Definitely talk to your pharmacist about what binders and buffers are used by various manufacturers of norco. Your pharmacist is probably the best person to talk to about all this. Then you'll need to take what you learn to your doctor so he can note on your prescriptions that you can't tolerate Manufactuer A's product. If you can figure out what ingredient is causing the trouble, you'll need to get that information into your medical record and probably make that information available to your insurance company as well. Please let us know what you discover!
I'm confused about why you want off the pills since you have legitmate pain, they seem to work well for you and you don't abuse them. I've been tapering off fentanyl for quite a while. It's very slow, but I'm going in the right direction. Have patience and let your body adjust to each new decrease. Try to set reasonable goals and don't beat yourself up if you can't stick to a particular schedule.
Different color pills are made by different manufacturers, and different manufacturers use different inert ingredients to make their pills. I have a friend who cannot take meds made by a certain manufacturer because they use lactose as a binder when they make their tablets and she is HIGHLY lactose intolerant. Just the little bit that is used to make the pills is enough to give her all kinds of bad symptoms so she cannot take pills made by that manufacturer.
This might be the case with you. Even though the active ingredient is the same in pills made by different companies, the matrix of the pills is a little bit different from manufacturer to manufacturer and, depending on how sensitive our bodies are to these differences, that could be all that is necessary to cause an adverse reaction.
The best thing I can tell you is that you should find out who makes the white pills, and when you need to get another prescription filled for them, shop around and ask the various pharmacies in your area who manufactures their Norco. Tell them why you want to know and they shouldn't have a problem telling you. This way you can know before you even drop off the scrip that the pills you get will be the ones you need.
Ghilly