The seven-time Cy Young Award winner was interviewed by phone on ESPN Radio's "Mike & Mike in the Morning." He said he chose to speak out Tuesday because it was the official release date of a book about his alleged drug use, "American Icon: The Fall of Roger Clemens and the Rise of Steroids in America's Pastime" by four New York Daily News reporters.
Clemens said he had given a DNA sample to federal investigators but that syringes provided by McNamee would not link him to performance-enhancing drug use.
"It's impossible because he's never given me any," Clemens said.
Clemens is under investigation by a federal grand jury in Washington that is trying to determine whether he lied when he told a congressional committee last year that he had not used illegal performance-enhancing drugs. Clemens said he had not testified before the grand jury.
He also has sued McNamee, who told baseball investigator George Mitchell that he had injected Clemens with drugs.
Clemens said Tuesday it would have been "suicidal" for him to use steroids because of a history of heart problems in his family. He also repeated his much-lampooned use of the word "misremembers" about friend and former teammate Andy Pettitte's statement that Clemens told him he used HGH.
Clemens said he has spoken to Pettitte a few times, but not about the drug allegations.
"Everywhere I've gone and gotten the opportunity to speak to young kids or college kids, I take a lot of pride in telling those boys to get after it and do things the right way and take care of your body, because I know how I did it; I know how hard I worked," Clemens said. "For some of that to come in question, of course it's hurtful. But it's not going to break my spirit."