What is the main difference between Retatrutide, Tirzepatide and Semaglutide?

The number of receptors each one activates. Semaglutide is a single GLP-1 agonist. Tirzepatide is a dual agonist acting on both GIP and GLP-1. Retatrutide is a triple agonist adding glucagon to those two. Each addition changes the mechanism being studied rather than simply increasing potency.

Is a triple agonist better than a dual or single agonist?

Not automatically. More receptors means a broader mechanism, not a strictly superior one, and it also means more variables in any study. The three also differ sharply in how well established they are: Semaglutide and Tirzepatide have regulatory approval and large trial programmes behind them, while Retatrutide remains investigational.

Why does Retatrutide include glucagon when glucagon raises blood sugar?

Because glucagon receptor activation also increases energy expenditure and influences how the liver handles fat. The research interest is in combining reduced intake, via GLP-1 and GIP, with increased expenditure, via glucagon — an approach neither of the other two compounds allows.

How does Cagrilintide fit alongside these three?

It does not belong to this family. Cagrilintide is an amylin analogue acting on an entirely separate receptor system, which is why it is studied in combination with Semaglutide rather than as a competitor to it. Our Cagrilintide guide covers that mechanism in full.

Are any of these approved for use in Australia?

These are research-grade compounds and are not approved by the TGA for human or veterinary use. Regulatory approvals held elsewhere apply to specific pharmaceutical products, not to research compounds, and nothing in this guide is medical advice or a therapeutic claim.

Research Library›Comparisons›Retatrutide vs Tirzepatide vs Semaglutide

Metabolic Comparison

Retatrutide vs Tirzepatide vs Semaglutide: How the Three Generations Differ

One receptor, two, or three. The incretin compounds are usually discussed as if they were versions of the same thing — but each acts on a different combination of receptors, and that is what separates them.

9 min read·6 studies cited·Updated July 2026

Quick Reference

Semaglutide	GLP-1 only (single agonist)
Tirzepatide	GIP + GLP-1 (dual agonist)
Retatrutide	GIP + GLP-1 + glucagon (triple agonist)
Shared route	All three are once-weekly in published trials
Status	Research use only — not TGA approved

The Short Answer

These three compounds are best understood as successive generations of the same idea, each adding a receptor. Semaglutide activates one receptor (GLP-1). Tirzepatide activates two (GIP and GLP-1). Retatrutide activates three (GIP, GLP-1 and glucagon).

More receptors is not automatically "better" — each addition changes what the compound does and what the research questions become. The useful comparison is not which is strongest, but which mechanism a given piece of research is actually interested in.

	Semaglutide	Tirzepatide	Retatrutide
Receptors	GLP-1	GIP + GLP-1	GIP + GLP-1 + glucagon
Class	Single agonist	Dual agonist	Triple agonist
Developer	Novo Nordisk	Eli Lilly	Eli Lilly
Trial dosing	Once weekly	Once weekly	Once weekly
Regulatory status	Approved (US/EU) for diabetes and weight	Approved (US) 2022 diabetes, 2023 weight	Investigational — Phase 3 ongoing
Distinguishing feature	The reference GLP-1 compound	Added GIP alongside GLP-1	Adds glucagon — energy expenditure, not just intake

What Each Receptor Actually Does

The differences only make sense once the three receptors are separated out. Each is a distinct signalling system that happens to converge on metabolic regulation.

The three receptors, in plain language: think of the body’s energy balance as a household budget. GLP-1 is the voice at the table saying “we have spent enough today” — it arrives after a meal and signals fullness. GIP is the accountant deciding where the money actually goes: what gets stored as fat, what gets burned now. Glucagon is the opposite impulse — the one that opens the savings account and spends, releasing stored energy instead of tucking more away. Semaglutide brings only the first voice. Tirzepatide brings the voice and the accountant. Retatrutide brings all three, which is why it is the only one of them studied for influencing what goes out rather than only what comes in.

GLP-1 (glucagon-like peptide-1) is an incretin hormone released from the gut after eating. It stimulates glucose-dependent insulin secretion, slows gastric emptying, and acts on appetite centres in the brain. This is the mechanism every compound here shares.

GIP (glucose-dependent insulinotropic polypeptide) is the other major incretin. It also enhances insulin secretion, but additionally acts on adipose tissue and appears to influence how fat is stored and used. Adding GIP to GLP-1 is what defines Tirzepatide.

Glucagon is the counter-regulatory partner to insulin, and its inclusion is initially counterintuitive — it raises blood glucose. But glucagon receptor activation also increases energy expenditure and influences hepatic fat metabolism. Retatrutide’s triple mechanism is studied for combining reduced intake (GLP-1/GIP) with increased expenditure (glucagon).

Why the third receptor changes the question: semaglutide and Tirzepatide are both studied primarily through the lens of intake — appetite signalling, satiety, gastric emptying. Retatrutide adds an expenditure arm.

That makes it a different kind of research tool rather than simply a stronger one: studies can examine what happens when intake and expenditure are acted on at the same time, which neither of the other two allows.

Where the Evidence Stands

The three sit at very different points on the evidence curve, and this is the single most important practical distinction between them.

Semaglutide has the longest and deepest record — approved for type 2 diabetes and later for weight management, with large cardiovascular outcome data behind it. It is the reference compound the others are measured against.

Tirzepatide followed, with FDA approval in 2022 for type 2 diabetes and 2023 for weight management, supported by the SURPASS and SURMOUNT trial programmes. Head-to-head trial data against semaglutide exists, which is unusual and makes the comparison unusually well grounded.

Retatrutide is the newest and least settled. Eli Lilly’s Phase 2 results, published in 2023, drew considerable attention, and Phase 3 work is ongoing. It has no regulatory approval anywhere. Any claim about how it compares long-term is, at this stage, an extrapolation from early data.

The asymmetry worth remembering: it is easy to read the three as a simple ranking — one receptor, two, three — and assume the newest is the best-established. The opposite is true: the compound with the most receptors has the least long-term human data behind it.

Semaglutide has years of post-approval evidence; Retatrutide has promising early-phase results and open questions. Both facts matter when weighing which compound a study should use.

Frequently Asked Questions

Compiled by the Southern Pacific Labs research team. Last updated July 2026.

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Published References

Jastreboff AM, Kaplan LM, Frías JP, et al. “Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial.” The New England journal of medicine, 2023. PubMed
Jastreboff AM, Aronne LJ, Ahmad NN, et al. “Tirzepatide Once Weekly for the Treatment of Obesity.” The New England journal of medicine, 2022. PubMed
Frías JP, Davies MJ, Rosenstock J, et al. “Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes.” The New England journal of medicine, 2021. PubMed
Wilding JPH, Batterham RL, Calanna S, et al. “Once-Weekly Semaglutide in Adults with Overweight or Obesity.” The New England journal of medicine, 2021. PubMed
Marso SP, Bain SC, Consoli A, et al. “Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes.” The New England journal of medicine, 2016. PubMed
Samms RJ, Coghlan MP, Sloop KW. “How May GIP Enhance the Therapeutic Efficacy of GLP-1?” Trends in endocrinology and metabolism: TEM, 2020. PubMed