Look on the bottle and see how many mgs codeine and promethazine are in each dose. Then, figuring that 150-450 mgs is a rec. dose (depenidng on tolerance and preference) take that many doses. Look up promethazine somewhere (maybe erowid.org) for potential effects, I don't know what it does. Also check for other ingredients in the syrup, such as guifenasin, which can cause negative side effects (diarrhea) when ingested in larger quantities.