Gay, the 30-year-old American who was world champion in 2007 and the fastest man in the world this year, tested positive for a banned substance and immediately withdrew from next month's world championships in Moscow.
Jamaican sprint star Powell, a former 100m world record holder, confirmed that he had tested positive for a banned stimulant at his country's national trials for Moscow.
But the 30-year-old strenuously denied any wrong doing.
Only Olympic champion and world record holder Usain Bolt (9.58sec) has gone faster than Gay, whose best of 9.69sec he shares with Yohan Blake of Jamaica. Powell is the fourth fastest man of all time with 9.72sec.
Gay was informed by the United States Anti-Doping Agency (USADA) on Friday of his failed test and on Sunday the USA Track & Field (USATF) said he had pulled out of the world championships.
"He stated he is withdrawing," said USATF spokesperson Jill Geer.
USADA said Sunday that the 30-year-old's B sample has yet to be tested so they would not confirm or deny the failed test.
"In response to Mr. Gay's statements, USADA appreciates his approach to handling this situation and his choice to voluntarily remove himself from competition while the full facts surrounding his test are evaluated," USADA media relations manager Annie Skinner told AFP.
"The B sample will be processed shortly, and as in all cases all athletes are innocent unless or until proven otherwise through the established legal process, and any attempt to sensationalize or speculate is a disservice to due process, fair play, and to those who love clean sport."
Gay told US media he had made a mistake and been let down by someone else.
USATF said they would continue to look towards USADA to help them weed out drug cheats in the sport.
"USA Track & Field is strongly opposed to doping, and we respect the work that USADA has done as a leading agency globally in the fight against drugs in sport," USATF chief executive Max Siegel said.
Gay had run the fastest time in the world this year at June's US trials for the world championships in Iowa. His 9.75sec was the 10th fastest 100m of all time.
World record holder Bolt's best time over 100m this season is 9.94sec set in Kingston in June.
Gay won the triple of 100m, 200m and 4x100m relay in Osaka at the 2007 world championships while also claiming a 4x100m silver medal at the London Olympics last year.
Powell, also 30, took to Twitter to confirm his dope test failure.
"I will confirm that a sample I gave at the National Trials in June has returned 'adverse findings'," he said.
"The substance oxilofrine was found, which is considered by the authorities to be a banned stimulant.
"I want to be clear that I have never knowingly or wilfully taken any supplements or substances that break any rules. I am not now nor have I ever been a cheat."
Powell held the 100m world record between June 2005 and May 2008.
He won two bronze medals in the 100 metres at the 2007 and 2009 world championships. He also had one gold in the 4x100 metre relay in 2009.
But he has never managed an individual sprint medal at the Olympics, finishing fifth in the 2004 Athens and 2008 Beijing Olympic 100 metre finals and limping home in eighth place in the final in London last summer.
According to media reports, Powell was one of five athletes who failed drug tests at the national trials last month in Kingston.
Sherone Simpson, a silver medallist in the women's 100m at the 2008 Olympics, was one of them, according to a report in Britain's Daily Telegraph.
The Jamaica Gleaner newspaper claimed the substance taken may have been contained in a food supplement.
"My team and I will try to do everything we can to get this issue dealt with as best as we can," Simpson told the Gleaner.
"Thanks to all who have been supporting me, I really appreciate it at this time."
Later Sunday, Powell's agent, Tara Playfair-Scott, revealed on Twitter that a man who allegedly supplied the supplements had been arrested in Italy.
"He has been detained by Italian Law Enforcement in conjunction with this matter. The investigations continue," she wrote.