Three receptors, one metabolic system
GLP-1, GIP, and glucagon are peptide hormones that each bind their own receptor within the body's metabolic signaling network. GLP-1 and GIP are incretins released from the gut, while glucagon is released from the pancreas. Understanding them as three distinct receptor targets is the foundation for understanding modern metabolic peptides, which are defined by which of these receptors they engage.
What each receptor does
The GLP-1 receptor is involved in glucose-dependent insulin signaling and gut–brain pathways. GIP (glucose-dependent insulinotropic polypeptide) is the other major incretin receptor. The glucagon receptor participates in hepatic glucose and energy-expenditure signaling. These are mechanistic descriptions of receptor biology, not statements about treating any condition.
Single-receptor agonism
A single agonist activates one of these receptors. Semaglutide, for example, is discussed as a GLP-1 receptor agonist. Single-target compounds are the simplest to reason about mechanistically because their pharmacology centers on one receptor's signaling, though downstream physiology is still complex.
Dual and triple agonism
Some peptides engage more than one receptor. Tirzepatide is described as a dual GIP and GLP-1 receptor agonist, and retatrutide is discussed as a triple agonist engaging GIP, GLP-1, and glucagon receptors. The rationale studied in the literature is that co-activating complementary receptors produces a different combined signaling profile than any single target alone.
Why the classification matters
Framing these compounds by receptor class—single, dual, or triple—is more accurate than ranking them by outcome, and it avoids overstated claims. Approval status varies by compound and jurisdiction; several triple agonists remain investigational and are not authorized by Health Canada. This is an educational overview of receptor pharmacology, not medical advice.
The incretin & metabolic co-agonist class at a glance
| Peptide | Receptors | Length | Mass (Da) | Half-life | Status |
|---|---|---|---|---|---|
| GLP-1 | GLP-1R | 30 aa | ≈ 3,297.6 | ≈ 1–2 min (DPP-4 cleavage + renal clearance) | Endogenous hormone — not a product |
| Liraglutide | GLP-1R | 31 aa | ≈ 3,751.2 | ≈ 13 h (once-daily dosing) | Approved: Victoza (2010, T2D), Saxenda (2014, weight) |
| Semaglutide | GLP-1R | 31 aa | ≈ 4,113.6 | ≈ 7 days (≈ 145–165 h in clinical PK studies) | Approved: Ozempic (2017, T2D), Rybelsus (2019, oral T2D), Wegovy (2021, weight) |
| Tirzepatide | GIPR + GLP-1R | 39 aa | ≈ 4,813.5 | ≈ 5 days (≈ 117 h) | Approved: Mounjaro (2022, T2D), Zepbound (2023, weight; 2024, obstructive sleep apnoea) |
| Retatrutide | GIPR + GLP-1R + GCGR | 39 aa | ≈ 4,731 | ≈ 6 days | Investigational (phase 3) |
| Cagrilintide | Amylin / calcitonin | 37 aa | ≈ 4,409 | ≈ 7–8 days (159–195 h across doses in the phase 1b study) | Investigational (phase 3, as CagriSema with semaglutide) |
| Survodutide | GCGR + GLP-1R | 29 aa | ≈ 4,232 | Supports once-weekly dosing (published population estimates are on the order of several days) | Investigational (phase 3: SYNCHRONIZE obesity programme; MASH programme) |
| Mazdutide | GCGR + GLP-1R | 34 aa | ≈ 4,476 | Supports once-weekly dosing (published estimates are on the order of several days) | Approved in China (NMPA): chronic weight management (27 June 2025) and type 2 diabetes (2025) |
| Amycretin | GLP-1R + amylin | — | — | Supports once-weekly subcutaneous dosing | Investigational (phase 2 results published 2025; later-phase trials under way) |
Verified from PubChem, IUPHAR and the primary discovery papers cited on each profile. Half-lives are approximate population means from published pharmacokinetics.
Sources and what they cover
These primary studies, official records and standards cover the topics linked below. The scope notes distinguish laboratory findings, human trials and regulatory records. This is a selected bibliography, not a systematic review or verification of every sentence; absence of a study here does not prove that no study exists.
- Willard et al. (2020) — Tirzepatide as an imbalanced, biased dual receptor agonist
Primary receptor pharmacology and molecular design; not itself a clinical outcomes trial.
Relevant sections: Single-receptor agonism · Dual and triple agonism
- Li et al. (2024) — Structural basis of retatrutide triple-receptor agonism
Structural receptor research; biological plausibility is separate from proven clinical benefit.
Relevant sections: Three receptors, one metabolic system · What each receptor does · Dual and triple agonism · Why the classification matters
FAQ
What is the difference between GLP-1, GIP, and glucagon?+
They are three different peptide hormones acting on three different receptors within the metabolic system. GLP-1 and GIP are gut-derived incretins; glucagon is pancreatic. Modern metabolic peptides are classified by which of these receptors they activate.
What is a dual or triple agonist?+
A dual agonist activates two of these receptors (for example GIP and GLP-1), and a triple agonist activates three (GIP, GLP-1, and glucagon). The mechanistic idea studied in the literature is co-activating complementary receptor pathways.
Are triple agonists approved?+
It varies by compound and jurisdiction. Several triple-agonist peptides remain investigational and are not authorized by Health Canada. This overview describes receptor mechanisms and approval status, not treatment recommendations.