Retatrutide vs tirzepatide vs semaglutide at a glance
| Retatrutide | Tirzepatide | Semaglutide | |
|---|---|---|---|
| Developer and code | Eli Lilly, LY3437943 | Eli Lilly, LY3298176 | Novo Nordisk |
| Receptors | GIP, GLP-1 and glucagon | GIP and GLP-1 | GLP-1 |
| Agonist type | Triple | Dual | Single |
| Length | 39 amino acids | 39 amino acids | 31 amino acids |
| Half-life (approx.) | 6 days | 5 days | 7 days |
| Key obesity trial | Phase 2 (NEJM 2023); TRIUMPH-1 | SURMOUNT-1 (NEJM 2022) | STEP 1 (NEJM 2021) |
| Top-dose mean weight loss | 24.2% at 48 weeks (phase 2); 28.3% at 80 weeks (TRIUMPH-1 topline) | 20.9% at 72 weeks (15 mg) | 14.9% at 68 weeks (2.4 mg) |
| Australian status | Investigational, not on the ARTG | Registered as Mounjaro (prescription) | Registered as Ozempic and Wegovy (prescription) |
| Chainwell Peptide research formats | 10, 20, 30 mg vials; 10 mg pen | 2 mg vial; 3 mL pen | Not stocked |
The weight figures come from different trials with different populations and durations, so they are not a direct comparison. Tirzepatide and retatrutide share a length and a similar design lineage: both are Lilly peptides with a C20 fatty diacid for albumin binding.
Receptors: what the glucagon component adds
Semaglutide works through GLP-1 alone: insulin release, slower gastric emptying and appetite reduction. Tirzepatide adds GIP, and it is actually more potent at the GIP receptor than at GLP-1. Retatrutide keeps that GIP-heavy balance (structural work in Cell Discovery in 2024 put it at about 8.9 times native GIP potency) and adds partial glucagon receptor activity, at about 0.3 times native glucagon.
Glucagon receptor activity raises energy expenditure and drives fat breakdown in the liver. That is the plausible reason retatrutide's liver fat results were so large (86.0% relative reduction at 48 weeks on 12 mg in the Nature Medicine 2024 substudy), and why researchers treat it as a separate question rather than a stronger tirzepatide. For more on the molecule itself, see what retatrutide is.
Tirzepatide vs retatrutide: trial results side by side
Each compound's flagship obesity trial, in adults without diabetes:
- Tirzepatide, SURMOUNT-1 (Jastreboff et al., NEJM, 2022): 72 weeks, mean weight change of 15.0% (5 mg), 19.5% (10 mg) and 20.9% (15 mg), against 3.1% on placebo.
- Retatrutide, phase 2 (Jastreboff et al., NEJM, 2023): 48 weeks, 17.1% (4 mg), 22.8% (8 mg) and 24.2% (12 mg), against 2.1% on placebo.
- Retatrutide, TRIUMPH-1 (Lilly topline, May 2026): 80 weeks, 19.0% (4 mg), 25.9% (9 mg) and 28.3% (12 mg).
- Semaglutide 2.4 mg, STEP 1 (Wilding et al., NEJM, 2021): 68 weeks, 14.9% against 2.4% on placebo.
Tirzepatide and semaglutide have also been compared directly: in SURMOUNT-5 (NEJM, 2025), tirzepatide produced 20.2% weight loss against 13.7% for semaglutide at 72 weeks. The equivalent retatrutide trial is TRIUMPH-5, about 800 adults randomised to retatrutide or tirzepatide with an 80-week weight endpoint. ClinicalTrials.gov lists its estimated completion as December 2026. Until it reports, anyone claiming to know what's better, tirzepatide or retatrutide, is comparing across trials. Our retatrutide results guide has the full timepoint data.
