Schwarber, 24, is hitting .171 just seven months after helping the Cubs to a World Series victory. Chicago is in second place in the National League Central.
"He took it really well. We're doing to hopefully reset him," Cubs manager Joe Maddon said. "Get him back up here with a fresh start. He was very professional about it. Understood it, entirely."
"At some point it felt like the right thing to do was give him a chance to hit the reset button," Cubs general manager Jed Hoyer said. "We got to the point mentally we thought he needs a mental break before he could come out of it."
As part of a series of moves, the Cubs will also put outfielder Jason Heyward on the disabled list with a cut on his hand. They are calling up outfielder Mark Zagunis from Iowa for his first taste of the majors. Pitcher Dylan Floro is also rejoining the team.
Heyward's stint on the DL is retroactive to June 19.
Heyward suffered the injury in the second inning of Sunday's game against the Pirates when he attempted to make a sliding catch on the warning track in foul territory.
There is no actual timetable," Maddon said regarding how long Schwarber will be with Iowa. "I don't anticipate it to be long. We'll see how it plays out."
After losing Dexter Fowler to free agency, manager Joe Maddon installed Schwarber in the leadoff spot to start the season. That lasted 36 games before he was dropped in the order and played against only certain right-handed pitchers. He hit .143 against lefties before being sent down.
"Hitting him lead off in 2017 didn't work. Whether or not that caused him to tailspin I have no way to answer that question," Hoyer said.
Schwarber hit .412 in the World Series last season with a .500 on-base percentage after missing all but three games of the regular season because of a serious knee injury. He was never cleared to play in the field, so he served as designated hitter for World Series games in Cleveland.
He was the fourth pick in the 2014 draft before making his debut for the Cubs in 2015.