Retatrutide Results: How Much Weight Loss Do Studies Show?

Retatrutide (LY3437943) is an investigational triple agonist that has produced some of the largest weight-loss figures reported for any obesity drug. This guide sticks to what the published trials and official trial readouts show with the sources, and flags clearly where the widely repeated numbers are not yet verifiable.

Retatrutide is not an approved medication. It remains investigational and is being studied in clinical trials. Nothing here is medical advice.

The Phase 2 obesity trial: the headline numbers

The most-cited evidence is the Phase 2 obesity trial published in the New England Journal of Medicine in 2023 (Jastreboff et al.). It enrolled 338 adults with obesity and ran for 48 weeks. Average (least-squares mean) body-weight change by dose:

So the commonly quoted "up to ~24% at 48 weeks" figure is accurate, it's the 12 mg group average. Weight loss was already well underway by the halfway point (about −17.5% at the 12 mg dose by 24 weeks) and had not plateaued by week 48, which is part of why the drug drew so much attention.

The proportion of participants hitting weight-loss milestones at 48 weeks was also high at the upper doses:

We're deliberately not listing ≥20%, ≥25% or ≥30% responder percentages: those figures circulate widely but we couldn't confirm exact values in the openly available trial report, so we're leaving them out rather than publish numbers we can't source.

Diabetes and liver-fat trials

Retatrutide has been studied beyond simple weight loss.

In a separate Phase 2 trial in people with type 2 diabetes published in The Lancet (Rosenstock et al., 2023), the primary glycemic readout at 24 weeks showed least-squares mean HbA1c reductions of about −2.0 percentage points on the 12 mg retatrutide escalation arm (published figure −2.02%), versus essentially no change on placebo and about −1.4% on dulaglutide 1.5 mg. Higher retatrutide doses also produced substantial weight loss (on the order of ~17% at 12 mg over the longer ~36-week follow-up in public summaries).

A dedicated Phase 2a trial in fatty liver disease (MASLD), published in Nature Medicine in 2024 (Sanyal et al.), reported dramatic reductions in liver fat: at 48 weeks, liver fat content fell by about 86% at the 12 mg dose, and 93% of participants on 12 mg reached normal liver fat levels (under 5%), versus none on placebo. These are striking, though it was a small study (98 participants).

Phase 3 topline data: promising, but not yet peer-reviewed

Retatrutide's Phase 3 program (TRIUMPH) began reporting in late 2025 and 2026. Two important points before the numbers:

1. These are company topline announcements, not peer-reviewed publications. The full data and independent review aren't published yet.
2. The first readouts come from specific populations, so they aren't a clean stand-in for a general-obesity result.

With that framing, Lilly's December 2025 topline announcement for TRIUMPH-4 , a trial in adults with obesity and knee osteoarthritis: reported average weight loss of about 28.7% at the 12 mg dose over 68 weeks (roughly 71 pounds), with meaningful reductions in knee-osteoarthritis pain. A subsequent May 2026 topline announcement for the registrational obesity trial TRIUMPH-1 reported average loss of about 28.3% at 12 mg over 80 weeks (company press materials; peer-reviewed full paper may lag). Several other TRIUMPH trials had different designs and readouts, treat uncited numbers as speculation until you can match them to a primary source.

How to read percent weight loss without fooling yourself

A 24% average at 48 weeks is a group least-squares mean, not a promise that every individual loses 24%. Distributions matter: some lose more, some less, some discontinue. Responder tables (5%/10%/15% thresholds) show how common clinically meaningful loss was — still under trial conditions.

Also separate:

1. On-treatment trial results under protocol titration
2. Real-world adherence, diet quality and supply
3. Gray-market product results that may not be retatrutide at all

Time course (Phase 2 pattern)

The Phase 2 obesity program did not wait until week 48 to show movement:

Checkpoint	What the public figures support	Takeaway
Early weeks	Appetite and intake changes begin as doses escalate	Not a full “final result” window
~24 weeks	Higher-dose arms already near the high teens % average loss	Loss is substantial before 48 weeks
48 weeks	~24% average at 12 mg; still no clear plateau in that trial	Why longer Phase 3 horizons matter

Titration structure (not a DIY schedule): retatrutide dosage.

