The toxicology report, filed by Westchester County District Attorney Janet DiFiore, disputes Kennedy's claim that a seizure caused her to crash her Lexus into a a tractor-trailer on Interstate 684 on July 13, the New York Post reported.
Kennedy initially told police she may have accidentally taken an Ambien instead of her daily thyroid medication.
"Moments after the accident occurred, I told police that it was possible that I may have inadvertently taken a sleep aid instead of my daily thyroid medication," Kennedy said in a statement Wednesday. "The results we received today from the Westchester County lab showed trace amounts of a sleep aid in my system, so it now appears that my first instinct was correct."
Last week, Kennedy, daughter of the late Sen. Robert F. Kennedy, denied that Ambien was involved in the crash, the New York Daily News reported.
"My doctors believe that this was caused not by a sleeping aid, but by a complex partial seizure," Kennedy said in North Castle town court. "My doctor says this is the first seizure I have ever had."
Kennedy was charged with driving while her ability was impaired by drugs. She has pleaded not guilty to the misdemeanor charges.