Retatrutide Weight Loss: What the Research Shows
If you follow obesity medicine research, you have probably heard the excitement around retatrutide. The Phase 2 data published in the New England Journal of Medicine drew headlines for a reason: at th
In this article
*Retatrutide is an investigational drug that is not FDA-approved and is not currently available through Prescriva or any commercial channel. This article is for educational and informational purposes only and does not constitute medical advice. Consult your licensed healthcare provider before starting any weight loss treatment.*
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If you follow obesity medicine research, you have probably heard the excitement around retatrutide. The Phase 2 data published in the New England Journal of Medicine drew headlines for a reason: at the highest dose studied, participants lost an average of 24% of their body weight over 48 weeks.
That number is striking. It is higher than anything seen in pivotal trials of semaglutide or tirzepatide. But there is important context, and a lot of nuance, that gets lost in the headlines.
This article walks through what the research actually shows, why retatrutide's mechanism is different from other injectable weight loss medications, what the trial data does and does not tell us, and where things stand as the drug moves into Phase 3 trials.
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What Is Retatrutide?
Retatrutide (also known by the development code LY3437943) is a once-weekly injectable peptide developed by Eli Lilly. Like semaglutide and tirzepatide, it activates the GLP-1 receptor. But retatrutide goes further.
It is a triple agonist: it activates three hormone receptors simultaneously.
- GLP-1 receptor (glucagon-like peptide-1): Reduces appetite, slows gastric emptying, and improves insulin sensitivity. This is the same receptor targeted by semaglutide, and one of two targeted by tirzepatide.
- GIP receptor (glucose-dependent insulinotropic polypeptide): Potentiates insulin secretion and contributes to appetite regulation. This is the second receptor targeted by tirzepatide.
- Glucagon receptor: This is where retatrutide is unique among approved and near-approved medications. Glucagon is typically associated with raising blood sugar, but glucagon receptor activation in the context of caloric restriction appears to increase energy expenditure, promote fat breakdown, and reduce liver fat.
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Phase 2 Results: What the NEJM Trial Found
The pivotal Phase 2 data comes from a double-blind, placebo-controlled trial published in the New England Journal of Medicine in August 2023. ([PMID: 37366315](https://pubmed.ncbi.nlm.nih.gov/37366315/))
The trial enrolled 338 adults with a body mass index of 27 or higher (without type 2 diabetes) and randomized them to receive weekly injections of retatrutide at one of five doses (1mg, 4mg, 8mg, or 12mg) or placebo over 48 weeks.
The results at 48 weeks:
| Dose | Average Body Weight Change |
|---|---|
| Placebo | -2.1% |
| 1 mg | -8.7% |
| 4 mg | -17.3% |
| 8 mg | -22.8% |
| 12 mg | -24.2% |
A companion trial in adults with type 2 diabetes, published in The Lancet, confirmed weight loss benefits in a diabetic population as well, with an average reduction of up to 16.9% at the highest dose tested. ([PMID: 37385280](https://pubmed.ncbi.nlm.nih.gov/37385280/))
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Body Composition: Where Is the Weight Coming From?
Total weight loss numbers matter, but researchers also want to know what kind of weight is being lost. A 2025 body composition substudy published in Lancet Diabetes and Endocrinology examined DXA (dual-energy X-ray absorptiometry) scans and MRI data from a subset of participants in the Phase 2 type 2 diabetes trial. ([PMID: 40609566](https://pubmed.ncbi.nlm.nih.gov/40609566/))
The substudy found that retatrutide produced significant reductions in both visceral adipose tissue (the metabolically dangerous fat surrounding organs) and subcutaneous adipose tissue (the fat layer beneath the skin). Lean muscle mass was largely preserved relative to the proportion of total weight lost, which is consistent with findings from semaglutide and tirzepatide trials.
Visceral fat reduction is particularly meaningful from a cardiovascular and metabolic risk standpoint. Visceral fat is more strongly associated with insulin resistance, inflammation, and cardiovascular disease than total body weight alone.
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How Does Retatrutide Compare to Semaglutide and Tirzepatide?
A Bayesian network meta-analysis published in the journal Obesity in 2025 pooled data from trials of GLP-1 receptor agonists, dual agonists, and retatrutide to produce comparative weight loss estimates. ([PMID: 40685589](https://pubmed.ncbi.nlm.nih.gov/40685589/))
In this analysis, retatrutide at the highest tested doses ranked above both semaglutide and tirzepatide for average weight reduction. A systematic review and meta-analysis published in Expert Review of Clinical Pharmacology similarly concluded that retatrutide demonstrated "superior" weight loss compared to single and dual agonists in the Phase 2 data, while noting that the comparative trials are indirect and that head-to-head data remains limited. ([PMID: 39817343](https://pubmed.ncbi.nlm.nih.gov/39817343/))
There are important caveats to keep in mind when reading these comparisons:
The dose matters. The 12mg retatrutide dose that produced 24% weight loss is the highest studied dose in a Phase 2 trial with carefully selected participants. Real-world outcomes across a broader population may differ.
