In a statement, the No. 4 Longhorns did not identify the friend but said the person had no connections to the school.
Pittman, a senior, was already going to miss Saturday's game against Arkansas State with a shoulder injury. He will be eligible to return Sept. 22 against Rice.
"I want everyone to know I'm really sorry," Pittman said. "It was an honest mistake and I'll do everything I can to make up for it."
Pittman has 69 catches for 1,206 yards and nine touchdowns over the last two seasons.
Pittman is the latest Texas player suspended for off-the-field issues this summer. Linebacker Sergio Kindle and defensive end Henry Melton are also suspended three games after both were charged with DWI.
A third player, freshman linebacker Dre Jones, was suspended indefinitely after being charged with aggravated robbery. A fourth player, former safety Robert Joseph, was charged in the same incident. Joseph had already left the team after being arrested in a separate incident over the summer.
Copyright 2007 by The Associated Press