Introduction & Objective: Metabolic control in adolescents with type 1 DM who are in pubertal period will be impaired, thus finding a therapeutic strategy such as adding metformin to insulin to reduce insulin resistance will be useful in blood glucose control and metabolic state improvement.

Materials & Methods: This was a randomized double blind placebo controlled 3-month trial metformin therapy in 32 adolescents with type 1 DM. These patients were divided in two groups of metformin and placebo and treated with metformin and placebo for 3-months. Their HbA1C, FBS, Insulin dosage, TG, Cholesterol, and LDL were measured at the initiation and end of the treatment.

Results: After the study there was a significant improvement of FBS and TG in metformin group versus placebo group (P=0.02 and P=0.028 in order). But, there was not significant difference in other variables such as BMI, insulin dosage, HbA1C, Cholesterol and LDL between the two groups.

Conclusion: Metformin treatment in teenagers with type1 DM who are in pubertal period will improve the control of FBS and lowers TG but has not any significant effect on HbA1C, BMI, insulin dosage, Cholesterol and LDL.