The suspension covers Minnesota's final three regular-season games and first playoff game. The NFL does not specify the substances for which players test positive.
A message was left seeking comment from Henderson's agent, Brian Mackler.
Henderson is the younger brother of fellow linebacker E.J. Henderson, who broke his left leg Dec. 6 and is out indefinitely.
The Vikings have had several run-ins with the league for alleged violations of its performance-enhancing drugs policy. In 2007, defensive end Ray Edwards was suspended for four games.
The NFL has been fighting for the right to impose four-game suspensions on Vikings defensive tackles Kevin Williams and Pat Williams. They tested positive in 2008 for the diuretic bumetanide, which the NFL prohibits because it can mask the presence of steroids. The Williamses, who are not related, ingested the banned drug when they took the weight-loss supplement StarCaps, which did not state on the label that it contained bumetanide.
The NFL has been unable to persuade the courts so far that federal labor law and the league's collective bargaining agreement should trump Minnesota state laws regarding drugs in the workplace. After losing its latest round in a federal appeals court on Monday, NFL spokesman Greg Aiello said the league was considering an appeal to the U.S. Supreme Court. The Williamses' suspensions remain on hold pending the outcome of their lawsuit in state court in Minnesota, which seeks to permanently block the suspensions and is set for trial March 8.
Copyright 2009 by The Associated Press