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What Is GLP-1?
GLP-1 (glucagon-like peptide-1) is an incretin hormone produced and secreted by intestinal L-cells in the small intestine and colon, triggered by food intake. It plays a central role in regulating blood glucose and appetite through three primary mechanisms: it stimulates the pancreas to release insulin in a glucose-dependent manner, suppresses glucagon secretion from alpha cells, and slows gastric emptying — all of which together blunt post-meal blood sugar spikes.
Native GLP-1 has a plasma half-life of roughly 1–2 minutes, degraded almost immediately by the enzyme dipeptidyl peptidase-4 (DPP-4). This rapid clearance is why pharmaceutical GLP-1 receptor agonists are engineered to resist DPP-4 and last hours to weeks.
GLP-1 also acts on the central nervous system — specifically the hypothalamus and brainstem — to reduce appetite and food intake. This central effect is what drives the significant weight-loss seen in clinical trials of GLP-1 receptor agonist drugs.[1]
How GLP-1 Receptor Agonists Work
GLP-1 receptor agonists (GLP-1 RAs) are compounds — all peptides — that bind to and activate the GLP-1 receptor (GLP1R), a G-protein-coupled receptor found in pancreatic beta cells, the brain, heart, kidney, and gut. Activation triggers a cyclic AMP cascade that amplifies insulin secretion only when blood glucose is elevated, which is why GLP-1 RAs have a low intrinsic risk of hypoglycaemia compared with sulfonylureas.
The core pharmacological modifications used to extend half-life include: fatty acid chains that bind serum albumin (semaglutide, liraglutide), amino-acid substitutions that block DPP-4 cleavage, and in the case of tirzepatide, a dual-agonist design targeting both GLP-1 and GIP receptors simultaneously.
The Main GLP-1 Drugs and Medications
All approved GLP-1 medications are peptide-based drugs. Here is how the major ones compare:
| Compound | Brand Name(s) | Receptor Target | Half-Life | Dosing |
|---|---|---|---|---|
| Semaglutide | Ozempic (T2D), Wegovy (obesity), Rybelsus (oral) | GLP-1 | ~7 days | Weekly injection or daily oral |
| Liraglutide | Victoza (T2D), Saxenda (obesity) | GLP-1 | ~13 hours | Daily injection |
| Tirzepatide | Mounjaro (T2D), Zepbound (obesity) | GLP-1 + GIP | ~5 days | Weekly injection |
| Retatrutide | N/A (Phase III trials) | GLP-1 + GIP + Glucagon | ~6 days | Weekly injection |
| Exenatide | Byetta, Bydureon | GLP-1 | 2.4 h / 2 weeks | Twice daily or weekly |
| Cagrilintide | N/A (Phase III, co-dosed with sema) | Amylin receptor | ~7 days | Weekly injection |
Note: Cagrilintide targets the amylin receptor, not GLP-1R, but is often grouped with GLP-1 class drugs in research contexts because it is co-administered with semaglutide (CagriSema). It is structurally a peptide.
Are GLP-1 Drugs Peptides? Yes — Here Is Why
A peptide is any chain of amino acids linked by peptide bonds. There is no single agreed cutoff between a “peptide” and a “protein” in pharmacology — conventions typically place the dividing line at roughly 50–100 amino acids, though this varies by context. The key point: almost every GLP-1 medication is a short amino-acid chain, which places it unambiguously in the peptide category.
- Semaglutide — 31 amino acids; 94% sequence homology with native GLP-1; modified at positions 8 and 34 and conjugated to a fatty di-acid via a linker for albumin binding.[2]
- Tirzepatide — 39 amino acids; dual GLP-1/GIP agonist; C18 fatty di-acid attached to lysine at position 20.[3]
- Liraglutide — 34 amino acids; 97% homology with GLP-1; palmitoyl fatty acid at position 26.
- Exenatide — 39 amino acids; derived from exendin-4, a peptide found in Gila monster venom; 53% homology with GLP-1.
- Retatrutide — 39 amino acids; triple agonist design at GLP-1, GIP, and glucagon receptors.
So yes — Ozempic, Mounjaro, Wegovy, and the rest are all peptide drugs. The word “peptide” describes their molecular class. That they are prescription medications regulated by Health Canada (or the FDA) is a separate fact about their regulatory status, not their chemistry.
Insulin is also a peptide. So are vasopressin, oxytocin, calcitonin, and hundreds of other approved medicines. Calling them “peptides” is not a regulatory or legal category — it is a chemistry category.
Single, Dual, and Triple Agonists — How GLP-1 Peptides Compare
Research in metabolic peptides has progressed from GLP-1-only compounds toward multi-receptor agonists. Here is the current classification:
Single Agonists — GLP-1 Only
Semaglutide, liraglutide, and exenatide target GLP-1R exclusively. These are the most studied compounds with the longest regulatory track record. Semaglutide at 2.4 mg weekly (Wegovy dose) produced mean weight loss of ~15% at 68 weeks in the STEP-1 trial (N=1,961).[4]
Dual Agonists — GLP-1 + GIP
Tirzepatide co-activates both GLP-1R and the glucose-dependent insulinotropic polypeptide receptor (GIPR). The SURMOUNT-1 trial (N=2,539) showed mean weight loss of 20.9% at the 15 mg dose over 72 weeks — meaningfully greater than semaglutide monotherapy.[5] The mechanism behind the additional GIPR activity’s contribution to weight loss is still under investigation.
