Semaglutide vs Tirzepatide vs Retatrutide: 2026 Metabolic Peptide Comparison
Share
By the ThePeptide Research Team · Every figure cited from its primary published trial · Last updated July 2026
Semaglutide, tirzepatide, and retatrutide represent three successive generations of incretin-based research peptides — single-, dual-, and triple-receptor agonists. In their respective pivotal trials, peak mean body-weight reductions rose from 14.9% (semaglutide, GLP-1) to 20.9% (tirzepatide, GIP/GLP-1) to 30.3% (retatrutide, GIP/GLP-1/glucagon). This guide compares their mechanisms, clinical data, safety, and molecular profiles for Canadian laboratory researchers, with each figure drawn from its own published trial.
Key takeaways
- More receptors, larger reported reductions. Peak trial weight loss rose from 14.9% (single GLP-1) to 20.9% (dual GIP/GLP-1) to 30.3% (triple GIP/GLP-1/glucagon).
- Not a head-to-head study. Each figure comes from a separate trial and population — the numbers show a trend, not a controlled comparison.
- Two approved, one investigational. Semaglutide and tirzepatide are approved drugs in some markets; retatrutide is Phase 3. All material here is research-use-only.
- Same GI-dominant safety pattern. All three reported dose-dependent nausea, diarrhea, and vomiting in trials, hence stepwise escalation.
- Pick by research question, not "strength" — single-target, dual, or triple-agonist pharmacology.
At a Glance
| Feature | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Receptor targets | GLP-1 (single) | GIP + GLP-1 (dual) | GIP + GLP-1 + glucagon (triple) |
| Peak trial reduction | 14.9% (STEP 1) | 20.9% (SURMOUNT-1) | 30.3% (TRIUMPH-1) |
| Pivotal trial | STEP 1, 68 wks | SURMOUNT-1, 72 wks | TRIUMPH-1, 104 wks |
| Developer | Novo Nordisk | Eli Lilly | Eli Lilly |
| Regulatory status | Approved (Ozempic/Wegovy) | Approved (Mounjaro/Zepbound) | Phase 3 (investigational) |
| Amino acids | 31 | 39 | 34 |
| CAS number | 910463-68-2 | 2023788-19-2 | 2381089-83-2 |
| Dosing cadence (trials) | Once weekly | Once weekly | Once weekly |
| Full research guide | Semaglutide | Tirzepatide | Retatrutide |
Mechanism: Single vs Dual vs Triple Agonism
The defining difference between these three peptides is how many incretin/metabolic receptors each engages:
- Semaglutide — single (GLP-1). A GLP-1 receptor agonist associated with glucose-dependent insulin secretion, glucagon suppression, delayed gastric emptying, and central appetite signaling. Read the full semaglutide guide.
- Tirzepatide — dual (GIP + GLP-1). Adds a second incretin pathway (GIP) to GLP-1 in one molecule — the "twincretin" concept. Read the full tirzepatide guide.
- Retatrutide — triple (GIP + GLP-1 + glucagon). Layers glucagon-receptor agonism, associated with increased energy expenditure, on top of the GIP/GLP-1 pair. Read the full retatrutide guide.
Researchers hypothesize that adding pathways — appetite-related incretin signaling plus a metabolic-rate pathway — is what tracks with the larger reductions seen across the trials. ↑ Back to top
Clinical Weight-Loss Data
The headline figures below are each from the compound's own pivotal obesity trial. They are not from a single head-to-head study, so direct numeric comparison should be read with that caveat.
