Matt,

I think you are going to have to do a better job interviewing...

Most people who say they are allergic to codeine simply get bad side
effects like: nausea, itching, hot/cold flashes & sweating...IE: Typical
opioid drug side effects.  They may indeed not be able to tolerate
codeine, at least not without taking something for nausea, but they
aren't truly allergic to it, they also may not have liked the dysphoric
head effects, or felt it didn't give them very good relief, it also has
a reputation as a rather weak drug.  You need to ask them what
specifically happened when they took it. Did they break out in hives?
Trouble breathing? Rashes? ...etc things that would indicate a true
allergy.  I don't know the percentage of true cross reactions, one of
the Rph's here probably will.

There are people out there who simply don't want it again and just list
it as an allergy for that reason. While not completely honest with their
doctor, if they had a miserable time with it before that is probably
good enough reason to use something else.

Then you come across the folks who are allergic to everything but
dilaudid injections, and that is a different problem. >G<