Green-Beckham, Copelin and Boozer will serve a one-game suspension, Missouri spokesman Chad Moller said. Also serving one-game suspensions are freshman defensive linemen Harold Brantley and freshman tight end Brandon Holifield, who were present but not arrested, Moller said.
Green-Beckham was ESPN's overall third-ranked recruit in the nation last year and the top wide receiver prospect.
The players were sitting in a white Lincoln Navigator in a parking lot near Memorial Stadium shortly before midnight when a patrol officer approached and smelled marijuana. Green-Beckham was the driver, Capt. Brian Weimer said.
Each was arrested on a misdemeanor charge of possession of 35 grams or less of marijuana and released with a summons to appear in court next month. Under a 2004 ballot measure approved by city voters, possession of small amounts of pot in Columbia is treated as a low-level offense in municipal court similar to a traffic citation. Violators typically pay a fine of no more than $250 and receive community service in lieu of jail time.
The conviction is dropped if the offender stays out of legal trouble for another year, though repeat offenders and those with felony convictions are exempt.
Green-Beckham is Missouri's fourth-leading receiver with seven catches for 128 yards, including an 80-yard touchdown in last week's victory against UCF.
He is listed as a reserve but is often on the field in three- and four-receiver sets. He is the only player among the five to see meaningful action this season for Missouri (3-2, 0-2 Southeastern Conference). But much has been expected of the player known as DGB since he committed to Mizzou after a record-breaking career at Hillcrest High in the southwest Missouri city of Springfield, where he caught 75 touchdowns and compiled a national-record 6,353 receiving yards.
Before the suspension, offensive coordinator Dave Yost acknowledged that Missouri needs to target Green-Beckham more often.
"When you see it in practice all the time, he's so talented," Yost said. "We've just got to give him the ball more. We've got to give him more opportunities."
Brett McMurphy covers college football for ESPN. Information from The Associated Press was used in this report.