Tirzepatide Mechanism of Action

Dual receptor engagement

Tirzepatide binds and activates two receptors: the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R). Both are class B (secretin-family) GPCRs coupled predominantly to Gαs and expressed on overlapping but non-identical cell populations — β-cells, α-cells, adipocytes, vagal afferents and multiple central populations.^[6][8]

GLP-1 receptor arm

At GLP-1R, Tirzepatide couples predominantly to Gαs, elevates intracellular cAMP, activates protein kinase A and EPAC2, and drives glucose-dependent insulin secretion, α-cell suppression and slowed gastric emptying — the classical GLP-1R pharmacology.^[7]

GIP receptor arm

At GIPR, Tirzepatide reproduces GIP-like Gαs / cAMP signalling. GIPR is expressed on pancreatic β-cells (where it complements GLP-1-driven insulin exocytosis), on α-cells, and — importantly — on adipocytes, where GIP signalling modulates lipid handling and insulin sensitivity.^[9][8] The GIP-adipocyte axis is one of the distinguishing features of dual-agonist pharmacology compared with GLP-1 mono-agonists.

Biased agonism at GLP-1R

Willard and colleagues reported that Tirzepatide engages GLP-1R with reduced β-arrestin recruitment relative to native GLP-1 — an imbalanced or biased agonism profile.^[2] β-arrestin recruitment contributes to receptor internalisation and pathway-specific signalling; reduced arrestin engagement may slow receptor desensitisation and change the balance of downstream outputs. The therapeutic consequence of this bias is an active research question.

cAMP signalling

cAMP is the primary second messenger downstream of both receptors. It activates protein kinase A (PKA), which phosphorylates ion channels, exocytotic machinery and transcription factors, and it engages the PKA-independent effector EPAC2, which contributes to glucose-dependent insulin exocytosis.^[7] β-arrestin is recruited at both receptors but, per the biased-agonism data above, less efficiently at GLP-1R than native GLP-1.^[2]

Central appetite regulation

GIP and GLP-1 receptors are both expressed in the hindbrain (nucleus of the solitary tract, area postrema) and in hypothalamic populations (POMC and NPY / AgRP neurons in the arcuate nucleus) that integrate satiety signalling. Dual-receptor engagement is hypothesised to broaden central coverage relative to GLP-1 mono-agonists, contributing to reported effects on food intake in preclinical models.^[9]

Metabolic signalling summary

• Glucose-dependent stimulation of insulin secretion (β-cell — both receptors).
• Suppression of glucagon secretion (α-cell — glucose-dependent, both incretin pathways contribute).
• GIP-mediated modulation of adipocyte lipid handling.
• Slowed gastric emptying (GLP-1 arm — vagally mediated).
• Reduced food intake through integrated central circuits.

Related reading: Tirzepatide monograph, What is Tirzepatide, Tirzepatide mechanism of action, Semaglutide monograph, Retatrutide monograph, GLP-1 receptor explained, Triple agonists explained, Albumin binding, Incretin effect, Research Use Only and Testing & Quality Control.