In this study, 30 patients will be included divided in two arms. Investigators and patients will not know the treatment used (double blind).
Arm 1: Metformin 1000mg twice a day (2000 mg/day), during 12 weeks. Arm 2: Placebo 1000mg twice a day (2000mg/day), during 12 weeks.
At the end of the study, patients will be followed-up 8 weeks more to control the appearance of adverse effects.
