Belfast boxer Brian Magee says he has emerged from "six months of hell" after his positive drugs test was made public on Monday.
Magee is in the final weeks of a six-month ban after testing positive for the prohibited stimulant oxilofrine.
The 38-year-old failed the test after his WBA super-middleweight title defeat by Mikkel Kessler in December.
The UK Anti-Doping Agency ruled Magee had not deliberately sought to enhance his performance.
Magee escaped a two-year suspension by showing the substance had been an unlabelled ingredient in an 'over the counter' sports drink.
"I got the news about three weeks after the Kessler fight," Magee told BBC Sport Northern Ireland.
"It was a total shock. After the disappointment of getting beaten in the fight, for this to come out after my 25 years in boxing was terrible. I was just devastated."
Magee initially feared for his boxing career.
"But my manager Pat Magee and the team around got working straight away to try to work out what had happened because I knew that I hadn't intentionally taken any banned substance," he added.
"I gave the UK Anti-Doping Agency everything I had ever taken and everything was fine in terms of those ingredients.
"Pat then decided to get everything independently tested.
"It worked out that the product had been contaminated in the factory where it was made.
"We went to the shop where I got it and bought more and, after testing the second batch, found that it was also contaminated."
Jamaican sprinters Asafa Powell and Sherone Simpson tested positive for the same stimulant following their national trials last month.
Magee acknowledged some people will be sceptical about his version of events.
He said: "I would be a total advocate of a zero-tolerance policy when it comes to drugs in sport.
"I've been tested 40 times throughout my career and maybe 20 times in the UK.
"I've always applied all the correct protocols because I knew there was nothing out of the ordinary that I've ever done."
Magee had been mulling over his future after his third-round stoppage by Kessler but is now determined to fight again.
He said: "I'm back training over the last two weeks and with the ban elapsing later this month, fingers crossed I'll be back in the ring before the end of this year.
"I owe everyone who has supported me to have one (bout) for the road."