Yeah its codeine(surprised this has not been mentioned yet). Idk about the standard dose of codeine in one "Purple Drank", but its probably not too crazily high, maybe a couple hundred mg. Consider codeine is 1/10th the strength of oxycodone, it takes a good amount to get a tolerant user high. Of course the promethazine in the syrup also produces effects that apparently synergize well with the codeine. Oh and don't forget the Jolly Ranchers.