Mike Tyson and Roy Jones Jr both passed their fight-night doping tests ahead of their exhibition bout.
The two ring legends fought to a boring draw over eight two-minute rounds in Los Angeles last month.
Both men had enrolled with the Voluntary Anti-Doping Association (VADA) and both men's samples were clear.
VADA do not test for cannabinoids, however, and Tyson has since admitted smoking cannabis on the day of the fight.
"Listen, I can’t stop smoking," the former undisputed heavyweight world champion said.
“I smoked during fights. I just have to smoke. I’m sorry. I’m a smoker.
"I smoke every day. I never stopped smoking."
Tyson looked to have done enough to beat Jones Jr but the three judges were split as to the winner.
Three former world champions scored the bout with Christy Martin giving Tyson the nod 79-73,Vinny Pazienza opted for Jones by a score of 80-76 while Chad Dawson scored it level at 76-76.
Tyson, who retired as a professional in 2005 after losing to Kevin McBride, insists he will continue fighting next year.
"My body feels splendid - I want to beat it up some more," he said.
"Maybe (next) we do something in the south of France - Monaco or San Tropez and we do something out there with one of the European fighters.
"Anything is possible; the sky's the limit. I believe we broke all the records on pay-per-view concerning boxing. I just want to continue doing this from a humanitarian perspective."
Tyson and Jones Jr raked in millions from the fight after it was a surprise hit with fans in America.
As many as 1.6million people paid $50 to watch the two ageing legends, meaning Tyson could pocket $10m and Jones Jr $3m.
