Herold tells The Associated Press that she "never, ever" gave the drug to her 14-year-old chimp Travis. The animal on Monday attacked Herold's friend, Charla Nash, 55, leaving her with critical injuries to her face and hands.
Police have said that Herold told them that she gave Travis Xanax earlier on Monday to calm him because he was agitated. In humans Xanax can cause memory loss, lack of coordination, reduced sex drive and other side effects.
A University of Chicago doctor says it can also lead to aggression in people who are unstable to begin with.
A call was placed with Stamford police seeking comment.