Tailored metformin treatment will consist of incremental doses regimen starting from a dosage of 850 mg daily (one tablet daily) with a weekly increase up to 2550 mg daily (three tablets daily). The dosage of metformin will be reduced according to the appearance of serous or affecting compliance drug-related side effects. Conversely, non-tailored metformin treatment consisted of fixed doses regimen of 850 mg twice daily. For both groups, the treatment will be of six months.