A South Carolina sheriff said he did not have enough evidence to charge Phelps.
Phelps, who won a record eight gold medals at last summer’s Beijing Olympics, has already admitted to “regrettable” behaviour after a photograph published in the News of the World showed the swimmer inhaling from a large pipe generally used to smoke marijuana.
The controversial photo was taken while Phelps was at a party last November at the University of South Carolina.
Phelps issued a statement today through his agency, Octagon, claiming he has learned a lesson from the incident.
“I’m glad this matter is put to rest,” Phelps said in the statement. “But there are also some important lessons that I’ve learned.”