Triple Agonists — GLP-1 + GIP + Glucagon
Retatrutide adds glucagon receptor (GCGR) agonism to the dual GLP-1/GIP profile. Phase II data (N=338, 48 weeks) showed up to 24.2% body weight reduction at the highest dose — the most in any randomized trial at that time.[6] Glucagon receptor activation increases energy expenditure, which may explain the enhanced effect beyond dual agonism. Phase III trials are ongoing as of 2026.
Amylin Analogues — Cagrilintide
Cagrilintide is an amylin analogue, not a GLP-1 drug. Amylin (IAPP) is co-secreted with insulin from pancreatic beta cells and acts on area postrema receptors to reduce food intake and slow gastric emptying. Cagrilintide is being developed in combination with semaglutide (CagriSema) and showed 15.6% weight reduction at 32 weeks in Phase II.[7]
Regulatory vs Chemistry — The Distinction That Matters
In Canada, semaglutide and tirzepatide are regulated under the Food and Drugs Act as prescription drugs (NOC issued by Health Canada). They can only be legally dispensed with a physician prescription — their peptide chemistry does not change this. Research peptide suppliers in Canada may sell semaglutide or tirzepatide as research chemicals that are explicitly “not for human use.”
The chemistry category (peptide) and the regulatory category (prescription drug / research chemical) are independent of one another. A compound can be both a peptide and a prescription drug. Understanding this distinction is essential for anyone comparing products across different procurement contexts.
Handling and Purity Standards for Metabolic Research Peptides
GLP-1 class peptides used in research settings require specific handling:
- Reconstitution: Lyophilized peptide powder is reconstituted with bacteriostatic water (BAC water, 0.9% benzyl alcohol). Sterile water without benzyl alcohol is suitable only for immediate single-use.
- Storage: Lyophilized powder is stable at room temperature; reconstituted solution should be stored at 2–8°C and used within 28 days typically.
- Purity: A minimum of ≥98% HPLC purity is standard for research-grade GLP-1 peptides. Third-party certificate of analysis (CoA) with mass spec confirmation is the quality benchmark.
- Cagrilintide-specific handling: Cagrilintide solution is highly prone to gelation and opalescence at room temperature due to its amylin-analogue properties — this is expected and reversible with gentle re-chilling; see dedicated handling guide for details.
Frequently Asked Questions
What is GLP-1?
GLP-1 (glucagon-like peptide-1) is an incretin hormone produced in the intestine that stimulates insulin release, suppresses glucagon, slows gastric emptying, and reduces appetite. It is released in response to food and is degraded within 1–2 minutes by the DPP-4 enzyme. GLP-1 receptor agonist drugs mimic its effects with extended half-lives.
What is a GLP-1 receptor agonist?
A GLP-1 receptor agonist is a compound that binds to and activates the GLP-1 receptor (GLP1R). All approved GLP-1 receptor agonists (semaglutide, tirzepatide, liraglutide, exenatide, dulaglutide) are peptides modified to resist rapid enzymatic degradation, extending their action from minutes to days or weeks.
Is semaglutide a peptide?
Yes. Semaglutide is a 31-amino-acid peptide with 94% sequence homology to native GLP-1. It has two structural modifications: an amino acid substitution at position 8 (alanine → α-amino-isobutyric acid) to resist DPP-4, and a fatty di-acid chain attached via a linker at lysine 34 to enable albumin binding and extend half-life to approximately 7 days.
Is tirzepatide a peptide?
Yes. Tirzepatide is a 39-amino-acid dual agonist peptide that activates both GLP-1 and GIP receptors. It is structurally a GIP/GLP-1 co-agonist based on the GIP sequence scaffold, with a C18 fatty di-acid attached at position 20 for extended half-life (~5 days).
Are GLP-1 drugs the same as research peptides?
The same molecules (semaglutide, tirzepatide) can be found in approved prescription drugs and as research-grade peptides from research chemical suppliers. The chemistry is the same; the regulatory status differs. Prescription versions (Ozempic, Mounjaro) are approved for specific indications and formulated to pharmaceutical standards. Research peptides are sold explicitly for non-human research purposes and have not been subject to the clinical approval process for those specific formulations.
What is the difference between semaglutide, tirzepatide, and retatrutide?
The key difference is receptor targeting: semaglutide activates GLP-1 receptors only; tirzepatide co-activates GLP-1 and GIP receptors; retatrutide co-activates GLP-1, GIP, and glucagon receptors. Each additional receptor target appears to produce greater weight loss in trials, with retatrutide showing ~24% mean weight loss in Phase II — the highest reported figure in a controlled trial as of 2025.
References
- Baggio LL, Drucker DJ. Biology of incretins: GLP-1 and GIP. Gastroenterology. 2007;132(6):2131–2157. PMID 17498508
- Lau J, et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. J Med Chem. 2015;58(18):7370–7380. PMID 26308095
- Coskun T, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus. Mol Metab. 2018;18:3–14. PMID 30473097
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989–1002. PMID 33567185
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216. PMID 35658024
- Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity — a Phase 2 trial. N Engl J Med. 2023;389(6):514–526. PMID 37385013
- Enebo LB, et al. Safety, tolerability, pharmacokinetics, and pharmacodynamics of cagrilintide with semaglutide 2.4 mg for weight management. Lancet. 2021;397(10286):1736–1748. PMID 34348213
Related Research Articles
Explore our complete GLP-1 receptor agonist research library: Semaglutide vs Tirzepatide vs Retatrutide in Canada, Retatrutide Reconstitution Guide, and Ipamorelin Half-Life and Onset Data.
