Mounjaro vs Retatrutide: Which Causes More Weight Loss?
Mounjaro contains tirzepatide, an approved dual GIP/GLP-1 medicine. Retatrutide is an investigational triple GIP/GLP-1/glucagon agonist. The newest Phase 3 data put retatrutide ahead on average total weight loss — but there has not yet been a direct head-to-head trial between the two.
In separate Phase 3 trials, retatrutide 12 mg produced up to 28.3% average body-weight reduction at 80 weeks, compared with 20.9% for tirzepatide 15 mg at 72 weeks in SURMOUNT-1. That strongly suggests retatrutide may be the more powerful weight-loss drug — but it does not prove superiority because the drugs have not been compared head-to-head.
Mounjaro vs Retatrutide: quick comparison
Important: These are results from different trials with different designs, durations and populations. Cross-trial comparisons are useful for context, but they are not equivalent to a randomized head-to-head study.
| Feature | Mounjaro / Tirzepatide | Retatrutide |
|---|---|---|
| Receptors | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Australian status | TGA-approved for type 2 diabetes and chronic weight management | Investigational; not TGA-approved |
| Major obesity Phase 3 result | 20.9% average at 72 weeks, 15 mg | 28.3% average at 80 weeks, 12 mg |
| Longer-term data | Up to 19.7% at 176 weeks in participants with obesity + prediabetes | Up to 30.3% at 104 weeks in a selected extension subgroup |
| Approval maturity | Established prescription medicine | Still awaiting regulatory submissions/assessment |
| Evidence confidence today | More mature | Very promising, still investigational |
What the latest Phase 3 trials actually show
Retatrutide: TRIUMPH-1
Lilly reported the pivotal TRIUMPH-1 Phase 3 results in May 2026. In adults with obesity or overweight plus a weight-related condition, without diabetes, the 12 mg arm produced 28.3% average weight reduction at 80 weeks using the efficacy estimand.
At 12 mg, 45.3% of participants lost at least 30% of their starting body weight. A selected extension group with baseline BMI ≥35 reached an average 30.3% reduction at 104 weeks.
Tirzepatide: SURMOUNT-1
In the pivotal SURMOUNT-1 Phase 3 trial, tirzepatide produced average weight reductions of 15.0%, 19.5% and 20.9% at 72 weeks with 5 mg, 10 mg and 15 mg, respectively.
At the 15 mg dose, about 56.7% lost at least 20% of their starting weight under the treatment-regimen analysis.
Retatrutide: TRIUMPH-2
In July 2026, Lilly reported that adults with obesity or overweight and type 2 diabetes lost up to an average of 20.8% at 80 weeks with retatrutide 12 mg.
Retatrutide: TRIUMPH-3
In adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes, Lilly reported up to 22.6% average weight loss at 80 weeks.
Weight loss is not identical to fat loss. These headline trials primarily report change in total body weight. It is therefore more accurate to say retatrutide has produced greater average weight loss in separate trials, rather than claiming a proven head-to-head advantage specifically in fat mass.
Why might Retatrutide produce more weight loss?
The biggest biological difference is the third receptor. Tirzepatide targets GIP and GLP-1. Retatrutide targets those same two pathways and also activates the glucagon receptor.
GLP-1
Helps reduce appetite, slows gastric emptying and improves glucose regulation.
GIP
Works alongside GLP-1 and contributes to glucose control and metabolic effects.
Glucagon receptor
Retatrutide adds glucagon receptor activity, which is being studied for its effects on energy expenditure and metabolism. This extra pathway is a plausible reason for the larger weight reductions seen in trials.
The practical result
The current trial numbers suggest the triple-agonist approach can push average weight reduction beyond what has historically been seen with tirzepatide.
Mounjaro vs Retatrutide: pros and cons
Mounjaro — Pros
- TGA-approved in Australia for chronic weight management.
- Large Phase 3 evidence base with years of follow-up.
- Very strong average weight loss.
- Established prescribing, pharmacy and safety-monitoring pathway.
- Three-year data show sustained weight reduction in people with obesity and prediabetes.
Mounjaro — Cons
- Average weight loss in SURMOUNT-1 was lower than the headline TRIUMPH-1 retatrutide result.
- Common gastrointestinal side effects include nausea, diarrhoea, vomiting and constipation.
- Some users report plateaus after substantial initial weight loss.
Retatrutide — Pros
- Largest average weight-loss numbers currently reported from a major incretin obesity trial.
- 28.3% average reduction at 80 weeks in the 12 mg TRIUMPH-1 efficacy analysis.
- 45.3% of 12 mg participants reached at least 30% weight reduction.
- Triple GIP/GLP-1/glucagon mechanism may provide additional metabolic effects.
Retatrutide — Cons
- Still investigational and not TGA-approved.
- No direct head-to-head trial against tirzepatide yet.
- Higher-dose TRIUMPH-1 arms had substantial gastrointestinal side effects.
