STOMACH IRRITATION, DIARRHEA
When starting metformin, around a third of people suffer some degree of stomach irritation, which usually resolves quickly. Only 3-10% of people in clinical trials experience symptoms severe enough that they stop taking the drug. Higher doses tend to cause more irritation, at least when comparing 500 milligrams (mg) to higher doses. Little difference is seen between doses of 1,000 mg and 2,500 mg.