The New York Daily News reported news of the relapse Thursday.
On Friday, a source told ESPN's Tim Keown that Hamilton's relapse involved alcohol and a one-time use of cocaine, and when Hamilton realized a drug test, which is administered three times a week, would come out positive, he self-reported his relapse.
Hamilton has a well-documented history of substance abuse problems dating to his days in the minor leagues, when he was suspended from baseball from February 2004 to June 2006, for issues related to cocaine and alcohol addiction.
The Angels confirmed that he met with MLB officials in New York on Wednesday about a disciplinary issue but offered no specifics as to the nature of any offense.
"We're all waiting for some information to come out of New York," Angels manager Mike Scioscia said Thursday. "He obviously went up there for a meeting, and we'll see how everything unfolds. But right now, we're just in a holding pattern like everyone else."
The Los Angeles Times earlier reported the meeting between Hamilton and the league.
Hamilton's agent, Michael Moye, did not return a call seeking comment Wednesday. MLB spokesman Pat Courtney declined to comment.
The Daily News report follows tweets by Jon Heyman of CBSsports.com on Wednesday in which he wrote: "Hear hamilton had relapse. Believe occurred a couple months back. Involved at least cocaine." In another tweet, Heyman wrote, "There's no word of a failed test. Word is, Hamilton told mlb about relapse."
Hamilton, who underwent shoulder surgery earlier this month and is expected to be out until at least May, has not been with the team at spring training in Arizona. The Angels have permitted Hamilton to stay at a friend's house in Houston while he rehabs from the surgery, even though players typically stay with their teams in those situations.
One of the conditions of Hamilton's reinstatement in 2006 was that he undergo drug testing three times a week. He had alcohol relapses in 2009 and 2012, bouncing back in between to make back-to-back trips to the World Series with the Texas Rangers and win the 2010 American League MVP award.
He also took off the 2003 season, citing personal reasons. He did not play professional baseball from July 2002 to July 2006.
Hamilton signed a five-year, $125 million deal with the Angels before the 2013 season.
Some of his former teammates with the Rangers, as well as general manager Jon Daniels, were saddened by the report about a relapse.
"It's just sad news," former teammate Michael Young told the Fort Worth Star-Telegram. "I think about a friend and a former teammate, and a guy with a family. I empathize. It just has to be a very tough situation for Josh right now.
"Hopefully, he has a lot of good people around who are helping him through a tough time. But I hope he also knows that there are people that he's played with that care about him, that care about his future and are willing to help in any way they can."
Said Daniels: "Forget baseball. My first thought was that I hope for the best for him as a person."
Roy Silver, a baseball academy owner who helped Hamilton about a decade ago, said that when Hamilton came to his facility nine years ago, there was no question about his level of inspiration back then.
"He was inspired. But he was driven to get back on the field because he was getting out of the gutter." Silver said. He told a story about how Hamilton was so driven back then, he'd dive for fly balls when Silver was just hitting him fungoes "like he was a 10-year-old kid. It was fun to watch."
Silver said Hamilton has never really grasped what an incredible talent he has.
"You can't get in his mind and understand what a big leaguer is going through," he said. "It's just a different place. ... To be as good as he is and not understand it -- he doesn't really understand it. Guys who do it at that level, it's just normal to them."
He said he and Hamilton text and talk "about four or five times a year." They've swapped a couple of "how are you"-type texts in the last couple of days, but "I'm giving him space," Silver said.
"We'll talk in the future. That's basically it. Whenever he's ready."
ESPN.com's Jerry Crasnick and Jayson Stark contributed to this report.