Former Univ. of Alabama running back Ahmaad Galloway -- who played for Tide from 1999 to 2002 -- died from an accidental overdose ... officials tell TMZ Sports.
The Office of the Medical Examiner in St. Louis said Friday the ex-football player died from a lethal combination of fentanyl, ethanol and xylazine.
He was just 42 years old.
As we reported, Galloway was found dead in his home on Jan. 9 ... after he failed to show up for his gig as an eighth grade teacher at Compton-Drew Middle School in St. Louis.
The school's principal, Susan Reid, said at the time he showed no signs of trouble leading up to his death ... and had just attended a students' basketball game days prior to his passing.
In his three years at 'Bama, Galloway rushed for 1,830 yards and 17 touchdowns. He went on to be picked by the Denver Broncos in the seventh round of the 2003 NFL Draft -- but never logged an official stat in his pro career.
RIP.