Davis said he has been taking the same supplements for the last seven or eight years and never had an issue.
On Friday, he issued an apology to fans via Twitter.
This is by far one of the saddest days of my NFL career. I never thought that this would happen to me. I’ve worked extremely hard to do things the right way on and off the field. Panther Nation please know that I am not a cheater. #KeepPounding pic.twitter.com/zUppMfm6yk— Thomas Davis (@ThomasDavisSDTM) April 6, 2018
Davis, 35, acknowledged he tested positive for an estrogen blocker but said "in no way would I ever do anything to cheat this game."
Davis, a former Walter Payton Man of the Year award winner, said he has a clear conscience about the situation knowing he didn't do anything intentionally wrong.
He plans to serve the suspension in what he previously said would be his 14th and final season with Carolina before retiring.
Davis started 15 games last season for the Panthers.
The Associated Press contributed to this report.