CHARLOTTE, N.C. -- AJ Allmendinger tested positive for prescription Adderall, the suspended NASCAR driver told ESPN in an exclusive interview Tuesday.

Adderall is typically prescribed for attention deficit hyperactivity disorder, Allmendinger said. He does not have ADHD and therefore had no prescription.

He explained that he had been out in Louisville, Ky., the Wednesday before the Quaker State 400 race at Kentucky Speedway and was tired.

A friend of a friend, Allmendinger said, handed him a pill and stated it was a workout supplement that would give him energy. Allmendinger ingested the pill. Two days later he was randomly tested at the racetrack, a test he would ultimately fail.

He said neither NASCAR nor its drug testing team from Nashville-based Aegis Labs informed him of the specific substance in question until after a B sample was tested July 24, only that he had tested positive for an amphetamine. It was not until he was informed it was Adderall that he traced it back to that night in Kentucky.

Allmendinger said he does not abuse Adderall, rather that he took it just once.