still unknown. [ edit ] Gastrointestinal In a clinical trial of 286 subjects, 53.2% of the 141 who were given immediate-release metformin (as opposed to placebo ) reported diarrhea, versus 11.7% for placebo, and 25.5% reported nausea/vomiting, versus 8.3% for those on placebo. [ 71 ] Gastrointestinal upset can cause severe