BALTIMORE (AFP) - Michael Phelps, an 18-time Olympic swim champion with an eye on Rio, said Sunday he would take a break from his comeback to get help after a drink driving arrest.

Phelps was charged Tuesday with driving under the influence of alcohol in Baltimore as well as excessive speed and crossing the centre line while driving inside a tunnel in his hometown.

"The past few days have been extremely difficult. I recognize that this is not my first lapse in judgement, and I am extremely disappointed with myself," Phelps said Sunday in a series of Twitter postings. "I'm going to take some time away to attend a program that will provide the help I need to better understand myself.

"Swimming is a major part of my life, but right now I need to focus my attention on me as an individual and do the necessary work to learn from this experience and make better decisions in the future."

Phelps, whose blood-alcohol content of .14 was nearly twice the legal limit of .08, had been arrested for drink driving in 2004 at age 19 and was sentenced to 18 months of probation. He also took to Twitter to apologise after his arrest.

"I understand the severity of my actions and take full responsibility," Phelps told his 1.6 million Twitter followers earlier this week. "I know these words may not mean much right now but I am deeply sorry to everyone I have let down."

Phelps, now 29, is the most decorated athlete in Olympic history with 22 medals, won three gold medals at the Pan Pacific Championships in late August in Australia to show his efforts ahead of the Rio de Janeiro Olympics in two years were on pace to produce more success. He retired after the London Games only to launch a comeback earlier this year.