Swimmer Michael Phelps, who has won more gold medals than anyone in Olympic history, acknowledged Sunday he had engaged in "regrettable" behavior and shown "bad judgment" after a photo of him smoking what appears to be marijuana from a glass pipe was published in a British tabloid over the weekend.
Marijuana is classified by the World Anti-Doping Agency, which oversees Olympic and international drug testing, as a banned "in-competition" substance, meaning Phelps is unlikely to face any punishment or suspension.
"I engaged in behavior which was regrettable and demonstrated bad judgment," Phelps said in a statement released by Octagon, his management firm, and posted on his Facebook site. "I'm 23 years old, and despite the successes I have had in the pool, I acted in a youthful and inappropriate way, not in a manner that people have come to expect from me. For this, I am sorry. I promise my fans and the public -- it will not happen again."
Marketing experts said the incident should have minimal effect on Phelps' multimillion-dollar sponsorships because of his quick apology.
The photo in the News of the World tabloid of Phelps -- who won eight gold medals at the 2008 Summer Olympics in Beijing -- shows him with his cap on backward, holding the pipe to his mouth with his right hand while lighting it with his left. The tabloid says it was snapped at a party at the University of South Carolina in November. Phelps attended a Gamecocks football game against Arkansas in November and received a standing ovation from the crowd at halftime.
Phelps has never failed a drug test during his career and was one of several American athletes who volunteered to undergo additional testing to dispel any suggestions that he might be benefiting from performance-enhancing drugs.
"We'll evaluate whether he remains in that program," said Travis Tygart, head of the U.S. Anti-Doping Agency.
Marijuana, though not considered performance-enhancing, was added to the International Olympic Committee's list of banned substances after the 1998 Olympics. Its use among Olympic athletes became a matter of public debate after Canadian snowboarder Ross Rebagliati tested positive after winning a gold medal in Nagano, Japan, in 1998. Rebagliati was initially stripped of his medal, but in the end kept it because marijuana was, at the time, not on the list.
An athlete is subject to WADA sanctions only for a positive test that occurs during competition periods, according to David Howman, executive director of WADA.
But he suggested U.S. swimming officials or the sport's world organization, FINA, could punish Phelps if there is "sufficient evidence to indicate possession, supply or distribution."
FINA and International Olympic Committee officials said they would not comment on the matter until today.
Phelps hasn't swum competitively since the Olympics and just recently started training again with an eye on the 2009 world championships. He said recently that he was hoping to appear at the Austin Grand Prix from March 5-7.
His coach, Bob Bowman, said in a statement that "Michael has issued his statement. He regrets his behavior and I'm sure he'll learn from this experience. I'm glad to have him back in training."
The United States Olympic Committee, which last week named Phelps its male athlete of the year, issued a statement saying it was "disappointed" in Phelps' behavior.
"Michael has acknowledged that he made a mistake and apologized for his actions," it said. "We are confident that, going forward, Michael will consistently set the type of example we all expect from a great Olympic champion."
This isn't Phelps' first public stumble. In 2004, when he was 19 and a few months removed from winning six gold medals at the Olympics in Athens, he was pulled over by authorities after rolling through a stop sign and charged with driving while intoxicated. Phelps publicly apologized, calling it an "isolated incident." He agreed to a plea deal with prosecutors that sentenced him to 18 months of probation.
The Associated Press contributed to this report.