* Gay banned for one year, returns Olympic medal
* Results from 2012 all erased from record books
* Allowed to return to competition in June
Gay has also returned the silver medal he won with the U.S. 4x100 metres relay team at the 2012 London Olympics but will be eligible to return to competition as early as next month after admitting his offence and co-operating with investigators.
"We are thankful he decided to come in and be truthful in his cooperation with us," USADA chief executive Travis Tygart told Reuters.
"With the loss of results since 2012, including an Olympic medal, he has suffered serious consequences, but by cooperating he has tried to help the sport move forward for the good of clean athletes."
As part of the suspension he accepted, Gay, the joint second fastest man in history, was disqualified from all competitive results since July 15, 2012, the date he first used a product that contained a prohibited steroid.
The start of his ban was backdated to June 23, 2013, the day his doping sample was collected at the USA Outdoor Track & Field Championships and when he voluntarily stopped competing after being notified of his positive test.
The American 100 metres record holder can return to competition next month and will be eligible under U.S. rules for future world championships and Olympics.
He had tearfully admitted last July he had failed an out-of-competition doping test, saying "I basically put my trust in someone and I was let down."
"I don't have a sabotage story. I don't have lies," Gay, who had previously spoken out against doping, said in a 2013 interview, adding he had never knowingly taken a performance-enhancing drug. "I made a mistake."
The 31-year-old could have been suspended for two years for his first doping offence but received a reduction because of his substantial assistance into the investigation of his case, USADA said.
An investigation into the circumstances of his case is ongoing and could produce additional suspensions, track and field sources said.
The ban is also subject to appeal by the International Association of Athletics Federation and the World Anti-Doping Agency.
The United States Olympic Committee (USOC) confirmed it had received the medal Gay won at the London Olympics and would be forwarding it to the International Olympic Committee (IOC).
"We were extremely disappointed to learn that Tyson Gay committed a doping offense," USOC spokesman USOC spokesman Patrick Sandusky said in an email.
"The USOC remains committed to the fight against doping and will continue to invest substantial resources to ensure that the United States is and remains a world leader in anti-doping efforts."
The IOC will determine whether other members of the U.S. relay team will be allowed to keep their medals. The committee has offered varying opinions in past cases.
USA Track and Field also expressed disappointment that one of its biggest names had tested positive.
"USA Track & Field is gravely disappointed any time an athlete uses performance-enhancing drugs, and Tyson Gay's case serves as a lesson about the consequences of making poor decisions," USATF chief executive Max Siegel said in a statement.
"We appreciate that Tyson accepted responsibility and has assisted USADA by providing information to help battle the use of PEDs. We thank USADA for their vigilant work on this case and for their leadership in the pursuit of clean sport.
A spokesman for Gay said his client was unlikely to make any public comments on the case for several days.
Gay's suspension follows hot on the heels of another ban to a big-name sprinter.
Jamaican former world record holder Asafa Powell was slapped with an 18 month suspension by Jamaican officials in April after a positive test for the banned stimulant oxilophrine. He is appealing the ban.
Only Jamaican world record holder Usain Bolt has a faster 100 metres time than Gay, whose 2009 clocking of 9.69 seconds was later equalled by Jamaican Olympic silver medallist Yohan Blake in 2012.
Soft-spoken and humble, Gay had seemed destined in 2007 to becoming the world's great sprinters, winning gold medals in the 100 and 200 metres and 4x100 metres relay at the Osaka world championships.
But injuries and the emergence of Bolt shattered those dreams as the lanky Jamaican dashed to world records and Olympic gold at the 2008 Beijing Games.
Bolt later lower both records to 9.58 seconds for the 100 and 19.19 for the longer sprint and repeated as the Olympic gold medallist in London in 2012.
Gay appeared ready for another run at Bolt at the 2013 world championships with eye-catching times at the U.S. trials.
But his admission to the failed doping test ended that opportunity as Gay withdrew from the championships and ended his 2013 season.