trust in someone and was let down.

"I hope I am able to run again, but I will take whatever punishment I get like a man."

Gay won gold in the 100m, 200m and 4x100m at the 2007 World Championships.