Retatrutide vs Tirzepatide: How They Compare, With Semaglutide Too
The gap between retatrutide and tirzepatide is a single receptor. Tirzepatide switches on GIP and GLP-1, while retatrutide also brings glucagon into play, and in separate trials it delivered bigger average drops in body weight. The catch is status. In Australia tirzepatide is an approved medicine sold as Mounjaro, retatrutide remains investigational, and nobody has yet published a trial pitting the two directly against each other.
Buy Retatrutide or Tirzepatide Australia Wide, Compared Side by Side
| Retatrutide | Tirzepatide | Semaglutide | |
|---|---|---|---|
| Developer and research code | Eli Lilly, LY3437943 | Eli Lilly, LY3298176 | Novo Nordisk |
| Receptor targets | GIP, GLP-1 and glucagon | GIP and GLP-1 | GLP-1 |
| Class of agonist | Triple | Dual | Single |
| Peptide length | 39 amino acids | 39 amino acids | 31 amino acids |
| Approximate half-life | 6 days | 5 days | 7 days |
| Main obesity trial | Phase 2 (NEJM 2023); TRIUMPH-1 | SURMOUNT-1 (NEJM 2022) | STEP 1 (NEJM 2021) |
| Mean weight loss at top dose | Phase 2 gave 24.2% by week 48, and the TRIUMPH-1 topline gave 28.3% by week 80 | 15 mg gave 20.9% by week 72 | 2.4 mg gave 14.9% by week 68 |
| Status in Australia | Investigational, not on the ARTG | Registered as Mounjaro (prescription) | Registered as Ozempic and Wegovy (prescription) |
| NovaPep research formats | 10, 20, 30 mg vials; 10 mg pen | 3 mL pen | Not stocked |
Because the weight numbers were drawn from separate trials with their own populations and timeframes, they cannot be lined up as a true comparison. Retatrutide and tirzepatide share the same length and a related design history. Each is a Lilly peptide carrying a C20 fatty diacid that binds albumin.
Order Retatrutide Online and See What Glucagon Activity Brings
Semaglutide relies on GLP-1 by itself, which drives insulin release, slows stomach emptying and dampens appetite. Tirzepatide layers GIP on top and is in fact stronger at the GIP receptor than at GLP-1. Retatrutide holds on to that GIP-weighted balance, which a 2024 structural paper in Cell Discovery estimated at roughly 8.9 times native GIP potency, and adds partial activity at the glucagon receptor of around 0.3 times native glucagon.
Activating the glucagon receptor lifts energy expenditure and pushes the liver to break down fat. That offers a reasonable explanation for the striking liver fat findings, an 86.0% relative reduction after 48 weeks on 12 mg in the 2024 Nature Medicine substudy. It is also why researchers view retatrutide as its own question and not simply a more powerful tirzepatide. Our page on what retatrutide is covers the molecule in more depth. You can buy retatrutide online in Australia in 10, 20 or 30 mg vials, or as a 10 mg pen.
Shop Tirzepatide and Retatrutide With the Trial Numbers in Hand
Below are the headline obesity trials for each compound, all run in adults who did not have diabetes.
- Tirzepatide, SURMOUNT-1 (Jastreboff et al., NEJM, 2022). Over 72 weeks, mean weight change reached 15.0% on 5 mg, 19.5% on 10 mg and 20.9% on 15 mg, compared with 3.1% on placebo.
- Retatrutide, phase 2 (Jastreboff et al., NEJM, 2023). Over 48 weeks, the figures were 17.1% on 4 mg, 22.8% on 8 mg and 24.2% on 12 mg, compared with 2.1% on placebo.
- Retatrutide, TRIUMPH-1 (Lilly topline, May 2026). At the 80-week mark the 12 mg group averaged a 28.3% loss, the 9 mg group 25.9% and the 4 mg group 19.0%.
- STEP 1, semaglutide 2.4 mg (NEJM, 2021, Wilding et al.). After 68 weeks the average loss stood at 14.9%, while placebo managed 2.4%.
Tirzepatide has already gone up against semaglutide directly. In SURMOUNT-5 (NEJM, 2025) it achieved 20.2% weight loss at 72 weeks, compared with 13.7% for semaglutide. Retatrutide's matching study is TRIUMPH-5, which randomises roughly 800 adults to retatrutide or tirzepatide and measures weight at 80 weeks. ClinicalTrials.gov gives December 2026 as its estimated completion. Until those results land, any verdict on whether tirzepatide or retatrutide is better rests on comparisons across separate trials. Every timepoint is set out in our retatrutide results guide. Order the tirzepatide pen online in Australia, a 3 mL research format, when a study needs that comparator.
Buy Retatrutide for Sale With a Clear View of Side Effects
The three compounds have the same incretin pattern of adverse effects. Nausea, diarrhoea, vomiting and constipation rise with dose and cluster during escalation. Here is how the top doses compare.
| TRIUMPH-1, retatrutide at 12 mg | SURMOUNT-1, tirzepatide at 15 mg | STEP 1, semaglutide at 2.4 mg | |
|---|---|---|---|
| Rate of nausea | 42.4% | 31.0% | about 44% |
| Rate of vomiting | 25.3% | 12.2% | about 25% |
| Discontinued because of adverse events | 11.3% | 6.2% | 7.0% |
| Discontinuation on placebo | 4.9% | 2.6% | 3.1% |
One signal belongs to retatrutide alone. Dysesthesia, a change in skin sensation, appeared in 20.9% of the 12 mg group in TRIUMPH-4 compared with 0.7% on placebo. Tirzepatide and semaglutide also benefit from years of post-marketing safety monitoring, something retatrutide cannot have before approval. The full detail sits in our retatrutide side effects guide.
