Have taken metformin and a slow release version (Glumetza). I realize many people take it, but I cannot. It clearly induces severe flank and lower back pain to such a severe degree that it is completely debilitating. Cannot get out of a chair or out of bed without much help. Pain levels of about 8 out of 10. Drug label lists this as a known side effect, but without percent affected, it is hard to know how common this really is... I think this needs to be corrected on product labels. Stopped taking it 4 days ago and relief is still minimal. It might induce this effect by altering electrolytes causing severe spasm/cramping of muscle groups. Stop taking it if you are affected as it is terrible.