Michael Phelps reacts after his seventh place finish in the Men's 100 Meter Freestyle Final during the 2014 Phillips 66 National Championships at the Woollett Aquatic Center on August 6, 2014 in Irvine, California.
Michael Phelps opens up on alcohol use
00:52 - Source: CNN

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Michael Phelps talks about past alcohol use

The 18-time gold medalist admits he "doesn't know" if he's an alcoholic

Phelps is training for fifth Olympic Games at Rio 2016

CNN  — 

Michael Phelps, the most decorated athlete in Olympic history, has a checkered and well-publicized history with alcohol and drug use.

But is the 18-time Olympic gold medalist an alcoholic?

“I don’t know” was his candid response when the question was put to him. “I honestly don’t know.”

“I know I probably have moments where I have gone off the deep end where I shouldn’t.”

Read: What is Brazil worrying about with 100 days untl Rio 2016?

USA Swimming suspended Phelps for six months in 2014 for his second DUI arrest – the first coming 10 years earlier – and he was left out of the U.S. team for the 2015 World Championships.

Shortly afterward, Phelps attended a six-week, in-patient program to “provide the help I need to better understand myself.”

Read: Michael Phelps suspended by USA Swimming for six months

“I checked myself in because I think I was at a point in my life where something needed to change,” Phelps told NBC.

Read: Michael Phelps to ‘attend program’ after DUI charge

In 2009, a year after his historic eight-gold medal haul at the Beijing Olympics, a photo emerged of Phelps smoking marijuana, an incident he said made him realize who his real friends were.

The 30-year-old is training for what will be his fifth Olympic Games – Rio 2016.

“I want to retire how I want to retire – and I have a great opportunity to do that,” he said.