I have been taking two drugs, Cardizem and Synthroid for 18 years. The mfg. has not changed in all that time and I have felt fine. The first of the year I upgraded my plan D policy and started to get my meds by mail. I had Cardizem left over from my original script and didn't start using the mail drugs until recently. I am having problems and I was wondering if all mfgs. are created equally. I have already had a problem with another one of their brands and had to switch back to Merck. Anyone had any issues with different mfgs. associated with their Ins. carrier???