US swimmer Michael Phelps will not face charges over a photograph apparently showing him smoking cannabis.
Phelps, 23, was suspended for three months by USA Swimming after an image of him inhaling from a glass pipe at a party in South Carolina was published.
A British paper said the picture was taken three months after he won eight gold medals at last year's Olympics.
Phelps has not said whether he was using drugs.
Richland County Sheriff Leon Lott told the Associated Press that although he was not going to press charges, the authorities had had to investigate after the image was released.
The sheriff said there had not been sufficient evidence to charge him based on the photograph from the party, held near the University of South Carolina in November.
He said: "We had a photo and him saying he was sorry for inappropriate behaviour. He never said, 'I smoked marijuana.' We didn't have physical evidence."
In a statement released after the sheriff's decision, Phelps said: "I'm glad this matter is put to rest. But there are also some important lessons that I've learned.
"For me, it's all about recognising that I used bad judgement and it's a mistake I won't make again. For young people especially - be careful about the decisions you make."
Phelps said he appreciated the support shown to him by his family and fans.
"I will move forward and dive back into the pool, having put this whole thing behind me."
USA Swimming, the national swimming federation, banned Phelps from competitive swimming for three months, although he has never tested positive for banned substances.
The International Olympic Committee accepted an apology from him, saying it had no reason to doubt his sincerity or his commitment to being a role model.
The swimmer has, however, lost the backing of cereal maker Kellogg, with the firm saying it would not renew its sponsorship deal with him when it comes to an end.