Josh Gordon's substance abuse issues run deeper than weed ... so says Dr. Drew, who tells TMZ Sports he believes the WR is dealing with something far more serious than pot.
Gordon announced Thursday he's stepping away from football to focus on his mental health -- but the NFL says he violated the league's substance abuse policy, once again.
Dr. Drew says it just can't be a weed issue that the Patriots WR is dealing with ... telling us Josh is most likely hooked on something much more powerful.