GLP-1 is secreted by L cells in the mucosal layer of the ileum and colon. It primarily promotes insulin secretion in a glucose-dependent manner by binding to specific receptors on the membrane of pancreatic β-cells. This means that when blood glucose levels rise, GLP-1 secretion increases, stimulating insulin release and thereby lowering blood sugar levels.
GLP-1 is widely distributed in various organs and tissues throughout the body. However, natural GLP-1 is rapidly degraded by the enzyme dipeptidyl peptidase-4 (DPP-4) in the body, resulting in a half-life of less than 2 minutes.

Dulaglutide is a fusion protein of glucagon-like peptide-1 (GLP-1) analogues and Fc, which belongs to GLP-1 receptor agonist. It promotes insulin release and inhibits glucagon secretion to lower blood sugar by stimulating GLP-1 receptor. In addition, postprandial blood glucose increase is reduced by delaying gastric emptying. 
Dulaglutide only needs to be injected once a week; and its unique mechanism of action makes it less likely to cause hypoglycemic events when used alone.