As many questions have been asked in regard to metformin here on this site, as it is drug to regulate Type 2 Diabetes, upon starting drug, I have been taking since now at least four year time with no side effect. I am 23yo Japanese male. I now just begin to get watery (or near watery) dark brown diarrhea that is profuse and explosive. Even causes sometime fecal incontinence public embarrassment with me. Why suddenly this change? I had been led to believe that diarrhea was only for beginner user of Metformin. This is terrible! Much thank you!