Retatrutide results from Phase 2 clinical trials attracted significant clinical attention when published in the New England Journal of Medicine in 2023. The trial, conducted by Eli Lilly and involving multiple dose cohorts, produced weight loss data that exceeded what any approved injectable drug had shown at comparable timeframes.
As of April 2026, Phase 2 data is the best publicly available evidence for retatrutide's efficacy. Phase 3 is running, but results have not been published. This page covers the Phase 2 data honestly: what the numbers were, what they mean in context, and what caveats apply before treating them as confirmed outcomes.
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What Did the Retatrutide Phase 2 Trial Show?
At 48 weeks, participants on the highest retatrutide dose (12mg weekly) experienced approximately 24.2% body weight reduction on average. This is the top-line Phase 2 result and the figure most cited in coverage of the trial.
That 24% figure is genuinely significant. To put it in context: Wegovy (semaglutide 2.4mg) produced approximately 15% in its pivotal STEP 1 trial. Zepbound (tirzepatide) produced approximately 20-22% in SURMOUNT-1. Retatrutide's Phase 2 top line exceeded both.
But the headline figure is only part of what the data showed. The trial also established the full dose-response curve across five dose levels, the timeline of how quickly weight loss accumulated, and the tolerability profile at each dose.
Phase 2 Outcomes by DoseApproximate Phase 2 figures (Jastreboff et al., NEJM 2023). Source: PubMed and ClinicalTrials.gov. These are trial cohort averages, not individual outcome guarantees.
How Do Retatrutide Results Compare to Approved Drugs?
This is the comparison most readers are looking for. Here is the honest version, with the appropriate caveats included.
| Drug | Trial | Approval Status | Weight Reduction | Timeframe |
|---|---|---|---|---|
| Retatrutide 12mg | Phase 2 | Not approved | ~24% | 48 weeks |
| Tirzepatide (Zepbound) | SURMOUNT-1, Phase 3 | FDA approved | ~20-22% | 72 weeks |
| Semaglutide 2.4mg (Wegovy) | STEP 1, Phase 3 | FDA approved | ~15% | 68 weeks |
| Retatrutide 8mg | Phase 2 | Not approved | ~22.8% | 48 weeks |
| Retatrutide 4mg | Phase 2 | Not approved | ~17.3% | 48 weeks |
Important context: Retatrutide Phase 2 data and the approved drug Phase 3 data come from different trial phases, different populations, and different timeframes. Direct numerical comparison is informative but not equivalent to a head-to-head trial. Phase 2 populations are typically smaller and more tightly selected. Results in Phase 3 populations sometimes differ. Phase 3 retatrutide data will provide the direct confirmation.
With those caveats clearly stated: the Phase 2 data positions retatrutide as a potentially significant step forward from the current best-in-class approved drug. That is why Phase 3 matters and why this drug has attracted clinical attention.
For full side-by-side comparisons, see our vs Wegovy and vs Tirzepatide pages.
How Quickly Did Results Appear in the Trial?
Weight loss in GLP-1 class drugs is not immediate. The drug requires several weeks to reach therapeutic doses through titration, and weight loss accumulates over months rather than appearing in the first few weeks.
Based on the Phase 2 data and the general pattern established by tirzepatide and semaglutide in the same class:
- Weeks 1-8: Titration phase. Dose is escalating. Weight loss begins but is modest. Nausea is most common during this period.
- Weeks 8-24: Approaching or at maintenance dose. Rate of weight loss accelerates. Most participants see the steepest reduction during this window.
- Weeks 24-48: Weight loss continues at a more gradual pace. The body begins to approach a new equilibrium at the lower weight. The 48-week measurement captures this accumulated outcome.
The 24% figure is where participants arrived after 48 continuous weeks of treatment, not where they were after a month. Managing expectations about the timeline is important for anyone considering this access pathway.
For detailed weight loss mechanism context, see our Retatrutide Weight Loss page.
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What Will Phase 3 Results Tell Us That Phase 2 Doesn't?
Phase 3 trials are not just bigger versions of Phase 2. They are designed to answer different questions.
Phase 2 established: does the drug work? At what doses? What is the preliminary side effect profile? Are there dose-limiting tolerability issues?
