The announcement came via a statement from general manager Kevin Colbert and noted that Gilbert will not appeal the ruling and will not be eligible to return until after the team's Dec. 17 game against the New England Patriots.
"We are disappointed that Marcus Gilbert has been suspended four games for using performance-enhancing substances," Colbert said. "The suspension is effective immediately, and he will not be permitted in the building until after the suspension has concluded following our game on Dec. 17."
Gilbert has started just five games for the Steelers this season because of hamstring issues after starting 13 in 2016 and all 16 in the 2015 campaign.
He is part of an offensive line Football Outsiders ranks as the 11th-best run-blocking unit and best pass-blocking unit in the league this year.
The suspension means the Steelers will have to fill the hole in their offensive front for contests against the Green Bay Packers, Cincinnati Bengals, Baltimore Ravens and Patriots as they battle for positioning in the AFC playoff picture down the stretch. His absence in the game against New England is particularly notable, since each team is battling for the No. 1 seed.
Pittsburgh will likely turn toward Chris Hubbard at right tackle while Gilbert is out.