CHARLOTTE, N.C. — Jeremy Mayfield denied Thursday ever taking methamphetamines, doesn't know how he failed a random drug test and said his indefinite suspension from NASCAR has ruined his driving career.

Mayfield's denial comes in an affidavit that was among several hundred pages of documents filed by his attorneys in U.S. District Court. He's been suspended since May 9 for failing a random drug test conducted eight days earlier at Richmond International Raceway.

"I have never taken methamphetamines in my life, and when accused of taking them I immediately volunteered to give another urine sample," Mayfield said in the affidavit, which also says his offer of a second sample was denied.

NASCAR has refused to reveal what drug Mayfield was caught using, classifying it only as a "a dangerous, illegal, banned substance." Mayfield has said his positive test stemmed from the combined use of Adderall for Attention Deficit Hyperactivity Disorder and Claritin-D for allergies — an explanation that was rejected by Dr. David Black, CEO of Aegis Sciences Corp. in Nashville, Tenn., which runs NASCAR's testing program.

But Ohio forensic toxicologist Harry Plotnick disputed Black's dismissal in an affidavit in support of Mayfield, saying a component of Claritin in certain circumstances "could produce a false positive for methamphetamine."

Mayfield sued in late May to have his indefinite suspension lifted, and both sides were barred from discussing his test results. NASCAR is countersuing and alleges Mayfield breached his contract and defrauded NASCAR and its competitors of earnings. Both sides will be back in court July 1.

Mayfield indicated he'll try to qualify for next week's race at Daytona International Speedway if a federal judge reinstates him.

NASCAR also filed several documents Thursday, including affidavits from Jeff Gordon, Jimmie Johnson and Robby Gordon in which the drivers said they are not "willing to put my life at risk driving a race car on a NASCAR track with drivers testing positive for drugs that diminish their capacity to drive a race car."

NASCAR vice president of operations Steve O'Donnell said in an affidavit that permitting drug users to participate could cause serious injury or death to participants or fans.

"It would take a simple lapse of judgment by a driver under the influence of a banned substance to create a catastrophic accident," O'Donnell said.

Mayfield, who turned 40 last month, had been out of full-time work since his 2006 firing from Evernham Motorsports. He started his own race team this season, but his suspension covered both his roles — driver and owner of the No. 41 Toyota.

He transferred ownership to his wife, Shana, following his suspension, and she sent the team to two races with J.J. Yeley as the driver. Citing financial issues, she did not send the car to the last four races. The team is not listed on the entry blank for this weekend's event in New Hampshire.

In the court papers, Mayfield said the suspension caused his sponsor to stop funding the No. 41 Mayfield Motorsports entry, and he has been unable to find a company willing to work with his team. Mayfield said he's been forced to lay off 10 employees, and he and his wife have borrowed money from family and sold personal assets to meet their living expenses.

"I do not understand how or why this is happening to me or my family," he said in the affidavit. "I have always anticipated that I would be able to race for another ten years, but I believe my career will be effectively over if I am forced to sit out the rest of this season.

"I am afraid that I will have to sell my race team, and I know of no other way to make a living except as a professional race car driver."

His attorneys are contesting NASCAR's drug-testing procedure, and Mayfield said he never gave permission for his backup "B'' sample to be tested after his "A'' sample came back positive. He also said in his affidavit he was unaware of his right to have the "B'' sample tested by an independent laboratory.

His attorneys argue NASCAR's procedures are in violation of federal workplace guidelines because Aegis tested both the "A'' and "B'' samples. Thursday's filings include affidavits from several experts who challenge NASCAR's procedures, including sworn testimony from New Mexico laboratory quality auditor Janine Arvizu and Plotnick, who state that Aegis did not follow proper testing procedures.

The filing does not include testimony from Harvey MacFenerstein, an expert cited in Mayfield's May 29 filing. NASCAR last week filed a motion to have his testimony dismissed based on false credentials listed in his affidavit, and MacFenerstein told The Associated Press he told Mayfield's attorneys his qualifications had been exaggerated.

Mayfield attorney John Buric filed a 29-page response to NASCAR's motion Thursday, admitting he made two mistakes in his filing, including incorrectly qualifying MacFenerstein as a medical review officer. Buric said MacFenerstein has indicated he will no longer participate in Mayfield's case.