Order Retatrutide in Australia and Compare It With Mounjaro or Ozempic
Mounjaro is the trade name for tirzepatide. The TGA registered it for type 2 diabetes and, from September 2024, for long-term weight management in adults. In Australia Ozempic is semaglutide registered for type 2 diabetes, and Wegovy is the semaglutide product registered for weight management. Each of the three is a prescription medicine. Comparing retatrutide with Mounjaro therefore means comparing it with tirzepatide, and comparing it with Ozempic means comparing it with semaglutide at diabetes doses, bearing in mind that STEP 1 used the 2.4 mg Wegovy dose.
Here in Australia the real divide is regulatory rather than pharmacological. The TGA has assessed Mounjaro and Ozempic for quality, safety and efficacy. It has not assessed retatrutide, and it has cautioned against any use outside a clinical trial. Research-grade tirzepatide bought from a peptide supplier is not Mounjaro either. It is not a registered medicine, the TGA has not reviewed it, and it is sold only for laboratory work. Our page on is retatrutide available in Australia explains the local position further.
Shop Research Peptides Online and Pick the Right One for Your Lab
In our experience a lab is seldom asking which compound is better. The real question is which receptor contribution needs to be isolated. Tirzepatide has the deeper published literature and is the better-characterised reference, which makes it the obvious dual-agonist comparator. Retatrutide becomes the test variable when a study wants to know what glucagon receptor activity adds, for instance in energy expenditure or hepatic lipid work. Plenty of designs include both, then bring in cagrilintide, a long-acting amylin analogue, to explore a distinct satiety pathway. Shop cagrilintide online in 5 or 10 mg vials from our Australian stock.
Format is worth weighing as well. Research tirzepatide is supplied as the Tirzepatide Pen with a 3 mL cartridge, while retatrutide comes in 10, 20 and 30 mg vials or as the 10 mg Retatrutide Pen. Each lot of either compound passes the same independent testing, with mass spectrometry for identity and HPLC for purity, and the lot number on every vial leads to a certificate in the COA lookup. Reconstitution volumes are handled by the retatrutide calculator, and both products belong to our metabolic research peptides collection.
Buy Retatrutide and Tirzepatide Together for Head-to-Head Lab Work
When planning a head-to-head study, source both compounds from the same supplier so each certificate reports identity and purity in a matching format. A practical first order pairs the 10 mg retatrutide vial with the 2 mg tirzepatide vial. Groups that would like the comparator ready in solution can choose the Tirzepatide Pen instead. Planning an amylin arm as well? The 5 mg cagrilintide vial is also stocked. Order the whole set online from Australian stock, then add bacteriostatic water to match the number of vials you intend to reconstitute.
Research use only. NovaPep sells these compounds to adults 18+ for laboratory research, not for human or veterinary use. This page is not medical advice and does not recommend using any product.
Retatrutide vs Tirzepatide: How They Compare, With Semaglutide Too FAQ
Does retatrutide outperform tirzepatide?
Across separate trials, retatrutide gave bigger average weight reductions, with 24.2% at 48 weeks in phase 2 and 28.3% at 80 weeks in TRIUMPH-1, compared with 20.9% at 72 weeks for tirzepatide in SURMOUNT-1. Those trials were designed differently, so the numbers are not a direct match. TRIUMPH-5, the head-to-head study, is due to finish in late 2026.
How does retatrutide differ from Mounjaro?
Mounjaro is tirzepatide, a dual GIP and GLP-1 agonist that the TGA has registered as a prescription medicine for type 2 diabetes and weight management. Retatrutide also acts on the glucagon receptor, which makes it a triple agonist, and it is still investigational with no approval in Australia or any other country. Eli Lilly developed both.
How does retatrutide stack up against Ozempic?
For weight, cross-trial numbers lean towards retatrutide, at 24.2% after 48 weeks in phase 2 compared with 14.9% after 68 weeks for semaglutide 2.4 mg in STEP 1. Ozempic, though, is a TGA-registered diabetes medicine backed by years of safety data, whereas retatrutide is unapproved and its long-term safety remains unknown. A fair verdict needs evidence that has not yet been produced.
Is research-grade tirzepatide identical to Mounjaro?
No. Mounjaro is a registered medicine, produced under TGA-assessed manufacturing and dispensed on prescription. Tirzepatide from a research peptide supplier matches the same molecule on identity testing, yet it is not a registered medicine, the TGA has not assessed it, and it is sold only for laboratory research, never for human use.
Where do I order retatrutide and tirzepatide online in Australia?
NovaPep stocks both in Australia and sells them online for laboratory research. Retatrutide comes in three vial fills or a pen, and tirzepatide as a 2 mg vial or a 3 mL pen. Sourcing both from one supplier keeps the certificates consistent across every arm of a comparison study. Neither product is intended for human or veterinary use.