The positive result from a July 6 random test was included in a U.S. District Court filing Wednesday that included an affidavit from Mayfield's stepmother, who claimed she personally witnessed the driver using methamphetamine at least 30 times over seven years.
Mayfield once again denied ever using the illegal drug.
"I don't trust anything NASCAR does, anything (program administrator) Dr. David Black does, never have, never will," Mayfield told The Associated Press.
Lisa Mayfield said she first saw the driver use meth in 1998 at a race shop in Mooresville, N.C. She said Mayfield cooked his own drugs until the ingredient pseudoephedrine was taken off the shelves and it became too difficult for Mayfield to obtain the ingredients. She said her stepson then began to purchase meth from others.
"Between 1998 and 2005, I am personally aware that Jeremy used methamphetamines often," she said in her affidavit. "I was concerned about his heavy use and talked to his father about it. I saw Jeremy use methamphetamine by snorting it up his nose at least 30 times during the seven years I was around him."
Mayfield angrily contested the account.
"She's tried everything she can do to get money out of me, I won't help her, so I guess she found a way to get money from NASCAR by giving them an affidavit full of lies," he said.
Mayfield was suspended May 9 for failing a random drug test conducted eight days earlier. NASCAR later said he tested positive for methamphetamine.
He sued, and U.S. District Court Judge Graham Mullen issued an injunction July 1 that allowed Mayfield to return. Mullen based his decision on Mayfield's argument that the testing system is flawed. He also gave NASCAR the right to test Mayfield at any time.
NASCAR did just that July 6 and said in its filings that the "A" sample had levels of methamphetamine consistent with habitual users who consume high doses.
On July 6, Mayfield also had a second test at a lab chosen by his attorneys. May-field attorney John Buric said that test came back negative but was sent back to the lab Wednesday for "reconfirmation."
Also Wednesday, the last remaining employee of Mayfield's race team, general manager Bobby Wooten, said he resigned because he doesn't believe Mayfield Motor-sports will return to the track.