Magic Mouthwash is a compound made up by the pharmacist and can also contain morphine which is a fast acting pain killer. Codiene is a moderate pain killer and probably not up to the task of mitigating mouth sore pain.. The mouthwash is only for short term pain anyway, incidentally, don't swallow it - it is a "swish & spit" application. For long term pain, time release Fentanyl or Morphine patches work very well. proper pain management is a combination of long term and short term (for breakthrough pain) meds. It is also a balance between the 2. if he is taking too much short term meds, they will adjust the dose rate of the long term meds upward accordingly.