title: TSH-lowering effect of metformin in type 2 diabetic patients: differences between euthyroid, untreated hypothyroid, and euthyroid on L-T4 therapy patients.
abstract: OBJECTIVE
  To assess the interplay between metformin treatment and thyroid function in type 2 diabetic patients.
  
  
  METHODS
  The acute and long-term effects of metformin on thyroid axis hormones were assessed in diabetic patients with primary hypothyroidism who were either untreated or treated with levothyroxine (L-T4), as well as in diabetic patients with normal thyroid function.
  
  
  RESULTS
  No acute changes were found in 11 patients with treated hypothyroidism. After 1 year of metformin administration, a significant thyrotropin (TSH) decrease (P < 0.001) was observed in diabetic subjects with hypothyroidism who were either treated (n = 29; from 2.37 +/- 1.17 to 1.41 +/- 1.21 mIU/l) or untreated (n = 18; 4.5 +/- 0.37 vs. 2.93 +/- 1.48) with L-T4, but not in 54 euthyroid subjects. No significant change in free T4 (FT4) was observed in any group.
  
  
  CONCLUSIONS
  Metformin administration influences TSH without change of FT4 in patients with type 2 diabetes and concomitant hypothyroidism. The need for reevaluation of thyroid function in these patients within 6-12 months after starting metformin is indicated.
authors.affiliation: Internal Medicine and Endocrinology Unit, Department of Medical and Surgical Sciences, University of Brescia, Brescia, Italy. cappelli@med.unibs.it
authors.forename: Carlo
authors.initials: C
authors.lastname: Cappelli
authors.forename: Mario
authors.initials: M
authors.lastname: Rotondi
authors.forename: Ilenia
authors.initials: I
authors.lastname: Pirola
authors.forename: Barbara
authors.initials: B
authors.lastname: Agosti
authors.forename: Elena
authors.initials: E
authors.lastname: Gandossi
authors.forename: Umberto
authors.initials: U
authors.lastname: Valentini
authors.forename: Elvira
authors.initials: E
authors.lastname: De Martino
authors.forename: Antonio
authors.initials: A
authors.lastname: Cimino
authors.forename: Luca
authors.initials: L
authors.lastname: Chiovato
authors.forename: Enrico
authors.initials: E
authors.lastname: Agabiti-Rosei
authors.forename: Maurizio
authors.initials: M
authors.lastname: Castellano
mesh_terms: D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy*; D006801:Humans; D007004:Hypoglycemic Agents / Q000009:adverse effects* / Q000627:therapeutic use; D007037:Hypothyroidism / Q000503:physiopathology*; D008687:Metformin / Q000009:adverse effects* / Q000627:therapeutic use; D013959:Thyroid Diseases / Q000188:drug therapy / Q000503:physiopathology*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000627:therapeutic use; D013995:Time
chemical_list: D007004:Hypoglycemic Agents; D013972:Thyrotropin; D008687:Metformin; D013974:Thyroxine