polymath
Bluelight Crew
To me it seems that codeine actually takes effect a lot faster than orally dosed morphine (in form of poppy pod or seed extract). It's probably that it's absorbed faster from the stomach and the time it takes for it to be converted to actives in the liver is not as significant a factor. Carbonated beverages make the absorption faster as Nicomorphinist said. The effect from some dose of codeine can be quite unpredictable (at least if you don't have significant tolerance), it's possible that the same amount had only a mild effect yesterday and today it gets you really high.