GLP-1 Peptides Compared: Semaglutide, Tirzepatide & Retatrutide

GLP-1 peptides are a class of synthetic incretin-mimetic molecules that activate the glucagon-like peptide-1 (GLP-1) receptor, and in newer designs additional metabolic receptors such as GIP, glucagon and the amylin receptor. As a research subject, these peptides are studied for their role in glucose-dependent insulin secretion, gastric emptying, appetite-regulating neural circuits and energy balance. This article compares four widely discussed peptides in the class — semaglutide, tirzepatide, retatrutide and cagrilintide — by their receptor targets and the published trial context that has driven scientific interest. It is written for an educational, laboratory-research audience.

For research use only — not for human or veterinary use. The peptides discussed here are supplied by TXLABS as research-grade reference material for in-vitro and laboratory work. Where approved medicines are mentioned, they are described only to provide scientific context; nothing below is medical, dosing or treatment advice.

What are GLP-1 and incretin peptides?

Incretins are gut-derived peptide hormones released after nutrient intake. The two principal human incretins are glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). In published mechanistic reviews, GLP-1 receptor activation is associated with glucose-dependent insulin secretion, slowed gastric emptying and signalling in central and peripheral nervous-system pathways that regulate satiety and food intake. GIP is another incretin whose receptor is expressed in the pancreas, adipose tissue and brain regions involved in energy balance.

The term “GLP-1 peptide” is often used loosely to cover a broader family of incretin peptides and related metabolic agonists. Some target a single receptor; others are engineered as dual or triple receptor agonists that combine GLP-1 activity with GIP, glucagon or amylin signalling. Understanding which receptors a given molecule engages is the starting point for any comparison.

How do receptor agonists work at the mechanism level?

A receptor agonist is a molecule that binds and activates a specific receptor, reproducing or amplifying the downstream signalling of the native hormone. Preclinical literature describes each target differently:

• GLP-1 receptor: associated with glucose-dependent insulin release, reduced gut motility and satiety signalling in the central nervous system.
• GIP receptor: a second incretin pathway; research in animal models suggests central GIP signalling contributes to appetite regulation, and that combined GIP/GLP-1 agonism can inhibit hunger-promoting AgRP neurons more potently than either pathway alone.
• Glucagon receptor: studied for its influence on energy expenditure and hepatic lipid metabolism, adding a distinct axis to the incretin effects.
• Amylin receptor: amylin is a pancreatic hormone co-secreted with insulin; amylin-receptor agonists are researched for their effects on satiety and gastric emptying through a pathway separate from the incretins.

How do semaglutide, tirzepatide, retatrutide and cagrilintide compare?

The clearest way to distinguish these peptides is by the receptors each one engages. The published clinical context below refers to trials of the corresponding approved or investigational medicines; TXLABS supplies the research-grade reference material only.

• Semaglutide — single GLP-1 receptor agonist. The most extensively characterised molecule in the class. In the 2023 SELECT cardiovascular-outcomes trial (17,604 participants), the approved medicine was associated with a lower rate of major adverse cardiovascular events versus placebo, and STEP-programme trials reported substantial body-weight reductions. Semaglutide is frequently used as the scientific benchmark against which newer agonists are compared.
• Tirzepatide — dual GIP/GLP-1 receptor agonist. By activating both incretin receptors, tirzepatide is studied as a step beyond single-pathway agonism. In the SURPASS-2 trial in type 2 diabetes it was compared directly with semaglutide, and the 72-week SURMOUNT-5 trial reported greater weight reduction for tirzepatide than semaglutide in adults with obesity or overweight and related conditions — the central data point in the tirzepatide vs semaglutide research conversation.
• Retatrutide — triple GIP/GLP-1/glucagon receptor agonist. This triple agonist peptide adds glucagon-receptor activity to the dual incretin design. A 2023 Phase 2 trial published in the New England Journal of Medicine reported a mean body-weight reduction of roughly 24% at the highest dose over 48 weeks, alongside a separate Phase 2 study in type 2 diabetes and a Phase 2a study in metabolic-associated steatotic liver disease. As an earlier-stage investigational molecule, retatrutide is a frequent focus of the retatrutide vs tirzepatide comparison.
• Cagrilintide — long-acting amylin-receptor agonist. Cagrilintide sits outside the incretin family, working through the amylin pathway. It is most studied in combination with semaglutide (as CagriSema): in the REDEFINE 1 Phase 3 trial, the combination reported greater weight reduction than either cagrilintide or semaglutide alone, illustrating research interest in pairing an amylin agonist with a GLP-1 agonist.

What does the research interest in each peptide focus on?

Across the peer-reviewed literature, interest tends to cluster around a few questions. For semaglutide, the emphasis is on long-term cardiovascular and metabolic endpoints and its role as a reference compound. For tirzepatide, the question is whether dual incretin agonism confers measurable advantages over GLP-1 alone. For retatrutide, researchers examine whether adding glucagon-receptor activity changes energy expenditure and hepatic outcomes. For cagrilintide, the focus is on amylin biology and combination approaches. These are active, evolving areas — several of these molecules remain investigational and not approved in Australia, the US or the EU.

What does “research reference material” mean here?

When TXLABS describes a peptide as research reference material, it means a characterised, research-grade compound intended solely for laboratory investigation — for example, in-vitro assays, analytical method development, receptor-binding studies and comparative research. It is not a medicine, a supplement or a therapeutic product, and it is not manufactured, packaged or supplied for administration to humans or animals.

This distinction matters. The clinical trials referenced above studied approved or investigational pharmaceutical products under regulated conditions. The research-grade material supplied for laboratory use is a separate category: reference-standard compounds that let researchers study the underlying biochemistry. Conflating the two would be inaccurate.

Research-grade reference material is intended for controlled laboratory use by qualified researchers. It is not a substitute for an approved medicine and carries no therapeutic claims.

How should researchers approach this peptide class?

For laboratories comparing molecules in this class, the receptor-target framework is the most useful organising principle: single-agonist (semaglutide), dual-agonist (tirzepatide), triple-agonist (retatrutide) and amylin-pathway (cagrilintide). Each represents a different hypothesis about how combining metabolic signalling pathways affects downstream measures. Sourcing well-characterised reference material with clear identity and purity documentation supports reproducible work.

You can review the individual research-grade compounds discussed here on the TXLABS product pages: semaglutide, tirzepatide, retatrutide and cagrilintide. The full catalogue of research reference material is available in the TXLABS shop.

Summary

The GLP-1/incretin peptide class spans single-receptor agonists through to triple agonists and amylin-pathway compounds. Semaglutide activates GLP-1; tirzepatide adds GIP; retatrutide adds glucagon; and cagrilintide works through amylin. The published trial context explains why each has become a focus of metabolic research, while the distinction between approved medicines and research-grade reference material remains fundamental. TXLABS supplies these peptides strictly as reference material.

For research use only — not for human or veterinary use. This content is educational and does not constitute medical advice.