| Compound | Trial (citation) | Dose & duration | Mean weight reduction |
|---|---|---|---|
| Semaglutide | STEP 1 (Wilding et al., NEJM 2021) | 2.4 mg weekly, 68 wks | −14.9% (vs −2.4% placebo) |
| Tirzepatide | SURMOUNT-1 (Jastreboff et al., NEJM 2022) | 15 mg weekly, 72 wks | −20.9% (vs −3.1% placebo) |
| Retatrutide | TRIUMPH-1 (Eli Lilly, 2026) | 12 mg weekly, 104 wks | −30.3% |
The trend from single to dual to triple agonism corresponds with progressively larger reported reductions. For the underlying titration schedules and doses studied, see our research dosing reference. ↑ Back to top
Safety Comparison
Across all three compounds the most frequently reported adverse events in the trials were gastrointestinal and dose-dependent — predominantly nausea, diarrhea, vomiting, and constipation — which is why each trial program used gradual stepwise dose escalation rather than starting at the maintenance dose. In the retatrutide TRIUMPH-1 program the reported rates at the 12 mg dose were nausea ~42%, diarrhea ~32%, constipation ~26%, and vomiting ~25%, with treatment discontinuation of 11.3% versus 4.9% for placebo; the semaglutide and tirzepatide programs reported the same GI-dominant pattern. These figures describe outcomes in supervised clinical trial populations, reported for reference only. ↑ Back to top
Molecular Profiles
| Property | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| CAS number | 910463-68-2 | 2023788-19-2 | 2381089-83-2 |
| Molecular formula | C187H291N45O59 | C225H348N48O68 | (lipidated 34-mer) |
| Molar mass | ~4113.6 g/mol | ~4813.5 g/mol | lipidated 34-aa peptide |
| Amino acids | 31 | 39 | 34 |
| Structure | Fatty-acid (albumin-binding) | Fatty-acid (C20 diacid) | Fatty-acid lipidated |
All three are fatty-acid-modified peptides whose albumin binding supports once-weekly dosing. ↑ Back to top
Choosing a Compound for Research
Selection is a function of the research question, not personal use. In practice, researchers reference: semaglutide as the extensively characterized single-target GLP-1 benchmark; tirzepatide when studying dual GIP/GLP-1 "twincretin" pharmacology; and retatrutide when investigating triple-agonist activity and the added glucagon/energy-expenditure arm. All three are supplied by ThePeptide as independently tested, Canadian-shipped lyophilized powder. To prepare working solutions, use the reconstitution calculator and the bacteriostatic water chart. ↑ Back to top
Semaglutide (GLP-1) — Summary
The most-studied GLP-1 receptor agonist (Novo Nordisk; Ozempic/Wegovy). In STEP 1 it reached −14.9% at 68 weeks. It is the standard single-receptor reference compound. Full details, molecular data, and sourcing are in the Semaglutide Canada research guide, and product options are Semaglutide 5mg and 10mg.
Tirzepatide (GIP/GLP-1) — Summary
The first dual GIP/GLP-1 agonist (Eli Lilly; Mounjaro/Zepbound). In SURMOUNT-1 it reached −20.9% at 72 weeks. Full details are in the Tirzepatide Canada research guide; products are Tirzepatide 5mg and 10mg.
Retatrutide (Triple Agonist) — Summary
The first triple GIP/GLP-1/glucagon agonist (Eli Lilly; investigational). In Phase 3 TRIUMPH-1 it reached −30.3% at 104 weeks. Full details are in the Retatrutide Canada research guide, with side-effect detail in retatrutide side effects; the product is Retatrutide 10mg.
How to buy research peptides in Canada →
Frequently Asked Questions
Which is stronger: semaglutide, tirzepatide, or retatrutide?
By peak reported weight reduction in each compound's pivotal trial, retatrutide (30.3%, TRIUMPH-1) exceeded tirzepatide (20.9%, SURMOUNT-1), which exceeded semaglutide (14.9%, STEP 1). These are separate trials, not a head-to-head study, and are reported here for research reference only.
What is the mechanistic difference between them?
Semaglutide is a single GLP-1 agonist, tirzepatide is a dual GIP/GLP-1 agonist, and retatrutide is a triple GIP/GLP-1/glucagon agonist. Each added receptor engages a further metabolic pathway.
Are any of them approved?
Semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound) are approved as drugs in some markets; retatrutide is investigational (Phase 3). All material sold by ThePeptide is research-use-only, not the approved drug products, and not for human consumption.
Which should I choose for research?
It depends on the research question — semaglutide for single-target GLP-1 work, tirzepatide for dual GIP/GLP-1 pharmacology, retatrutide for triple-agonist and glucagon-arm studies. See the individual guides for full detail.
Do they share the same side-effect profile?
All three reported predominantly gastrointestinal, dose-dependent adverse events (nausea, diarrhea, vomiting, constipation) in their trials, which is why stepwise dose escalation was used. Reported for reference only.
How are these peptides reconstituted?
All three are lyophilized powders reconstituted with bacteriostatic water. Use our reconstitution calculator to determine concentration and syringe units. This is laboratory technique only.
Related Research Resources
- Retatrutide Canada guide · Tirzepatide Canada guide · Semaglutide Canada guide
- Research dosing & reconstitution reference
- Peptide reconstitution calculator · How much bacteriostatic water to add
- Where to get research peptides tested in Canada
- How to buy research peptides in Canada
References
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384:989-1002. DOI: 10.1056/NEJMoa2032183.
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216. DOI: 10.1056/NEJMoa2206038. PMID: 35658024.
- Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity (Phase 2). N Engl J Med. 2023;389:514-526. DOI: 10.1056/NEJMoa2301972.
- Eli Lilly and Company. Retatrutide Phase 3 TRIUMPH-1 topline results, May 2026.