Despite the encouraging results of GLP-1/glucagon co-agonism in experimental models, different GLP-1 and glucagon co-agonists have shown various levels of efficacy and tolerability in people with obesity and/or T2D, in early phase clinical trials, which may be explained by the different ratio of GLP-1 to glucagon activity between the different molecules [65]. This evidence concerns the gene GLP1R and type 2 diabetes mellitus.