The most common side effects are anorexia, dyspepsia, flatulence, headache, metallic taste, nausea and vomiting as well as weight loss. Metformin interferes with the absorption of Vitamin B12 by competitive inhibition of calcium-dependant binding of the intrinsic factor-Vitamin B12 complex to its receptor; anemia in predisposed individuals may be possible. Rarely, megaloblastic anemia and hypoglycemia occur. However, hypoglycemia does not usually occur with use of metformin unless predisposing factors are present, such as unusual fasting, concurrent use of other antidiabetic agents, or toxic doses of metformin. Lactic acidosis is a potentially fatal complication. However, the risk is minimal with use of metformin unless in patients with contra-indications to therapy. Patients usually presented not with symptoms of lactic acidosis but rather with acute symptoms of other problems that resulted in metformin accumulation because of renal function impairment or failure and in conditions such as myocardial infarction or hepatic disease.
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