Last year I was given a generic version by my pharmacist. I asked him about it and he told me they were exactly the same. I didn't think any more about it and took them for the next 3 months. During that time I felt bloated and had much more flatulence and stomach discomfort than usual. When I spoke about it to my nurse she asked me if I was taking anything different and I told her about the metformin. She immediately got another prescription for Glucophage from my Doctor and said a few patients had had the same problems and there must be something slightly different about them.
My pharmacist doesn't like getting these for me and commented that they are more expensive although I don't see how it should affect him. He did try giving me the generic ones again but I pointed out to him that I must have the ones on the script. He still maintains there is no difference.