Mellouli, who tested positive for amphetamines at a meet in Indiana on Nov. 30, 2006, was suspended by the Court of Arbitration for Sport after an appeal for a 2-year ban was filed by swimming's world governing body.

The ban, which dates back to the time of the doping offense, leaves Mellouli eligible to compete at next year's Beijing Olympics.

Mellouli won gold in the 800-meter freestyle and silver in the 400 freestyle in March at the world championships in Melbourne, Australia. He was the first Tunisian to win a gold medal at a world championships.

CAS ruled that those medals and all of Mellouli's results back to Nov. 30, 2006, are annulled.

CAS decided against the 2-year ban because Mellouli, who was studying at Southern California at the time of the positive test, admitted he took the substance.

"The swimmer admitted that he had taken an Adderall pill two days earlier to prevent him from falling asleep so that he could finish writing a report which counted towards his final university diploma," CAS said.

FINA filed the appeal with CAS after the Disciplinary Commission of the Tunisian Swimming Federation concluded that Mellouli had not taken the substance with the intention of enhancing his performance and sanctioned him with only a reprimand and a warning.

CAS noted that Mellouli did not ask for an analysis of the "B" sample.

"If the swimmer was indeed guilty of negligence, such negligence was not sufficiently serious to suspend him for two years, which would have meant an automatic ban from the 2008 Olympic Games in Beijing," the CAS panel ruled.