Side effects compared
All three share the incretin side effect profile: nausea, diarrhoea, vomiting and constipation, dose related and concentrated in escalation. The numbers at the top doses:
| Retatrutide 12 mg (TRIUMPH-1) | Tirzepatide 15 mg (SURMOUNT-1) | Semaglutide 2.4 mg (STEP 1) | |
|---|---|---|---|
| Nausea | 42.4% | 31.0% | about 44% |
| Vomiting | 25.3% | 12.2% | about 25% |
| Stopped due to adverse events | 11.3% | 6.2% | 7.0% |
| Placebo stop rate | 4.9% | 2.6% | 3.1% |
Retatrutide also has a signal the others do not: dysesthesia, an altered skin sensation, reported in 20.9% of the 12 mg group in TRIUMPH-4 against 0.7% on placebo. And tirzepatide and semaglutide have years of post-marketing safety data, which retatrutide cannot have until it is approved. Details are in our retatrutide side effects guide.
Retatrutide vs Mounjaro and retatrutide vs Ozempic
Mounjaro is the brand name for tirzepatide, registered by the TGA for type 2 diabetes and, since September 2024, for chronic weight management in adults. Ozempic is semaglutide registered for type 2 diabetes in Australia; Wegovy is the semaglutide product registered for weight management. All three are prescription medicines. So retatrutide vs Mounjaro is really retatrutide vs tirzepatide, and retatrutide vs Ozempic is retatrutide vs semaglutide at diabetes doses (STEP 1 used the 2.4 mg Wegovy dose).
The practical difference in Australia is regulatory, not pharmacological. Mounjaro and Ozempic have been evaluated by the TGA for quality, safety and efficacy. Retatrutide has not, and the TGA has warned against using it outside a clinical trial. Research-grade tirzepatide from a peptide supplier is also not Mounjaro: it is not a registered medicine, has not been assessed by the TGA, and is sold for laboratory work only. More on the Australian position is in is retatrutide available in Australia.
Choosing between them for laboratory research
Our view: for a lab, the question is rarely which compound is better; it is which receptor contribution you need to isolate. Tirzepatide is the better-characterised reference compound, with a large published literature, so it makes the natural dual-agonist comparator. Retatrutide is the variable when the study asks what glucagon receptor activity adds, for example in energy expenditure or liver lipid work. Many designs run both, and add cagrilintide, a long-acting amylin analogue, to probe a separate satiety pathway.
Formats matter too. Research tirzepatide comes as a 2 mg vial or as the Tirzepatide Pen in a 3 mL cartridge, and retatrutide as 10, 20 and 30 mg vials or the 10 mg Retatrutide Pen. Every lot of each is tested by an independent laboratory for identity by mass spectrometry and purity by HPLC, with the lot number on the vial matching its certificate on the COA lookup. The retatrutide calculator handles reconstitution volumes, and both sit in our metabolic research peptides range.
Research use only: Chainwell Peptide supplies these compounds for laboratory research, not for human or veterinary use. Nothing on this page is medical advice or a recommendation to use any product.
Frequently asked questions
Is retatrutide stronger than tirzepatide?
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In separate trials, retatrutide produced larger average weight reductions: 24.2% at 48 weeks in phase 2 and 28.3% at 80 weeks in TRIUMPH-1, against 20.9% at 72 weeks for tirzepatide in SURMOUNT-1. These trials differ in design, so they are not a direct comparison. The head-to-head TRIUMPH-5 trial is expected to complete in late 2026.
What is the difference between retatrutide and Mounjaro?
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Mounjaro is tirzepatide, a dual GIP and GLP-1 agonist registered by the TGA as a prescription medicine for type 2 diabetes and weight management. Retatrutide adds glucagon receptor activity, making it a triple agonist, and it is still investigational, with no approval in Australia or elsewhere. Both are made by Eli Lilly.
Is retatrutide better than Ozempic?
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Cross-trial figures favour retatrutide for weight: 24.2% at 48 weeks in phase 2, against 14.9% at 68 weeks for semaglutide 2.4 mg in STEP 1. But Ozempic is a TGA-registered diabetes medicine with years of safety data, while retatrutide is unapproved and its long-term safety is unknown. Better depends on evidence that does not exist yet.
Is research tirzepatide the same as Mounjaro?
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No. Mounjaro is a registered medicine made under TGA-assessed manufacturing and supplied on prescription. Research-grade tirzepatide from a peptide supplier is the same molecule by identity testing, but it is not a registered medicine, has not been assessed by the TGA, and is sold for laboratory research only, not for human use.
