A person familiar with Jeremy Mayfield's drug test results says the positive finding was not for a performance-enhancing drug.

The person spoke to The Associated Press on Thursday on the condition of anonymity because NASCAR won't reveal what banned substance was found in the May 1 random test. Mayfield ultimately received an indefinite suspension.

NASCAR officials previously announced the drug violation was not alcohol-related. The administrator of its drug testing program dismissed Mayfield's explanation that he mixed a prescription with an over-the-counter medicine.

Under the sport's policy, that leaves the possibility that Mayfield tested positive for abuse of a prescription drug, narcotics or controlled substances, such as cocaine, marijuana or methamphetamine.