In a television interview, AJ Allmendinger has revealed that a prescription drug called Adderall used to treat attention deficit hyperactivity disorder was to blame for his failed drugs test, which has resulted him being placed on indefinite suspension from NASCAR competition until he completes a 'road to recovery' rehabilitation program.

Talking to US sports network ESPN in an exclusive interview on Tuesday, Allmendinger said that a friend of a friend had handed him a pill on a night out, calling it a workout supplement, when he had complained of feeling tired. He said it was because he had not been sleeping well in the week before May's Quaker State 400 Sprint Cup race at Kentucky Speedway, where he ended up being selected at random for a drugs test.

"I was really tired, had no energy, nothing," Allmendinger also told "One of [my friend's] friends said, 'Oh, I have an energy pill that I take for working out.'

"I didn't think anything of it because I've taken energy supplements for working out that my trainer gives me," he added. "I didn't even think about it. That was my big mistake."

Allmendinger said that it had been a one-off situation and that he had not taken Adderall previously or since. He does not have ADHT and has no prescription for medication to treat the condition.

Previously, Allmendinger had said that he would be having all his various foods and workout supplements checked for the source of the positive drugs finding. He said that it was only after he had accepted the results of the 'B' sample test and that he was informed that the stimulant in question was Adderall that he was able to piece together what must have happened.

NASCAR spokesman David Higdon earlier appeared to cast some doubt on this, however, saying that the sanctioning body itself did not know the specific substance that had caused Allmendinger's test result. Moreover, previous information from NASCAR had suggested that the drugs test used was not sensitive enough to identify a specific substance down to brand level, especially not once the substance had metabolised in the body.

Allmendinger says that the 'road to recovery' program is treating his case as more stress management than drugs rehabilitation, and that he hoped that he would complete the process by the end of August and be eligible for reinstatement soon afterwards.

Allmendinger's recollection of the circumstances in which he came to take the substance will not change the need for him to undergo NASCAR's mandatory bespoke rehabilitation program. Nor will it change his position with his former team, Penske Racing, which last week confirmed that it had dismissed the 30-year-old Californian.

Allmendinger's friend and business partner Michael Shank has indicated that he would like the driver to come and spearhead their joint new MSR Indy venture in the IZOD IndyCar Series in 2013 if no openings were available in NASCAR.

Adderall has an unfortunate association in NASCAR with the case of Jeremy Mayfield, the only other Sprint Cup driver to be suspended for substance abuse. Mayfield claimed that his own positive drugs test in 2009 was caused by a combination of Adderall - for which he had a prescription to treat his ADHT condition - and an over-the-counter allergy medication, Claritin D.