"This morning the NFL notified the team of Donald Stephenson's four-game suspension," the Chiefs said in a statement. "Obviously losing Donald is disappointing, but we are in full compliance with the league's policy. We will have no further comment on the situation."
Stephenson has played in all 32 games for the Chiefs since the team selected him in the third round of the 2012 NFL Draft. The Oklahoma product has started 14 games for Kansas City.
"I'm extremely sorry that I failed to check with the NFL, NFLPA, or Chiefs medical team before I took a medication that requires a therapeutic use exemption," Stephenson said in a statement released by the NFL Players Association.
"The rules are strict, and without a TUE, the consequence is a four game suspension. I apologize to the Hunt family, John Dorsey, Coach Reid and his staff, my teammates, and our awesome Chiefs fans. It is not a mistake I will ever make again. I will train extremely hard during my time away from the team, and I will be ready to contribute to my teams effort to win a Super Bowl as soon as I return."
Stephenson will be eligible to return to the Chiefs' active roster on Sept. 30 following the team's Sept. 29 game against the New England Patriots. He is eligible to participate in all offseason and preseason practices and games.