The GLP-1 Class: Semaglutide, Tirzepatide, and Retatrutide Research
Class research profile
The GLP-1 Class — Semaglutide, Tirzepatide, and Retatrutide
Three generations of incretin-based research peptides. Single, dual, and triple receptor agonists. Compared head-to-head on mechanism, peer-reviewed outcomes, and analytical purity. HPLC-verified, COAs on every lot.
TL;DR. The GLP-1 class includes Semaglutide, Tirzepatide, and Retatrutide, each studied in peer-reviewed GLP-1, GIP, and glucagon receptor research. Improved Peptides supplies these compounds for in vitro and laboratory research only — not for human consumption — with third-party COAs.
What is the GLP-1 class?
The GLP-1 class is a family of synthetic peptide research compounds that act as agonists at the glucagon-like peptide-1 (GLP-1) receptor. The class has expanded across three generations, each broadening the receptor scope:
| Generation | Compound | Receptor scope | Year of first synthesis |
|---|---|---|---|
| 1st | Semaglutide | GLP-1 receptor (single) | 2012 |
| 2nd | Tirzepatide | GLP-1 + GIP (dual) | 2018 |
| 3rd | Retatrutide | GLP-1 + GIP + Glucagon (triple) | 2022 |
Each compound has been studied in peer-reviewed Phase 2 and Phase 3 trials for metabolic and incretin-pathway research. Improved Peptides supplies all three for in vitro and laboratory research only — not for human consumption.
Side-by-side comparison
| Dimension | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Class | GLP-1 single agonist | GLP-1/GIP dual agonist | GLP-1/GIP/Glucagon triple agonist |
| Half-life | ~165 hours (~7 days) | ~120 hours (~5 days) | ~150 hours (~6 days) |
| Mechanism scope | GLP-1 only | GLP-1 + GIP | GLP-1 + GIP + Glucagon |
| Phase status (2026) | Approved (Wegovy/Ozempic in clinical settings) | Approved (Mounjaro/Zepbound in clinical settings) | Phase 3 ongoing |
| Notable Phase 2 outcome | STEP/SELECT/SUSTAIN trial program | SURPASS/SURMOUNT trial program | Phase 2 body-composition outcomes published in 2023 (Jastreboff et al., NEJM) |
| Research interest trend | Plateau — well-characterized | Rising — extensive recent literature | Steep rise — newest, most actively studied |
| Improved Peptides purity | HPLC 99%+ | HPLC 99%+ | HPLC 99%+ |
| Product page | Shop Semaglutide | Shop Tirzepatide | Shop Retatrutide |
| Research profile | Semaglutide research | Tirzepatide research | Retatrutide research |
Mechanism deep dive
Semaglutide — GLP-1 single agonism
Semaglutide is a long-acting analog of human GLP-1 with a fatty-acid side chain that extends its plasma half-life via albumin binding. It binds selectively to the GLP-1 receptor, modulating glucose-dependent insulin secretion, gastric emptying, and central appetite signaling pathways studied in incretin research.
Tirzepatide — GLP-1 + GIP dual agonism
Tirzepatide is a 39-amino-acid synthetic peptide engineered to activate both the GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. The dual-agonist design has been studied for additive effects on insulin sensitivity, lipolysis, and energy expenditure beyond GLP-1 monotherapy.
Retatrutide — GLP-1 + GIP + Glucagon triple agonism
Retatrutide is the third-generation tri-agonist, adding glucagon receptor activity to the GLP-1/GIP combination. Glucagon-receptor signaling has been studied for its role in hepatic energy metabolism and basal metabolic rate. Phase 2 data (Jastreboff et al., 2023) reported the largest body-composition changes observed across the class.
