These side effects usually go away soon after the metformin is started and occur less often if metformin is taken with food. Another possible problem with metformin is a rare but serious condition called lactic acidosis, when your tissues do not get enough oxygen to survive. To avoid this problem, metformin should not be given to people with kidney or liver disease, severe heart failure, or a history of alcohol abuse. Skin rashes are rare. The platelet inhibition hardly has any clinical disadvantages.
Most cases affect individuals with risk factors, especially impaired renal functions.
The risk of a lactic acidosis under metformin is no greater than the risk of a severe hypoglycemia under sulfonylureas.