The league announced the suspensions on Friday.
McBean and Williams are suspended for Denver's first six games of the 2012 season. Green is suspended for the team's first four games. All three are suspended without pay.
The players are eligible to participate in all offseason and preseason practices and games.
Williams issued a written statement calling his suspension unjust and vowing legal action. Green tweeted that he has now been approved for the medication for which he has been banned.
Williams said in his written statement that the NFL contends the urine sample he provided to an NFL specimen collector for testing wasn't from a human.
"We proved - conclusively - at the NFL hearing on this matter that the NFL and its specimen collector wholly failed in their duties to safeguard and process my specimen properly," Williams said. "In fact, the specimen collector was fired by the NFL after compromising my specimen as well as others.' The hearing officer, an NFL executive, ignored the NFL's own policy, engaged in inappropriate communications with top NFL officials about this matter without my knowledge or approval, corrupted the system, ignored that my specimen had been compromised, and now has subjected me to humiliation as well as suspension."
Williams' lawyer Peter R. Ginsberg said the specimen collector, whose name he wouldn't disclose, has said he watched Williams void directly into the specimen bottle, so it would've been impossible for the specimen to be non-human.
"This can only be explained by delving into the activities of the specimen collector. The NFL ignored that aspect," Ginsberg said in a telephone interview.
When asked whether Williams is denying tampering with his urine sample, Ginsberg said: "Our lawsuit will speak for itself, but D.J. is outright denying there is any justification for the suspensions. He's never tested positive for anything. He's been in the NFL for eight years. The NFL has chosen to do something that compromises his reputation based on clear violations of procedures and safeguards that are supposed to protect against this very thing. D.J. has never used steroids and there is simply no validity to the NFL's testing procedures."
Added Williams in his written statement: "I am proud of my record and proud of the way in which I conduct myself as a professional athlete and citizen."
Green tweeted: "I was suspended for taking ADHD medication prior to approval from NFL. I have now been approved to take the medication to treat my ADHD.
"I apologize to my teammates, the Bronco Organization and my family and friends. Thank you guys for all your support," Green added.