Citations (peer-reviewed, PubMed-linked)
Semaglutide
- Marso SP, et al. “Semaglutide and Cardiovascular Outcomes (SUSTAIN-6).” NEJM. 2016. PMID: 27633186
- Wilding JPH, et al. “Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1).” NEJM. 2021. PMID: 33567185
- Davies M, et al. “Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2).” Lancet. 2021. PMID: 33667417
- Lincoff AM, et al. “Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT).” NEJM. 2023. PMID: 37952131
Tirzepatide
- Frias JP, et al. “Tirzepatide versus Semaglutide Once Weekly (SURPASS-2).” NEJM. 2021. PMID: 34170647
- Jastreboff AM, et al. “Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1).” NEJM. 2022. PMID: 35658024
- Rosenstock J, et al. “Efficacy and safety of tirzepatide monotherapy (SURPASS-1).” Lancet. 2021. PMID: 34186022
- Karagiannis T, et al. “Tirzepatide vs other GLP-1 RAs: systematic review and meta-analysis.” BMJ. 2022. PMID: 35338814
Retatrutide
- Jastreboff AM, et al. “Triple-Hormone-Receptor Agonist Retatrutide for Obesity — Phase 2.” NEJM. 2023. PMID: 37354450
- Rosenstock J, et al. “Retatrutide, a GIP/GLP-1/glucagon receptor agonist, in adults with type 2 diabetes.” Lancet. 2023. PMID: 37356449
- Sanyal AJ, et al. “Retatrutide for metabolic dysfunction-associated steatotic liver disease.” Lancet GH. 2024. PMID: 38663433
Quality and verification
Every batch of Semaglutide, Tirzepatide, and Retatrutide is independently tested by a third-party laboratory using:
- HPLC — for purity (target 99%+)
- Mass spectrometry — for sequence confirmation
- UV spectroscopy — for concentration verification
Current batch COAs are published in our COA Library and linked from each product page. Every lot is traceable.
Storage and reconstitution (research reference)
| Stage | Condition |
|---|---|
| Lyophilized vial (shipping) | Room temperature, stable for 2-3 weeks |
| Lyophilized vial (long-term) | Refrigerator (2-8°C) for 6-12 months; freezer (-20°C) for 24+ months |
| Reconstituted (with bacteriostatic water) | Refrigerated, use within 28 days |
Reconstitution solvent: Bacteriostatic water with 0.9% benzyl alcohol. Available at /shop/bacteriostatic-water/.
Choosing between the three (research framework)
Researchers selecting between Semaglutide, Tirzepatide, and Retatrutide typically evaluate four axes:
- Mechanism scope: Single (Sema) → Dual (Tirz) → Triple (Reta) receptor activation
- Published outcome magnitude: Phase 2 body-composition data trends Reta > Tirz > Sema
- Research history: Sema has the longest published record; Reta has the newest
- Cost-per-mg: Sema lowest, Reta highest at current market rates
The choice depends on the research question being investigated. All three are stocked, HPLC-verified, and ship same-day on orders before 2pm ET.
FAQ
Q: What is the GLP-1 class?
A: A family of synthetic peptide research compounds that activate the GLP-1 receptor. The class has expanded to include dual (GLP-1/GIP) and triple (GLP-1/GIP/Glucagon) receptor agonists.
Q: What is the difference between Semaglutide, Tirzepatide, and Retatrutide?
A: Semaglutide is a single GLP-1 agonist. Tirzepatide is a dual GLP-1 + GIP agonist. Retatrutide is a triple GLP-1 + GIP + Glucagon agonist. They differ in receptor scope, half-life, and the breadth of peer-reviewed published research.
Q: Where do I find peer-reviewed citations?
A: Citations for all three compounds are listed in the section above with direct PubMed links. We update the citation list as new peer-reviewed research is published.
Q: What purity standard does Improved Peptides verify?
A: HPLC-tested 99%+ purity, sequence-confirmed by mass spectrometry, with a COA from an independent third-party lab on every batch.
Q: Are these peptides legal to purchase?
A: All compounds offered by Improved Peptides are sold strictly for in vitro and laboratory research use. They are not for human consumption, diagnosis, or treatment.
Q: Which GLP-1 compound has the most published research?
A: Semaglutide currently has the longest and most extensive published record, with Tirzepatide rapidly expanding. Retatrutide is the newest and has the most active research pipeline.
Q: How is the Wolverine Stack different from the GLP-1 class?
A: The Wolverine Stack is a tissue-repair research combination (BPC-157 + TB-500). The GLP-1 class is a metabolic/incretin research family. Different mechanisms, different research applications.
Ready to source the GLP-1 class?
All three compounds — Semaglutide, Tirzepatide, and Retatrutide — are stocked, HPLC-tested, and ship same-day on orders before 2pm ET.
Shop Semaglutide | Shop Tirzepatide | Shop Retatrutide | View All Class Components