A Durham, N.C., court clerk confirmed to several media outlets that the charges were dropped.
Hairston was scheduled to have a court hearing in August after being arrest June 5 on a misdemeanor marijuana charge after being stopped. He had also been charged with driving without a license, which was also dismissed.
Hairston was arrested during a license checkpoint in Durham while driving a rented SUV along with two passengers. All three were charged with misdemeanor marijuana possession.
Officers also found a 9mm handgun outside the vehicle.
The rental driven by Hairston was linked to Haydn "Fats" Thomas, a convicted felon who is facing a drug charge.
The school was aware that the charges against Hairston were dropped but it is not clear if Hairston will face any discipline from the team. Coach Roy Williams did say last week that Hairston would face "severe consequences."
The school is investigating if Hairston or any other players have improper ties to NBA agent Rodney Blackstock, who is from Hairston's hometown of Greensboro.
Hairston averaged 14.6 points per game for the Tar Heels last season as a sophomore.