The NFL has suspended Colts guard Jaimie Thomas for four games for violating the substance policy.
Thomas, who currently is on injured reserve, violated the anabolic steroids and related substances policy.
The league and the Colts did not say what prohibited substance he tested positive for.
Thomas was a seventh-round selection by the Colts in the 2009 draft and played in eight games with Indianapolis in 2010.
He was placed on IR on Aug. 19 this year with a back injury.