As reported from in vivo testing, GLP-1R agonists, specifically liraglutide, can induce hyperplasia in thyroid C cells and tumors in primates; therefore, it is recommended to avoid GLP-1R agonists in patients with a past history or family history of medullary thyroid cancer or multiple endocrine neoplasia 2 [88,89,90]. This evidence concerns the gene GLP1R and medullary thyroid gland carcinoma.