The NFL does not release details of drug violations. Smith, a five-time Pro Bowler and the leading receiver in franchise history, issued a statement through the team.
"I would like to apologize to my families, friends, the Jaguars organization and fans," Smith said. "I would especially like to apologize to (Jaguars owner) Wayne Weaver, who I know I have embarrassed and disappointed so much. I am sincerely sorry that I have concealed this from everyone and let them down."
Smith, 34, will be allowed to play the remainder of the preseason, but must sit out the first four regular-season games. He will not be eligible to rejoin the team until Sept. 29.
In 2001, he was pulled over on suspicion of drunk driving and was found to have cocaine in his system. The charges later were dropped. He has seven straight 1,000-yard receiving seasons.