Promethazine/Codeine Syrup dosage?

SWIM had never really been interested in the world of painkillers as he'd seen them destroy lives, however codeine syrup always interested him and he finally was able to obtain an almost full 120 mL bottle from his friend.
SWIM is about 6'2 185lbs and has no tolerance to opiates. His one very good friend that is an avid PK user told him that a general rule of thumb is to never take more than 4 times the recommended dose at a time, which in this case is 5mL. Another friend of SWIM's (whom is a lot sketchier) laughed at the mere 20mL dose that was recommended and said 60mL would be a better dose for a first timer... Who is right? Thanks

 

20mL is probably the recommended dose if you're using it as a medicine. To get a high, you wanna do 60 mL, which is 2 ounces, which is how much my friends normally do. I've never done it but I know that's the normal dose.