Metformin Hydrochloride causes gastro-intestinal adverse effects such as anorexia, nausea and vomiting; absorption of various substances including vitamin B12 may be impaired. Patients may experience a metallic taste and there may be weight loss. Hypoglycemia is less of a problem with metformin than with the sulfonylureas. Lactic acidosis, sometimes fatal, has occurred but to a lesser extent than with phenformin and it is generally accepted that the lactic acidosis usually occurred in patients whose condition contraindicated the use of metformin, particularly those with renal impairment.