Metformin as add-on to intensive insulin therapy in type 1 diabetes mellitus.

We aimed to evaluate the effect of adjuvant metformin to intensive insulin therapy in patients with type 1 diabetes mellitus (T1DM). A 10-year retrospective study in 2 cohorts was performed: the MET cohort (n = 181) consisted of patients with T1DM on adjuvant metformin for ≥6 months and the CTR cohort (n = 62) consisted of patients with T1DM who refused metformin (n = 25) or adhered to metformin for <6 months (n = 36). Data on glycated haemoglobin (HbA1c), body mass index (BMI) and daily insulin dose were recorded yearly. A third cross-sectional cohort, the REF cohort (n = 961), consisting of patients with T1DM not offered adjuvant metformin, was used as a reference for baseline comparison. At the study start, BMI was significantly higher and insulin doses were lower in patients in the MET cohort, while HbA1c levels were similar. In the first years of metformin therapy, small but non-significant decreases were seen in BMI and insulin dose in patients in the MET cohort, while after 10 years no persistent effect on HbA1c, insulin dose or BMI was seen. In conclusion, although metformin may have short-term effects on BMI and insulin dose when used as adjunct therapy in patients with T1DM, no long-term beneficial effects were observed when patients were followed for 10 years.