OK so I will make this quick.  I just refilled my prescription for metformin er 500 mg tablets.  The new pills are made by a different manufacturer.  The old pills were slightly bigger and had different numbers on them.  The new pills which I have been taking for a few days now, are making my stomach more upset than the old ones, and causing more gas than the old ones. 

Why do I post this shit?

It is worth mentioning that if you are going to take a medication for the rest of your life, you may want to pay attention to the details of what you are taking.
I wish I would have paid attention to the brand name of my old metformin because I liked it better than the new stuff. Slight variations in formula can have big effects on your system.  This goes for other medications as well.  Pay attention to the brand name of the pills you are taking and make sure when you refill, ask for the brand name you are used to.

I have experienced this same thing with glipizide back when I was really sick with diabetes.  I changed brands without knowing it and the new brand plummeted my my numbers at a faster rate and caused me some really scary close calls with hypos. 

KNOW WHAT BRAND YOUR PILLS ARE AND PAY ATTENTION TO DOSAGES.  STAY ON THE SAME BRAND TO AVOID PROBLEMS.  NO ONE ELSE IS LOOKING OUT FOR YOU!