Jeremy Mayfield was suspended indefinitely by NASCAR on Saturday for failing a random drug test, becoming the first driver to violate a toughened new policy that went into effect this season.

Mayfield tested positive for a banned substance last weekend at Richmond International Raceway.

“In my case, I believe that the combination of a prescribed medicine and an over-the-counter medicine reacted together and resulted in a positive drug test,” Mayfield said in a statement. “My doctor and I are working with both Dr. (David) Black and NASCAR to resolve this matter.”

Black is the CEO of Aegis Sciences Corp. in Nashville, Tenn., which runs NASCAR’s testing program.

NASCAR spokesman Jim Hunter would not reveal what banned substance Mayfield used, but Hunter said it was not an alcohol-related offense.

“There is no place for substance abuse in our sport,” Hunter said.

NASCAR also suspended two crew members for failed tests at Richmond.

Tony Martin, a crew member for the car John Andretti drove last weekend at Richmond, and Ben Williams, a crew member for the Nationwide Series car Matt Kenseth drove last weekend, were both suspended indefinitely.

Mayfield, who is driving a car this season he owns himself, failed to qualify for Saturday night’s Sprint Cup race at Darlington Speedway.

NASCAR said Mayfield was randomly tested last Friday in Richmond. The Aegis lab discovered the positive “A” sample Tuesday and notified Mayfield. Two days later, the lab told NASCAR of the failed test.

Mayfield, who participated in both of Friday’s practice sessions at Darlington, asked Friday for his backup “B” sample to be tested. That, too, came back positive, and he was told by Aegis officials Saturday afternoon.

Black said he spoke with Mayfield, who can return to NASCAR only after he completes a “path for reinstatement” that’s tailored to each individual. The process, which can include rehab, varies depending on the substance.

The suspension, which cannot be appealed, applies to Mayfield’s roles as owner and driver of the No. 41 Toyota.