Treatment Side Effects Known adverse effects associated with metformin are primarily gastrointestinal (diarrhea, nausea, vomiting, abdominal bloating, flatulence, anorexia), hematologic (reduced vitamin B12 levels and, rarely, megaloblastic anemia), and the rare possibility of lactic acidosis. Known adverse effects associated with rosiglitazone are primarily hematologic (decline in hemoglobin and hematocrit) and fluid retention and edema. Hepatic toxicity has not been observed with rosiglitazone. Potential risks of the lifestyle intervention are minor and include temporary muscle soreness and injuries associated with physical activity and slight hunger when dieting.