In brief: semaglutide targets the GLP-1 receptor, tirzepatide targets GIP and GLP-1 receptors, and retatrutide targets GIP, GLP-1 and glucagon receptors. That single–dual–triple distinction is useful, but it does not by itself show which molecule is “best”. The evidence comes from separate research programmes with different populations, durations, protocols and regulatory status.
Semaglutide, tirzepatide and retatrutide are often placed side by side because all three appear in metabolic research. Yet they are not interchangeable molecules, and a responsible comparison needs to go beyond headline percentages.
This guide compares their receptor profiles, landmark obesity studies and present level of evidence. It is an educational research overview—not medical advice, a dosing guide or a recommendation for human use.
The quick comparison
| Feature | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Receptor profile | GLP-1 | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Common scientific description | Single receptor agonist | Dual receptor agonist | Triple receptor agonist |
| Landmark obesity study | STEP 1 | SURMOUNT-1 | Phase 2 obesity trial |
| Research maturity | Established clinical evidence; authorised prescription uses | Established clinical evidence; authorised prescription uses | Investigational; Phase 3 development |
Regulatory status depends on the product, indication and country. Retatrutide remains investigational and is not approved by any regulatory agency, according to its developer.
The shared biological context
All three molecules engage receptor systems involved in metabolic signalling, but each has a different design:
- GLP-1 is associated with glucose-dependent insulin signalling, glucagon regulation, gastric emptying and appetite-related pathways.
- GIP is another incretin pathway involved in glucose-dependent insulin secretion and wider metabolic signalling.
- Glucagon has roles in hepatic glucose output and energy metabolism. Combining glucagon receptor activity with incretin activity is scientifically interesting, but it also requires careful balancing and clinical evaluation.
“Agonist” means a molecule activates a receptor. It does not mean every receptor is activated with equal strength, for the same duration or with the same downstream effect. Receptor count is therefore a starting point—not a complete description of pharmacology.
Semaglutide: a GLP-1 receptor research profile
Semaglutide is a GLP-1 receptor agonist. Of the three molecules compared here, it has the simplest receptor profile: one principal receptor target. “Single” does not mean weak or basic; it means the molecule’s primary pharmacological classification centres on GLP-1 receptor activity.
A landmark obesity study was STEP 1, published in 2021. It enrolled 1,961 adults with overweight or obesity and ran for 68 weeks. The mean change in body weight was −14.9% in the semaglutide group and −2.4% with placebo, alongside lifestyle intervention.
That result is important evidence for semaglutide within the conditions of STEP 1. It should not be lifted out of the study and treated as a universal expectation or a directly comparable score against a different trial.
For further product-specific technical information, see the Semaglutide research listing.
Tirzepatide: a dual GIP and GLP-1 profile
Tirzepatide is designed to activate both GIP and GLP-1 receptors. This dual profile adds a second incretin pathway, creating pharmacology that cannot be reduced to “semaglutide plus one more receptor”. The balance of activity across the two targets is part of the molecule’s specific design.
The landmark SURMOUNT-1 trial, published in 2022, enrolled 2,539 adults with obesity or overweight and at least one weight-related complication, excluding diabetes. Over 72 weeks, mean body-weight changes were −15.0%, −19.5% and −20.9% across the three tirzepatide dose groups, compared with −3.1% for placebo.
Again, those values describe SURMOUNT-1. They are not a head-to-head comparison with STEP 1, because the studies were conducted independently and differed in protocol, participants, treatment duration and analysis.
For analytical and handling documentation, see the Tirzepatide research listing.
Retatrutide: a triple GIP, GLP-1 and glucagon profile
Retatrutide is an investigational molecule designed to activate GIP, GLP-1 and glucagon receptors. It is sometimes informally called a “GLP-3”, but that term is scientifically inaccurate: there is no GLP-3 receptor in this mechanism. “Triple receptor agonist” is the clearer description.
In the 2023 Phase 2 obesity trial, 338 adults were followed for 48 weeks. Mean body-weight changes ranged from −8.7% to −24.2% across the retatrutide groups, compared with −2.1% for placebo. The wide range reflects different study groups and reinforces why the protocol matters.
Retatrutide has since progressed into Phase 3 research. Its developer reported initial Phase 3 topline findings during 2026, while noting that detailed results from parts of the programme remain subject to conference presentation and peer-reviewed publication. Crucially, retatrutide is still investigational and is not approved by any regulatory agency.
