Table 5.

Effect of Antidiabetic Medications on Thyroid Function

Metformin

• Lowering TSH effect in subjects with high-normal serum TSH levels (TSH levels >2.5–3 mU/L) and in patients with overt and SHypo

• Reversible effect after discontinuation of metformin

• The TSH lowering effect of metformin can be observed in diabetic patients with thyroid disorder also when treating with T4

Sulfonylureas

• Goitrogenic activity of the first-generation sulfonylurea compounds

• Higher incidence of hypothyroidism in diabetic patients treated with the first-generation sulfonylureas compared with controls treated with diet alone or insulin

• No influence of second generation of sulfonylureas (glibenclamide and gliclazide) on TH metabolism

Thiazolidinediones

• Activation of PPAR-γ stimulates functional TSH receptor expression

• Increased recruitment and differentiation of orbital fibroblasts and stimulation of adipogenesis

• Increased risk of GO

Incretin mimetics

Animal models

• Activation of GLP-1 receptors on thyroid C cells

• Increased release of CT

• Increased C cell hyperplasia and adenomas

• Increased risk of medullary thyroid cancer at very high doses

Humans

• No effect on GLP-1 receptor activation

• No effects on serum CT levels

• No evidence for adverse effects

Insulin

• Enhanced levels of FT4 and reduced levels of T3

• Modulation of TRH and TSH secretion