American judo fighter Nick Delpopolo was expelled from the Olympic Games on Monday after testing positive for marijuana he said he ate accidentally before arriving in London.
Delpopolo is the first of the 10,500 games athletes to fail an in-competition doping test.
His case is the fifth positive test for a banned substance reported by the IOC since its official London Games testing period began in mid-July. The other four athletes were caught before competing.
The International Olympic Committee said it disqualified Delpopolo from the men's 73-kilogram class, where he placed seventh.
Delpopolo tested positive for metabolites of cannabis after competing on July 30.
He apologised to the United States team in a statement acknowledging he was "embarrassed by this mistake."
"My positive test was caused by my inadvertent consumption of food that I did not realise had been baked with marijuana, before I left for the Olympic Games," Delpopolo said in a statement released by the US Olympic Committee.
"I look forward to representing my country in the future, and will rededicate myself to being the best judo athlete that I can be," he said.
Delpopolo "shall have his Olympic identity and accreditation card cancelled and withdrawn immediately," the IOC said.
The IOC said it would ask the International Judo Federation to alter the standings in Delpopolo's event. He beat opponents from Hong Kong and Belgium, then lost to fighters from South Korea and Mongolia.
Delpopolo faces further sanctions as the IOC requested that judo's governing body "consider any further action within its own competence."