What is the difference between codeine and morphine?

Codeine is a 'pro drug'. by this I mean it is converted into another drug (morphine) and it is the morphine that kills the pain. There is a ceiling effect with this. most people can't convert more than 400mg of codeine in one go, any more is just a waste of money and more stress on your body. Codeine is addictive, constipating and does not mix well with tranquilizers, sleep aids, anti anxiety meds, so be very carefull if you are taking codeine with any other meds. drugs.com is a good place to check for drug interactions. I hope this helps.