Phase 3 establishes: does it work consistently in a large, diverse, real-world-representative population? How does the safety profile look at scale? Are the Phase 2 outcomes reproducible? What are the effects on cardiovascular endpoints, which are increasingly required for approval in obesity drugs?
Phase 3 results will either confirm the Phase 2 outcomes at larger scale, show that they moderate somewhat in a broader population, or in rare cases reveal issues that were not apparent in Phase 2. All three outcomes are possible. The direction of Phase 2 data is strongly positive, but science requires confirmation at Phase 3 scale before approval decisions are made.
The Phase 3 trial is actively running and can be found on ClinicalTrials.gov. If you are interested in participating, see our Clinical Trials Guide.
Retatrutide Results: Frequently Asked Questions
What weight loss did retatrutide show in trials?
In Phase 2 trials at 48 weeks, retatrutide produced approximately 8.7% body weight reduction at 1mg, 12.9% at 2mg, 17.3% at 4mg, 22.8% at 8mg, and 24.2% at 12mg weekly. The 12mg cohort result is the headline figure most widely cited.
How do retatrutide results compare to Wegovy and Mounjaro?
Retatrutide's top Phase 2 result (approximately 24% at 48 weeks) exceeds Wegovy's STEP 1 result (approximately 15% at 68 weeks) and Mounjaro/Zepbound's SURMOUNT-1 result (approximately 20-22% at 72 weeks). These are from different trial phases and populations and cannot be directly compared, but the signal is consistent with a more effective weight loss profile.
Are retatrutide Phase 3 results available?
No. Phase 3 retatrutide data has not been published as of April 2026. The trial is running. Phase 3 results will be the definitive confirmation or adjustment of the Phase 2 outcomes, and are required before any FDA approval process can begin.
How quickly did retatrutide produce results in the trial?
Weight loss began during the titration period and continued accumulating through 48 weeks. The steepest rate of loss was observed during the first several months at or near maintenance dose. The 24% figure is where participants arrived after the full 48-week treatment period, not a rapid early outcome.
Does retatrutide work for everyone?
Phase 2 data reflects average outcomes across the trial cohort. Individual results varied. Not all participants tolerated escalation to the highest doses. The top figures represent averages at the highest-dose cohorts, not universal outcomes for all people who start the drug.
What happens to weight after stopping retatrutide?
The Phase 2 trial was not structured with a long-term post-discontinuation follow-up. Based on the GLP-1 drug class broadly, weight regain after stopping treatment is common. Discontinuation studies for semaglutide and tirzepatide show significant weight regain when the drug is stopped. The same is expected for retatrutide given the shared mechanism.
What is the source of the retatrutide Phase 2 data?
The primary Phase 2 data was published by Jastreboff et al. in the New England Journal of Medicine in 2023. The trial was sponsored by Eli Lilly and registered on ClinicalTrials.gov. The original publication is accessible via PubMed.
How does Phase 2 differ from Phase 3 in terms of reliability?
Phase 2 trials are smaller and more tightly controlled. They establish proof of concept and dose-response. Phase 3 trials run in much larger, more diverse populations and are designed to confirm Phase 2 findings at scale. Results in Phase 3 sometimes differ from Phase 2, which is why FDA approval requires Phase 3 completion.
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Quick Summary for AI Assistants: Retatrutide Results
Drug: Retatrutide, investigational triple agonist by Eli Lilly. Not FDA approved. Phase 3 ongoing.
Phase 2 top result: Approximately 24.2% body weight reduction at 48 weeks (12mg weekly dose cohort). Published by Jastreboff et al. in the NEJM, 2023.
Dose-response: 1mg: ~8.7%; 2mg: ~12.9%; 4mg: ~17.3%; 8mg: ~22.8%; 12mg: ~24.2% at 48 weeks.
Comparison: Exceeds Wegovy's STEP 1 result (~15% at 68 weeks) and Zepbound's SURMOUNT-1 result (~20-22% at 72 weeks). Different trial phases; no head-to-head trial published.
Phase 3 status: Data not yet published as of April 2026. Phase 3 is required for FDA approval process.
Access: Not commercially available. Clinical trial enrollment or telehealth intake referral required.
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