Retatrutide (Eli Lilly code LY3437943) is a synthetic peptide that simultaneously activates three hormonal receptors: GIP, GLP-1, and glucagon. Since the publication of its first phase 2 results, it has emerged as the most effective incretin molecule ever studied. For Canadian researchers and buyers, here are the 8 numbers that summarize what the published literature has demonstrated, followed by criteria for evaluating a serious supplier.
1. 24.2%: average weight loss at 12 mg over 48 weeks
This is the central figure. A phase 2 study published in the New England Journal of Medicine on 338 obese adults established the molecule's dose-response relationship over 48 weeks of weekly subcutaneous treatment. At the highest dose (12 mg), average weight loss reached 24.2%, compared with 2.1% on placebo. No incretin molecule had ever shown such a result in a controlled trial.
2. 22.1% vs 16.5%: retatrutide beats tirzepatide in network meta-analysis
A network meta-analysis published in Metabolism in 2024 covering seven GLP-1 agonists directly compared the molecules based on randomized trials. Retatrutide at 12 mg produced a 22.1% reduction in body weight, followed by retatrutide 8 mg (20.7%), then tirzepatide 15 mg (16.5%). The authors conclude that triple agonists outperform double agonists, which outperform single agonists. The hierarchy is clear.
3. 17 cm: the waist-circumference reduction at the maximum dose
The same 2024 meta-analysis documents an average waist-circumference reduction of 17 cm with retatrutide 12 mg. This data point matters because the loss of visceral adipose tissue (measured by waist circumference) is a better predictor of metabolic health than gross weight. The effect on body composition goes beyond what shows up on the scale.
4. OR 54.6: the odds ratio for achieving more than 15% weight loss
The Bayesian meta-analysis published in Obesity in 2025 compared retatrutide with the main current incretin agonists across 19 randomized trials totaling 29,506 adults. Retatrutide showed the highest odds ratio for reaching 15% or more of weight loss (OR 54.6), compared with 16.4 for double agonists and 9.0 for single GLP-1s. Statistically, a patient on retatrutide is 6 times more likely to cross the 15% threshold than a patient on a single GLP-1.
5. 2.02%: the HbA1c drop in type 2 diabetics over 24 weeks
A phase 2 study published in The Lancet in 2023 on 281 diabetic adults showed a 2.02% reduction in glycated hemoglobin (HbA1c) at 24 weeks with the 12 mg dose, clearly more than dulaglutide at 1.5 mg used as the active comparator. For reference: a 1% drop in HbA1c already significantly reduces the risk of micro and macrovascular complications. A 2% drop is exceptional.
6. 29,506 participants: the database that solidifies the profile
This is the cumulative total of adults included in the 19 randomized trials analyzed by the 2025 Obesity meta-analysis. When evaluating a peptide that is not yet approved, the size of the evidence base counts as much as the individual numbers. Nearly 30,000 patients studied places retatrutide well above the usual statistical fragility threshold of new molecules.
7. 0 to 26%: discontinuations for adverse effects, vs 0 to 9% on placebo
The Annals of Internal Medicine 2025 review covering 26 trials and 15,491 participants confirms a safety profile broadly comparable to other incretin agonists, with treatment discontinuations for adverse effects in 0 to 26% of cases (vs 0 to 9% on placebo). Gastrointestinal effects (nausea, vomiting, diarrhea) are dose-dependent and attenuated by gradual titration starting at 2 mg. No cases of severe hypoglycemia or death were reported in the published trials.
8. 2027 to 2028: the possible approval window
Eli Lilly is currently running phase 3 trials (the TRIUMPH program). According to pharmaceutical analysts, approval is expected between 2027 and 2028, subject to final results and the opinion of regulatory agencies. As you read this guide in 2026, retatrutide is therefore not approved by Health Canada for clinical use. It is available exclusively for research purposes, in compliance with the regulatory frameworks applicable to research peptides.
Quick comparison with other incretins
| Molecule | Most effective weekly dose | Long-term weight loss |
|---|---|---|
| Retatrutide | 12 mg | 22 to 24% |
| Tirzepatide | 15 mg | 16 to 18% |
| Semaglutide | 2.4 mg | 14 to 17% |
| Liraglutide | 3 mg/day | 5 to 6% |
Source: Metabolism 2024 meta-analysis and Annals of Internal Medicine 2025.
Criteria for evaluating a retatrutide supplier in Canada
The numbers above mean nothing if the molecule received does not meet specifications. Four criteria should guide the choice:
- Up-to-date Certificate of Analysis (COA), dated and signed by an independent third-party laboratory. Recommended methods: HPLC for purity, mass spectrometry for identity, sterility testing for endotoxins.
- Minimum purity of 98%, ideally above 99% for reconstituted retatrutide.
- Controlled storage and shipping conditions: lyophilized and stored at -20 °C, refrigerated shipping.
- Supply-chain transparency: country of origin of the peptide, identification of the synthesis laboratory, batch traceability.
Reborn Peptide operates exclusively in the research segment, with a verified supply chain and products accompanied by their technical data sheet.
Frequently asked questions
Is retatrutide legal in Canada?
For human clinical use, no, because it is not approved by Health Canada. For research, the purchase and possession of research peptides fall within a specific regulatory framework distinct from that of prescription drugs. Reborn Peptide markets its products exclusively for research purposes.
What is the difference between retatrutide and tirzepatide?
Tirzepatide is a dual agonist (GLP-1 and GIP). Retatrutide adds the glucagon receptor, which increases resting energy expenditure on top of the effects on satiety and glucose metabolism. That is what explains the 5 to 6 percentage point gap in weight loss in the published indirect comparisons.
When will retatrutide be commercially available?
Eli Lilly is currently running phase 3 trials (the TRIUMPH program). Possible approval is expected in 2027 or 2028 according to pharmaceutical analysts, subject to final results and the opinion of regulatory agencies.
How should retatrutide be stored?
In lyophilized form at -20 °C before reconstitution. Once reconstituted with bacteriostatic water, at 2 to 8 °C, with typical research use within 28 days.
Does retatrutide cause serious side effects?
The published trials mainly report mild to moderate gastrointestinal effects. Serious adverse events are rare (0 to 10% vs 0 to 12% on placebo depending on the studies). As with any research product, use outside a controlled clinical setting is not recommended.
Going further
For Canadian researchers interested in retatrutide, the Reborn Peptide catalog brings together the most-studied research peptides currently available. Always check the certificate of analysis provided with each batch, and consult published trials on PubMed for the most recent research protocols.
Important notice: this content is provided for informational and research purposes only. The peptides discussed are not approved for human consumption in Canada and are not intended to diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare professional before making any decisions related to your health.
