Washington - Michael Phelps, the 18-time Olympic swimming champion arrested last week for drunk driving, was banned for six months by USA Swimming and dropped from the 2015 World Championships.
On Sunday, Phelps said on Twitter that he would be taking a break from swimming and "take some time away to attend a program" for treatment of unspecified personal issues.
In announcing sanctions against the Olympic superstar, USA Swimming executive director Chuck Wielgus said Phelps' actions required "significant consequences."
"Michael has publicly acknowledged the impact of his decisions, his accountability especially due to his stature in the sport and the steps necessary for self-improvement," Wielgus said.
"We endorse and are here to fully support his personal development actions."
The discipline meted out, which includes forfeiture of Phelps' funding from the federation for six months, is based on USA Swimming rules that prohibit conduct "detrimental to the image or reputation" of USA Swimming or the sport.
Phelps will still be allowed to train with his club, but cannot compete in USA Swimming-sanctioned competitions through March 6, 2015.
According to the federation, Phelps has agreed that he will not represent the United States at the World Championships on August 2-9 in Kazan, Russia.
The worlds were expected to provide a key measure of whether Phelps' comeback had him on course to challenge for more Olympic gold at Rio in 2016.
The 29-year-old retired after the 2012 London Olympics with a record 22 Olympic medals, but launched a comeback earlier this year.
He won three gold medals at the Pan Pacific Championships in late August in Australia to cement his place on the world championship team.
Phelps said in his statement on social media on Sunday that he was entering a program "that will provide the help I need to better understand myself."
He gave no further details of the issues he expected to deal with.
Police say a breathalyser administered after Phelps' arrest measured his blood alcohol level at .14, almost twice the legal limit of .08 in Maryland.
Phelps' trial is scheduled for November 19.