Our earlier guide, What Is Retatrutide? Triple-Agonist Peptide Research Explained, explores this mechanism in more detail. You can also view the Retatrutide research listing.
Why the headline percentages cannot be ranked directly
Placing −14.9%, −20.9% and −24.2% in a row is visually tempting. Scientifically, it is incomplete. Each number came from a different trial, and differences between those trials can materially affect the outcome.
| Design feature | STEP 1 | SURMOUNT-1 | Retatrutide Phase 2 |
|---|---|---|---|
| Published | 2021 | 2022 | 2023 |
| Participants | 1,961 | 2,539 | 338 |
| Duration | 68 weeks | 72 weeks | 48 weeks |
| Development stage | Phase 3 | Phase 3 | Phase 2 |
A defensible comparison should ask whether the populations, inclusion criteria, background interventions, outcome definitions, estimands, discontinuation rules and follow-up periods match. Unless the molecules are tested within the same randomised protocol, any ranking remains an indirect inference rather than a direct result.
What receptor count can—and cannot—tell us
The single–dual–triple framework is helpful for describing molecular strategy:
- It can tell us which receptor systems a molecule was designed to activate.
- It can suggest why researchers are testing different combinations of metabolic pathways.
- It cannot prove superior effectiveness, tolerability or suitability.
- It cannot replace properly controlled clinical evidence.
More receptor targets can produce broader biological activity, but broader is not automatically better. The relevant questions are how strongly and selectively each target is engaged, what effects appear at clinically studied exposures, how consistently those effects are reproduced, and what safety findings emerge over time.
Evidence maturity is part of the comparison
Semaglutide and tirzepatide have large clinical development programmes and authorised prescription uses. Retatrutide remains an investigational drug in Phase 3 development. That distinction affects how much is known about each molecule, how results have been scrutinised and what conclusions can responsibly be drawn.
Early and mid-stage trials are designed to answer important questions, but they do not establish the complete benefit–risk profile of a medicine. Sponsor announcements can provide timely information, yet peer-reviewed publications and regulatory assessments add detail that topline figures cannot.
The responsible conclusion: these are three distinct molecules at different stages of evidence maturity. Their receptor profiles can be compared directly; their results should be interpreted within their individual trial designs.
Frequently asked questions
What receptors does semaglutide target?
Semaglutide is classified as a GLP-1 receptor agonist.
What receptors does tirzepatide target?
Tirzepatide is a dual agonist that targets GIP and GLP-1 receptors.
What receptors does retatrutide target?
Retatrutide is an investigational triple agonist targeting GIP, GLP-1 and glucagon receptors.
Is retatrutide a “GLP-3”?
No. “GLP-3” is an informal internet label, not the scientific name of its mechanism. Retatrutide activates three receptor systems; it does not act on a receptor called GLP-3.
Does a triple agonist automatically outperform a dual or single agonist?
No. Receptor count alone cannot determine clinical effectiveness, safety or suitability. Those questions require controlled evidence, ideally including direct head-to-head trials.
Is retatrutide approved?
No. As of 18 September 2026, its developer states that retatrutide remains investigational and is not approved by any regulatory agency.
Can the headline weight-change figures be compared directly?
Not as if they came from the same experiment. STEP 1, SURMOUNT-1 and the retatrutide Phase 2 trial differed in size, duration, protocol and development stage. A cross-trial comparison can generate hypotheses, but it is not a direct ranking.
Continue your research
- Browse UK research peptides
- Peptide glossary: key research terms explained
- What Is Retatrutide? Triple-Agonist Peptide Research Explained
References
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine. 2021. PubMed record.
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. 2022. PubMed record.
- Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity—A Phase 2 Trial. New England Journal of Medicine. 2023. PubMed record.
- Eli Lilly and Company. What to know about retatrutide. Accessed 18 September 2026. Developer status page.
Research-use notice
Helix Bio materials are supplied strictly for laboratory research and analytical use. They are not medicines, are not for human or veterinary use, and must not be used for diagnosis, treatment or self-administration. References to published clinical studies concern the named pharmaceutical research programmes and do not imply equivalence with any research material sold by Helix Bio.
Last reviewed: 18 September 2026.