The 39-year-old, whose ban is effective immediately, said in a statement issued through the Major League Baseball Players Association today that he took a banned substance while re-applying for a Therapeutic Use Exemption due to a medical condition.
"I apologise to my team-mates, the Royals organisation and to the Kansas City fans," Tejada said in the statement.
"I have a medical condition that requires medication to treat. I took that medication while re-applying for a Therapeutic Use Exemption. Under the requirements of the Joint Drug Program, I made a mistake in doing so."
Tejada is currently on the 60-day disabled list with the Royals due to a calf strain. He joined Kansas as a free agent in the off-season and has struck three home runs and 20 RBIs in 53 games for the team.