World and Olympic 100m champion Justin Gatlin has been banned for up to eight years after accepting he committed a doping violation.
Gatlin has been banned after failing a drugs test in April
The United States Anti-Doping Agency (Usada) has set the maximum suspension, but the actual length of it will be determined by an arbitration panel.
Gatlin, 24, was facing a life ban after testing positive for testosterone, his second doping offence, on 22 April.
But he has agreed to "co-operate in the effort to eradicate drugs from sport".
The ban came into effect on 15 August, and is set to run until 24 July, 2014, unless it is overturned or reduced at the arbitration hearing.
We're shooting for (a ban of) way less than two years
Justin Gatlin's lawyer
But Gatlin will forfeit results from 22 April, the date of his positive test, including the 100m world record he ran in Doha in May of 9.77 seconds, a time he jointly holds with Jamaican Asafa Powell.
Despite his youth, an eight-year suspension would effectively end his career, but Gatlin's legal team are optimistic they can avoid a harsh punishment.
"We're shooting for something way less than two years," said Gatlin's lawyer Cameron Myler. "The goal is to have him back on the track as soon as possible."
And fellow Gatlin lawyer John Collins said the sprinter would plead "exceptional circumstances".
"The last time I represented Justin, the (arbitration) panel specifically found that he neither cheated nor intended to cheat, and I expect when all the facts and circumstances in this case come out, there will be a similar finding," Collins said.
Gatlin first failed a drugs test in 2001 when amphetamines were found in his samples at the USA Junior Championships.
But it was accepted that medicine he had been taking for 10 years to control attention-deficit disorder was the reason for the failed test.
He's acknowledging the accuracy of the positive test
Usada general counsel Travis Tygart
Gatlin was suspended for two years, but the world governing body the IAAF reinstated him after one year.
Under the World Anti-Doping Agency (Wada) code, a second positive test should constitute a lifetime ban unless the athlete can produce a compelling reason to have it reduced.
Usada's chief executive officer Terry Madden said the circumstances of Gatlin's first offence put his violation in a unique category.
"Given these circumstances and consistent with the international CAS (Court of Arbitration for Sport) precedent, a maximum of an eight-year suspension is a fair and just outcome," Madden said.
In accepting he committed a doping offence, if Gatlin appeals in the next six months to have his penalty reduced, he will not be able to argue that the test was faulty.
"To his credit, it's recognition that the science is reliable," said Travis Tygart, general counsel of Usada.
"Instead of wasting a bunch of resources attempting to create smoke where there's not any, he's acknowledging the accuracy of the positive test.
"In exchange for his agreement to co-operate, we've recognised the nature of his first offence."
While we are glad Justin has taken responsibility...we are sorely disappointed in him
USA Track & Field CEO Craig Masback
"He accepted liability," added Tygart. "He agreed not to raise technical arguments or frivolous defences.
"He has an opportunity to go to a panel of arbitrators and argue exceptional circumstances."
If the IAAF does not approve of the ban ultimately handed to Gatlin by Usada, it can appeal to the Court of Arbitration for Sport for a longer suspension to be imposed.
Coach Trevor Graham has contended Gatlin tested positive after a massage therapist used testosterone cream on him without his knowledge.
But Gatlin is now at least the seventh athlete trained by Graham, who is under investigation by the IAAF and Usada, to be charged with a doping offence.
USA Track & Field chief executive officer Craig Masback said: "Gatlin's doping case has been a setback for our sport.
"While we are glad Justin has taken responsibility for his positive test and will co-operate in Usada's anti-doping efforts, we are sorely disappointed in him."
Powell said it was "a good thing" Gatlin had co-operated with the anti-doping authorities.
He added that he had considered himself to be the sole holder of the world record from the moment news of Gatlin's positive test came out.