You really should do some more reading before getting into drugs like these. That FAQ I linked can help you with that question, and it's just good, interesting reading anywho. Most folks don't like polystyrex, as it lasts longer and is less potent, they prefer Hbr, though your syrup should be safe if the only listed ingredient is DXM. The stuff for kids costs the same and contains less drug than the adult formula, so most folks drink that.