Mike Tyson and Roy Jones Jr have both returned negative results for drug tests administered on fight night from last month's exhibition.
Tyson, 54, came out of retirement to face Jones Jr, 51, in an eight-round bout in Los Angeles, California.
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The blockbuster match-up at the Staples Centre ended in a draw.
The pair of boxing legends had to pass pre-fight drug tests with the Voluntary Anti-Doping Association (VADA) ahead of their fight.
Tyson and Jones Jr completed a drug-testing program administered by VADA before their exhibition.
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And they also passed their fight night doping tests with both men's samples clear.
That's despite Tyson smoking cannabis on the day of the fight, but VADA do not test for cannabinoids
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California is one of many states in the US that has legalised the use of marijuana both medicinally and recreationally.
Speaking after his ring return, he admitted: "Listen, I can't stop smoking.
"I smoked during fights. I just have to smoke. I'm sorry. I'm a smoker."
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'Iron' Mike earned a reported £7.5 million while 'Captain Hook' is thought to have earned around £2.5 million.
Tyson appears set to continue his boxing comeback with former foes Buster Douglas and Evander Holyfield calling him out.
He lost to both Douglas and Holyfield during his professional career.
Featured Image Credit: PA/TrillerTopics: Mike Tyson, Boxing News, Roy Jones Jr, Boxing, Fight News