GCG and type 2 diabetes mellitus: In contrast, reports of the ability of GLP-1 to stimulate insulin secretion at elevated plasma glucose concentrations [22, 23] and its potential to lower plasma glucose concentrations in hyperglycaemic individuals with type 2 diabetes (Fig. 4) [22, 30–32, 41] led to an increase in the number of publications on GLP-1 (Fig. 7) and to the successful development of GLP-1 receptor agonists [1].