Dulaglutide is engineered as a GLP-1 Fc-fusion pharmacophore that does not enter target cells in the manner of a small molecule but instead distributes systemically after subcutaneous injection, reaching pancreatic islets, gastrointestinal enteric neurons, vagal afferents, and hypothalamic–brainstem circuits via the circulation. Its large molecular format — two identical disulfide-linked chains, each carrying an N-terminal modified GLP-1(7–37) analog covalently attached to the Fc portion of a modified human IgG4 heavy chain via a synthetic peptide linker — produces a ~59.7 kDa homodimer that resists rapid renal clearance. FcRn-mediated pharmacokinetic extension is the primary mechanism of prolonged exposure: the IgG4 Fc domain binds the neonatal Fc receptor (FcRn) in acidic endosomes after pinocytotic uptake, protecting the molecule from lysosomal degradation, and releases it at physiological pH, recycling it back to the circulation. This yields an elimination half-life of approximately five days and enables once-weekly subcutaneous dosing, with steady-state concentrations reached over approximately 2–4 weekly doses and an accumulation ratio of approximately 1.56.

GLP-1 receptor engagement is the initiating pharmacological event at all target tissues. GLP-1R is a class B GPCR with a two-domain architecture: an extracellular domain that binds the C-terminal helix of GLP-1 and a transmembrane domain that contacts the peptide's N-terminal region, enabling agonist-driven receptor activation. Upon ligand binding, GLP-1R couples to Gs, stimulating adenylyl cyclase and raising intracellular cAMP. This cAMP signal bifurcates into dual effector arms: protein kinase A (PKA), which phosphorylates ion channels and transcription factors, and Epac2, which activates Rap1 to support secretory granule priming and recruitment.

In pancreatic β-cells, GLP-1R agonism produces a glucose-dependent insulin secretory amplification that is mechanistically layered on top of the canonical triggering pathway. Glucose metabolism raises the cytosolic ATP/ADP ratio, closing ATP-sensitive K⁺ (K_ATP) channels and depolarizing the β-cell membrane, which opens voltage-dependent Ca²⁺ channels (VDCCs) and initiates Ca²⁺-dependent exocytosis of insulin granules. GLP-1R activation amplifies this by increasing L-type VDCC activity, augmenting Ca²⁺ influx, and by facilitating Ca²⁺-induced Ca²⁺ release (CICR) from intracellular stores. Beyond the canonical Gs pathway, β-arrestin-1 contributes a scaffolding role: β-arrestin-1 knockdown attenuates GLP-1–stimulated insulin secretion by ~40% without reducing total insulin content, indicating a signaling efficiency function independent of insulin biosynthesis. Because the amplification depends on prior glucose-driven depolarization, insulin release remains tightly glucose-dependent, limiting hypoglycaemia risk.

In the gastrointestinal tract, GLP-1R-mediated gastric emptying delay slows nutrient delivery to the small intestine, reducing the rate of postprandial glucose appearance. Like other GLP-1 receptor agonists, dulaglutide slows gastric emptying through vagal and enteric nervous system pathways. The largest emptying delay occurs after the first dose and then lessens with successive doses, consistent with tachyphylaxis. This pharmacodynamic attenuation also creates a mechanism-based drug–drug interaction: slowed gastric transit can reduce the rate of absorption of concomitantly administered oral medications.

Central appetite suppression adds a third major axis. Central GLP-1R agonist administration reduces food intake, with anorexigenic responses mediated by hypothalamic nuclei including the arcuate nucleus and hindbrain regions including the nucleus of the solitary tract (NTS). GLP-1R expression in vagal afferent neurons is important for regulating food intake and meal size, linking peripheral nutrient sensing to CNS satiety output. Dulaglutide's large ~63 kDa molecular weight may limit blood–brain barrier penetration relative to smaller GLP-1R agonists, which is proposed to contribute to its comparatively modest weight-loss profile.

A parallel hepatic lipid-remodelling pathway has been characterised in cellular models. In palmitate-stressed HepG2 cells, dulaglutide inhibits triglyceride accumulation and reduces lipid droplet–associated proteins PLIN1 and PLIN2. Mechanistically, it shifts hepatocyte lipid metabolism toward reduced lipogenesis — decreasing SREBP-1, ACC, FAS, and DGAT2 — while increasing expression of ATGL, p-HSL, SIRT1, p-AMPK, and PPARα, favouring fatty-acid oxidation. Functional knockdown experiments identify FAM3A as a required mediator: siRNA inhibition of FAM3A abolishes dulaglutide's suppression of triglyceride accumulation and abrogates downstream oxidative signalling.

These mechanisms converge on the clinical phenotype. Sustained GLP-1R agonism across the weekly dosing interval, enabled by FcRn recycling, amplifies glucose-stimulated insulin secretion, smooths postprandial glucose excursions via gastric slowing, reduces caloric intake via hypothalamic and vagal circuits, and limits hepatic lipid burden under lipotoxic conditions. In the REWIND cardiovascular outcomes trial, dulaglutide reduced major adverse cardiovascular events in patients with type 2 diabetes, consistent with the integrated metabolic and vascular effects expected from this multi-tissue pharmacology. Together, these molecular actions produce the observed HbA1c reductions, modest body-weight loss, and improved cardiometabolic risk profile that characterise dulaglutide's clinical benefit.