Body composition honesty

Scale weight is the headline endpoint. It does not automatically mean “only fat.” Large losses on incretin-class drugs can include lean mass if nutrition and resistance training are ignored. Class context: GLP-1 muscle loss.

If a marketing post promises “spot fat reduction” or “no muscle loss,” demand the measurement method (DXA vs scale vs guesswork) and the actual paper — not a screenshot.

Cross-trial comparison table (approximate public figures)

Program	Approximate average weight change	Horizon	Caveat
Semaglutide STEP 1	~15% (2.4 mg weekly arm)	68 weeks	Approved product pathway (Wegovy)
Tirzepatide SURMOUNT-1	Up to ~21% at highest dose	72 weeks	Approved as Zepbound
Retatrutide Phase 2 obesity	~24% at 12 mg	48 weeks	Shorter horizon; investigational
Retatrutide Phase 3 topline (examples)	TRIUMPH-4 ~28.7% at 12 mg; TRIUMPH-1 ~28.3% at 12 mg	68 weeks (TRIUMPH-4); 80 weeks (TRIUMPH-1)	Company toplines; match figures to the specific trial before citing

Use tirzepatide vs retatrutide for the decision framing, not just the percent column.

Secondary outcomes that matter beyond the scale

• Glycemic markers in diabetes Phase 2 (HbA1c reductions at higher doses)
• Liver fat reductions in MASLD Phase 2a
• Patient-reported outcomes (e.g. pain in TRIUMPH-4 osteoarthritis population) when disclosed in topline releases

Obesity medicine is moving toward multi-morbidity endpoints. Weight % is the headline; it is not the only endpoint regulators and clinicians will weigh.

What would change these numbers

• Different maintenance dose
• Different escalation speed (tolerability ? adherence)
• Higher baseline BMI or more diabetes in the sample
• Concurrent lifestyle intensity
• Discontinuation and missing-data handling in the analysis

That is another reason DIY "I should see 24% in 6 months" expectations fail.

Why "before and after" photos deserve skepticism

Searches for retatrutide results surface a lot of user-posted before/after photos. Treat them cautiously:

• Trial averages reflect controlled dosing, supervised escalation, and lifestyle support that random online users may not replicate.
• Products sold online as "retatrutide" are not verified to be the same molecule, dose, or purity as the trial drug. See tirzepatide vs retatrutide for why the research-grade vs approved-medicine distinction matters.
• Photos can't show side effects, muscle loss, or whether the loss was sustained.

The trustworthy numbers are the trial figures above, not anecdotes.

What happens if you stop?

This is where the evidence runs out for retatrutide specifically: there is no published retatrutide discontinuation or maintenance study. What we can say comes from the closely related drug tirzepatide. In the SURMOUNT-4 trial (JAMA, 2024), people who switched from tirzepatide to placebo regained a large share of their lost weight over the following year, while those who continued kept losing. GLP-1-class drugs broadly show significant regain after stopping.

The reasonable expectation, then, is that retatrutide's results would also depend on continued treatment and lifestyle change, but for retatrutide itself, that's an inference from related drugs, not a proven finding.

The bottom line

Retatrutide's trial results are genuinely among the strongest reported in obesity medicine: about 24% average weight loss at 48 weeks in Phase 2, with higher Phase 3 topline figures and large metabolic and liver-fat improvements. But "investigational" still applies, the Phase 3 data isn't peer-reviewed, the durability question is unanswered for this specific drug, and it isn't approved or available as a prescription product.

For how the trials structured dosing, see retatrutide dosing in clinical trials; for what the drug does mechanistically, see how retatrutide works; and for the safety picture, see retatrutide side effects.

References

1. Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. New England Journal of Medicine, 2023.

2. Rosenstock J, Frias J, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, phase 2 trial. The Lancet, 2023.

3. Sanyal AJ, Kaplan LM, Frias JP, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature Medicine, 2024.

4. Eli Lilly and Company. Lilly triple agonist retatrutide Phase 3 TRIUMPH-4 topline. December 2025.

5. Eli Lilly and Company. TRIUMPH-1 Phase 3 topline results. May 2026.

6. Aronne LJ, Horn DB, le Roux CW, et al. Continued tirzepatide treatment vs withdrawal on weight maintenance (SURMOUNT-4). JAMA, 2024.