- Dysesthesia was reported more often than with placebo in TRIUMPH-1.
- Products sold online as “retatrutide” are not equivalent to Lilly clinical-trial medicine.
Side effects: what changed in the newest Reta data?
The newest Phase 3 results give a much clearer picture of retatrutide tolerability.
| TRIUMPH-1 adverse event | Reta 4 mg | Reta 9 mg | Reta 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhoea | 25.2% | 34.1% | 32.0% | 13.5% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Dysesthesia | 5.1% | 12.3% | 12.5% | 0.9% |
| Stopped due to adverse events | 4.1% | 6.9% | 11.3% | 4.9% |
For tirzepatide in SURMOUNT-1, gastrointestinal events were also the most common side effects and were generally mild to moderate, especially during dose escalation.
See also: GLP-1 Side Effects Explained and Retatrutide Side Effects.
What are people saying anecdotally?
Online experiences are useful for spotting themes, but they are not clinical evidence. With retatrutide especially, many online users are discussing unapproved products whose identity, concentration and purity cannot be assumed.
Several people switching from tirzepatide to retatrutide report that food noise or hunger returns, particularly early after the switch. That does not mean Reta is less effective overall, but the subjective appetite effect may feel different.
Example discussion on Reddit ↗A common reason discussed online is stalled weight loss after months on tirzepatide. Some users report renewed progress after changing compounds, while others report little effect or even regain.
Example switch discussion ↗Some users describe excellent results on retatrutide; others say tirzepatide controlled hunger better. The variation is exactly why anecdotes should not be used to predict an individual’s outcome.
Example mixed experience ↗Unlike Mounjaro, retatrutide is not an approved retail medicine. That means online anecdotes may involve products from different suppliers, concentrations or quality standards — a major confounder when comparing experiences.
View Peptide Hub test-result resources →So which is better for weight loss?
On efficacy alone: Retatrutide currently leads
If the question is simply “which drug has produced the larger average weight-loss number in a Phase 3 obesity trial?”, the answer is retatrutide.
TRIUMPH-1’s 28.3% average reduction at 80 weeks is materially above the 20.9% average reduction reported with tirzepatide 15 mg at 72 weeks in SURMOUNT-1.
On proven, available treatment today: Mounjaro is in a different category
Mounjaro is TGA-approved in Australia for chronic weight management and has a mature evidence base. Retatrutide is still investigational. So “better trial efficacy” and “better treatment choice today” are not the same question.
The cleanest conclusion is: retatrutide currently looks more powerful for average total weight loss, while tirzepatide has the advantage of regulatory approval, longer-term evidence and established clinical use.
Related Peptide Hub Australia guides
Sources
May 2026 topline and adverse-event data for retatrutide.
July 2026 Phase 3 topline results.
Pivotal 72-week tirzepatide obesity trial.
176-week data in participants with obesity and prediabetes.
Australian approval status for tirzepatide.
Current investigational and regulatory status.
Mounjaro vs Retatrutide FAQ
Is Retatrutide better than Mounjaro for weight loss?
Retatrutide has produced a larger average weight-loss result in separate Phase 3 trials: 28.3% at 80 weeks with 12 mg in TRIUMPH-1 versus 20.9% at 72 weeks with tirzepatide 15 mg in SURMOUNT-1. However, there has not yet been a direct head-to-head trial, so superiority has not been formally proven.
Is Retatrutide the same as Mounjaro?
No. Mounjaro contains tirzepatide and targets GIP and GLP-1 receptors. Retatrutide targets GIP, GLP-1 and glucagon receptors.
Is Retatrutide approved in Australia?
No. Retatrutide remains investigational and is not TGA-approved. Lilly states it is legally available through its clinical trials while development continues.
Is Mounjaro approved for weight loss in Australia?
Yes. The TGA has approved Mounjaro (tirzepatide) for chronic weight management in eligible adults, in addition to its type 2 diabetes indication.
How much weight did people lose on Retatrutide in Phase 3?
In TRIUMPH-1, the 12 mg retatrutide group achieved 28.3% average weight reduction at 80 weeks under the efficacy estimand. A selected extension subgroup reached 30.3% at 104 weeks.
How much weight did people lose on Mounjaro / tirzepatide?
In SURMOUNT-1, average weight reduction at 72 weeks was 15.0% with 5 mg, 19.5% with 10 mg and 20.9% with 15 mg tirzepatide.
Does Retatrutide suppress appetite more than Mounjaro?
Not necessarily. Anecdotally, some people report stronger appetite suppression and less food noise with tirzepatide, even though retatrutide has produced greater average weight reduction in clinical trials. Individual experience varies.
Why might Retatrutide cause more weight loss?
Retatrutide adds glucagon receptor activity to GIP and GLP-1 receptor activity. Researchers believe this third pathway may contribute additional metabolic and energy-expenditure effects.