A therapeutic amount of the drug Luvox was found in Eric Harris' system after he died, the Jefferson County coroner's office has said.
Solvay Pharmaceuticals Inc. makes the drug to treat obsessive-compulsive disorder and depression. The lawsuit filed Friday in U.S. District Court claims Solvay failed to warn Harris' doctor about side effects.
"Such drugs caused Eric Harris to become manic and psychotic," the lawsuit states.
Solvay's Web site warns that the drug may impair judgment, thinking or motor skills.
The American Psychiatric Association defended Luvox in 1999, saying a decade of research found little relationship between the use of antidepressants and destructive behavior.
Harris and Dylan Klebold killed 12 students and a teacher and wounded 26 people before taking their own lives on April 20, 1999.
The plaintiffs are seeking damages in excess of $75,000 each.
Victims' families have also filed lawsuits against the sheriff's department, school officials and three men who worked at a gun show where the gunmen got some of their weapons.
Some families have reached settlements with the gunmen's parents and people who helped provide the weapons.
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