"My personal thinking is that some of these murders have to do with drugs -- psychiatric drugs, street drugs," he said. "They've found a lot of common denominators are things like Prozac that are altering people's states of mind."
Preston, Travolta's wife, also came to Cruise's defense in 2005, when he was criticized for his public attack on Brooke Shields for using psychotropic medication to ease her postpartum depression.
Late Monday, in a statement to ABC News, the Church of Scientology responded to critics who claim it does not promote medical treatment.
"Scientologists seek conventional medical treatment for medical conditions," the church said in a statement. "Scientologists use prescription drugs when physically ill and also rely on the advice and treatment of medical doctors. The Church does not involve itself in the diagnosis or classification of any medical condition."
ABC News' Eileen Murphy, Lauren Cox and Kirk Fernandes contributed to this report.