Former world champion Tyson Gay and Jamaica’s ex-100m world record holder Asafa Powell have failed drug tests.

American Gay, 30, the joint-second fastest man ever over 100m, was told by the US Anti-Doping Agency on Friday that his A sample from an out-of-competition test in May was positive.

Powell, the all-time fourth quickest, tested positive for a banned stimulant at June’s Jamaican Championships.

UK Athletics performance director Neil Black said “Athletes must be sure they are looking at every aspect of what they do, what they take, when they take it, why they take it. Check, check, check, check, check.” He added, “When in doubt, don’t take it.”

For information on the safe use of supplements read The Athlete’s Guide to Sports Supplements