Johnson, 30, an eight-time winner on the PGA Tour who tied for 12th two weeks ago at the Open Championship, released a statement through his management company after having withdrawn from the WGC-Bridgestone Invitational earlier this week.
"By committing the time and resources necessary to improve my mental health, physical well-being and emotional foundation, I am confident that I will be better equipped to fulfill my potential and become a consistent champion," Johnson said.
Johnson's agent, Davis Winkle, said neither he nor Johnson would have any further comment.
The PGA Tour said in a statement that it had nothing to add "but we wish him well and look forward to his return to the PGA Tour in the future."
The PGA of America has been told by Johnson's representatives that he won't play in the Ryder Cup at the end of September. If that holds, the players on the points list would move up a spot. Patrick Reed is currently 10th in the standings, with the top 9 after next week's PGA Championship automatically making the team. Captain Tom Watson has three at-large picks to make on Sept. 2.
Johnson currently is fifth on the points list, making him a virtual lock to make the team.
"We will certainly miss Dustin Johnson at Gleneagles, and we wish him the best," Watson said in a statement. "As one of the longest hitters in the game with an undefeated record of 3-and-0 at Medinah in 2012, he has clearly been an asset for the United States team.
"That said, the United States is a team with an abundance of talent," Watson said. "I am looking forward to teeing it up alongside those players in the PGA Championship at Valhalla, and finding out along with everyone else, which players qualify for the team based on points."
Last year, Johnson and girlfriend Paulina Gretzky, the daughter of NHL Hall of Famer Wayne Gretzky, announced their engagement. Earlier this year, she appeared on the cover of Golf Digest, a controversial selection that upset some members of the LPGA Tour.
Johnson is generally regarded as one of the most talented players in the game. His eight victories are more than any player his age. He missed the cut last weekend at the Canadian Open and won't play in next week's PGA Championship.
Two years ago, Johnson missed significant time with a back injury, announcing it on the eve of the Masters. He did not play for three months from the WGC-Cadillac Championship until the Memorial Tournament.
Players at the Bridgestone Invitational said they were surprised by the announcement.
"If anything, I just hope this is the start of something really, really positive," Zach Johnson said. "And I don't know what happened. I don't know what the specifics are, nor should I know. That's none of my business. I feel for him."
Justin Rose called it "big blow for the tour."
"He's always been a charismatic player and popular player out here," Rose said. "He's not going to play in the Ryder Cup. That will be a blow for the American team. Just wish him well, whatever he's facing right now. Can't be easy for him."
Johnson played poorly in his first Ryder Cup at Wales, not winning a match until the final day in singles. He was the only American to go undefeated last time in Medinah, winning both fourballs matches with Matt Kuchar and handily beating Nicolas Colsaerts in a singles match.
"I'll tell you what, you always want guys with that kind of power to play on any team," Tiger Woods said. "I've been his partner in the Presidents Cup in Australia, and the firepower that he has, it's pretty cool to be around. It's not too often you see the guy carry the ball 320 (yards) without even trying, and then when he steps on it, he can hit it even further. When he gets it going, it's awfully impressive."
Information from The Associated Press was used in this report.
Impact Of Dustin Johnson's Absence
Mark Schwarz and Bob Harig break down the impact Dustin Johnson taking a leave of absence will have on the Ryder Cup team and his future.