Anthony Joshua brushed off Jarrell Miller's taunts after the pair came face-to-face in London to promote their world heavyweight title fight.
IBF, WBA and WBO champion Joshua will fight in the United States for the first time as a professional in New York on June 1.
That bout will also represent the first for a world title for Miller, who in 2014 was given a nine-month suspension by the California State Athletic Commission for the banned stimulant methylhexaneamine.
The 30-year-old said he had noticed a change in Joshua's physique, although added that he believes the Briton will be clean when the pair meet at Madison Square Garden.
Joshua, who has never failed or rejected a drugs test, responded: "He's looking at my change between 2012 and 2013 but why doesn't he look at the 11 years?
"Around the Olympics I was around 104kgs, then when I turned pro I was around 107kgs, so that's around half-a-stone. I am 115kgs, so that's 11kgs in 11 years; it averages out. It's just my dedication.
"It's not the first time this has happened. So many fighters will be accused but I get tested and if, in the next 10 years, something was to come up then it would be a genuine mistake because I do not shove needles up my a***."
Miller revealed that both fighters have agreed to between 10 and 12 weeks of drug testing in the build-up to the bout.
Joshua confirmed: "I am on (drug testing scheme) ADAMS whereabouts, they have to know where I am for an hour every day and could walk in anytime.
"They can turn up any time during the day and that is a lifetime commitment. I have been on that since 2012 and I pay £40,000-a-fight to be tested by VADA two times a week.
"Jarrell Miller has been banned for drugs, so maybe that's why he's saying it."