Phase 2 populations are small. The core obesity Phase 2 trial enrolled 338 participants. The tirzepatide SURMOUNT-1 trial enrolled over 2,500. Larger Phase 3 trials test durability, safety signals, and outcomes across a more representative population.
Indirect comparisons have limits. Network meta-analyses are valuable tools for synthesizing data, but they are not the same as a head-to-head randomized controlled trial. The populations, dosing regimens, trial durations, and baseline characteristics across trials differ in ways that affect the estimates.
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Side Effects and Tolerability
Retatrutide's side effect profile in Phase 2 trials was broadly consistent with the GLP-1 class. The most commonly reported adverse effects were gastrointestinal: nausea, vomiting, diarrhea, constipation, and decreased appetite. These effects were more frequent at higher doses and tended to be mild to moderate in severity.
Serious adverse events occurred at similar rates between the retatrutide and placebo groups. There was no signal of increased heart rate at the level seen with some other GLP-1 receptor agonists. The hypoglycemia risk was low in the non-diabetic obesity trial, consistent with the glucose-dependent mechanism of GLP-1 and GIP receptor agonism.
A phase 2 study examining eating behaviors and appetite found that retatrutide reduced hunger, increased satiety, and produced changes in eating attitudes consistent with its effects on body weight. ([PMID: 40916752](https://pubmed.ncbi.nlm.nih.gov/40916752/)) Participants reported eating less at meals and feeling less preoccupied with food, which mirrors qualitative reports from semaglutide and tirzepatide users.
One area under active study is the glucagon component's effect on heart rate. Glucagon receptor activation has been associated with mild increases in heart rate in some studies. The clinical significance of this in the context of retatrutide treatment is being monitored in ongoing trials.
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Where Are We Now: The TRIUMPH Phase 3 Trials
The Phase 2 results were compelling enough to advance retatrutide into a registrational Phase 3 program called TRIUMPH (TRIple hormone agonism for the treatment of OBesity and its coMorbiditieS with retatrUtide in PHase 3 trials). The TRIUMPH program was designed to evaluate retatrutide across multiple conditions, including:
- Obesity without type 2 diabetes
- Obesity with type 2 diabetes
- Obstructive sleep apnea
- Knee osteoarthritis
As of the date of this article, Phase 3 results have not been published and retatrutide has not received FDA approval. Eli Lilly has not announced a commercial launch timeline.
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What This Means If You Are Considering Weight Loss Treatment
Retatrutide is not available for prescription today. It is an investigational compound that remains in clinical trials, and it will need to complete Phase 3 trials, pass FDA review, and enter the commercial market before it is accessible to patients outside of a research setting.
The Phase 2 results are genuinely exciting for obesity medicine. A drug that produces 24% average body weight loss would represent a meaningful advance over current options. But Phase 2 results do not always replicate in larger Phase 3 populations, and the long-term safety and durability of retatrutide effects remain to be established.
If you are looking for treatment today, two well-studied, evidence-based options are available. [Compounded semaglutide](/resources/compounded-semaglutide-what-it-is) is a GLP-1 receptor agonist with a long clinical track record, including the landmark STEP trial series showing average weight loss of 14.9% over 68 weeks. [Compounded tirzepatide](/resources/compounded-tirzepatide-guide) is a dual GLP-1 and GIP receptor agonist with Phase 3 data showing average weight loss of 20-22% at the highest studied dose.
Both are available through licensed telehealth providers today. Retatrutide, when it reaches the market, will likely take its place alongside them as another option in a maturing field.
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A Note on Compounded Medications
Compounded semaglutide and compounded tirzepatide referenced throughout this article are not FDA-approved drug products. They are prepared by licensed compounding pharmacies under Section 503A of the Federal Food, Drug, and Cosmetic Act for individual patients with valid prescriptions. Compounded medications are distinct from the branded FDA-approved versions and have not undergone the same FDA approval process for safety, efficacy, and manufacturing quality.
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The Bottom Line
Retatrutide's Phase 2 data is among the most impressive seen in obesity pharmacotherapy. The triple agonist mechanism, adding glucagon receptor activation to the now-established GLP-1 and GIP combination, opens a potentially new chapter in how researchers think about metabolic treatment.
The key questions that Phase 3 must answer: Does the effect hold across a broader, more diverse population? What does long-term safety look like over two or more years? Does the weight loss persist when treatment continues? What happens to cardiometabolic risk markers over time?
Those results, when they arrive, will tell a more complete story. For now, the Phase 2 data establishes retatrutide as a serious candidate in the next generation of obesity medicine.
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*This article is for informational purposes only and does not constitute medical advice. Retatrutide is an investigational drug that is not FDA-approved. Compounded semaglutide and compounded tirzepatide are not FDA-approved. Results in referenced clinical trials were obtained in specific study populations under controlled conditions; individual results vary. Always consult your licensed healthcare provider before starting, stopping, or adjusting any medication. Care at Prescriva is delivered by independently licensed providers, not by Prescriva LLC, doing business as Prescriva, which is a management services organization.*
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