I've read that some can metabolize meds faster than others - so those would need more to cover the pain better.
I don't know if there are tests to prove that or not..

Do you feel like you are on an even keel with these med dosages?
Is your pain under control fairly well with these meds?
Is your blood work being checked often?

Have you looked tall these up to read more about them & any side effects?
http://www.drugs.com/condition/pain.html


What kind of pain do you have? mainly nerve, muscles?
Are you having any PT or other therapies also?