Major League Soccer has handed 10-match bans to New York Red Bulls players Jeff Parke and Jon Conway after they failed drugs tests, the first such cases in the U.S. league.
Both players tested positive for the performance-enhancing androstatriendione and boldenone metabolites and will miss their team's playoffs push.
MLS officials said the players bought supplements over the counter in a vitamins shop and were unaware they contained banned substances.
"We have met with both players and they informed us that they ingested an over-the-counter supplement that unknowingly contained a banned substance," Erik Stover, Red Bulls managing director, said in a statement posted on the team's website.
"This is a sad day for our club and our fans. We are extremely disappointed that Jon and Jeff have tested positive."
Conway, a goalkeeper, was ever-present this season while central defender Parke had missed only one game.
Both are unavailable for Saturday's visit by the Columbus Crew, where the Red Bulls, who are fourth in the Eastern Conference, have a chance to secure a playoff berth.