NEW YORK -- Ron Hornaday, the defending NASCAR Craftsman Trucks champion who is second in this year's standings, admitted using testosterone for more than a year before it was added to the sport's banned list.

Hornaday, 50, told ESPN he received shipments of testosterone and human growth hormone from December 2004 to January 2006, and that the drugs came from an anti-aging center that has been linked to drug-related scandals in the NFL and Major League Baseball.

Ron Hornaday used testosterone to treat a medical condition that later turned out to be a hyperactive thyroid.

Hornaday acknowledged taking testosterone when shown records from the Palm Beach (Fla.) Rejuvenation Center during an interview with ESPN at his home in North Carolina on Tuesday. He said the growth hormone was sent to his home for his wife's use.

He said he used the testosterone to treat a medical condition that later turned out to be a hyperactive thyroid.

Hornaday provided records to ESPN showing that the drugs were prescribed by doctors at the clinic within a day of his visit. He said he didn't see or speak with a doctor before receiving the prescription, and used it roughly every day for 13 months by rubbing a "pea-sized" amount onto his thigh.

"I couldn't see a difference," he said. "That's why I stopped."

NASCAR spokesman Ramsey Poston told ESPN that Hornaday had not informed anyone in the organization that he was using testosterone and that officials would seek more information from him before the Camping World RV Rental 200 in New Hampshire this weekend.

"It's hard to see whether it's a violation or not," said Poston, who noted that NASCAR's drug-testing policy prohibits the abuse of all drugs. "There are certain prescriptions that drivers can take, and we look at them on a case-by-case basis. If it's not putting other drivers at risk or enhancing performance -- and it's used as intended -- we'll make determinations as they come up."

Unlike the NFL and baseball, NASCAR does not have mandatory drug testing. It conducts tests when officials have "reasonable suspicion" that a driver or crew member is abusing prescription or other performance-enhancing drugs. Steroids and human growth hormone were specifically added to its list this year. Earlier this month, NASCAR chairman and CEO Brian France said the organization will announce an expansion to its drug-testing policy soon.