Reigning 100 metre Olympic champion Justin Gatlin went undercover and wore a wire in order to have an eight year ban for doping reduced to four.
The United States Anti-Doping Agency (USADA) has confirmed that Gatlin was informed on Monday of the decision handed down by three US arbitrators.
Gatlin tested positive for testosterone on April 22nd, 2006 - his second positive doping test - and has spent the past 20 months fighting the charge.
The 25-year-old faced a lifetime ban under World Anti-Doping Agency rules but was given an original eight-year suspension after agreeing to help the USADA with its investigation into doping in the sport.
A statement from the arbitrators published on the USADA website, www.usantidoping.org, said: "He \[Gatlin] made undercover calls. He wore a wire, putting himself at risk ... The record reflects extended assistance to the United States Government, which goes far beyond the contemplated assistance to anti-doping sports authorities."
Gatlin's ban is retroactive to May 25th, 2006 and runs until May 24, 2010, meaning he will be unable to defend his Olympic crown in Beijing later this year.
Two of the three arbitrators decided on a four-year ban because of a previous positive test. The usual penalty for a first offence is two years, while a second offence can result in a lifetime ban.
Gatlin first tested positive for a stimulant in 2001, during his first major US competition while in college at Tennessee.