Reta is the nickname for retatrutide, an experimental weight loss drug developed by Eli Lilly. In the Phase 3 TRIUMPH-1 trial, participants receiving the highest tested dose lost an average of 28.3% of their starting body weight over 80 weeks in the efficacy analysis, equivalent to 70.3 pounds.
The peer-reviewed treatment-regimen analysis reported 25.0% at the same dose. The smaller figure accounts for treatment discontinuation and other events under the trial methodology, giving a more realistic estimate of the overall treatment response.
Unlike Ozempic and Wegovy, retatrutide activates three hormone receptors involved in appetite and metabolism. More receptors do not automatically mean better results. Semaglutide achieved substantial weight loss in STEP trials with one pathway, and tirzepatide achieved reductions exceeding 20% in SURMOUNT trials with two. Neither requires glucagon activation.
Retatrutide is not FDA-approved. We previously examined Eli Lilly’s development and early-access plans. The FDA has warned companies against marketing unapproved retatrutide products, and vials advertised online as Reta are not equivalent to the medication supplied to clinical trials.
The 28.3% result describes weight loss during treatment. What happens after patients stop injections remains an unanswered question.
How Effective Is Reta for Weight Loss?
Retatrutide is designed as a once-weekly injection. It activates three hormone receptors involved in appetite, blood glucose and energy metabolism.
- GLP-1 helps regulate appetite, food intake and insulin release.
- GIP contributes to insulin signaling and metabolic regulation.
- Glucagon influences glucose production and energy metabolism.
Glucagon is the additional component separating retatrutide from tirzepatide. Yet no published analysis assigns a specific share of the reported 28.3% weight reduction to glucagon receptor activation.
The uncertainty is substantial. Researchers would need a study isolating glucagon activity, or a direct comparison against GLP-1/GIP treatment at comparable tolerability, to establish how much weight loss the third pathway adds.
Glucagon can also stimulate glucose production. Combining it with GLP-1 and GIP activity is intended to influence both appetite and energy metabolism, but the complete contribution of each pathway remains under investigation.
Continuing treatment is another concern. The TRIUMPH-2 Lancet publication, DOI 10.1016/S0140-6736(26)01861-1, reports permanent treatment discontinuation due to adverse events or death in 12% of participants receiving 9 mg, compared with 5% receiving placebo. Both figures use the same trial placebo group, as reported in its safety findings.
One in eight stopped at 9 mg. The result puts a practical limit on how clinicians should interpret the impressive weight-loss averages.
How Much Weight Can You Lose on Retatrutide?
At 12 mg, TRIUMPH-1 reported 28.3% average weight loss in the efficacy analysis and 25.0% in the treatment-regimen analysis after 80 weeks. The study enrolled adults with obesity who did not have diabetes.
Participants received weekly doses of 4 mg, 9 mg or 12 mg, or placebo. The highest dose produced the largest average reduction.
| TRIUMPH-1 Finding | Reported Result |
|---|---|
| Study duration | 80 weeks |
| Study population | Adults with obesity, without diabetes |
| Highest dose | 12 mg weekly |
| Average weight loss, efficacy analysis | 28.3% |
| Average weight loss, treatment-regimen analysis | 25.0% |
| Average loss in pounds, efficacy analysis | 70.3 pounds |
| Participants losing at least 30%, efficacy analysis | 45.3% |
Source: Eli Lilly TRIUMPH-1 efficacy results, May 21, 2026, efficacy and responder tables. TRIUMPH-1 also has a peer-reviewed NEJM publication, cited in the introduction. The 28.3%, 70.3-pound and 45.3% figures use the company-reported efficacy analysis.
The 3.3-percentage-point gap comes from two statistical approaches. It does not mean that 3.3% of patients stopped treatment. The treatment-regimen analysis accounts for discontinuation and other events when estimating average weight change.
Among participants assigned to 12 mg, 45.3% lost at least 30% of their starting weight, compared with 0.5% on placebo. The figures come from the company efficacy analysis rather than the treatment-regimen estimate.
Selected participants continued into a 104-week extension. Among those with a starting BMI of at least 35, the highest-dose group reached an average reduction of 30.3%.
The Eli Lilly extension update reported 85 pounds of average weight loss in that subgroup. Across the extension, 532 participants entered the additional treatment period.
Everyone in the extension had already completed the first 80 weeks and remained eligible to continue. The result therefore describes a selected population, not everyone initially randomized.
Withdrawal studies of approved medicines offer a warning. In the STEP-1 semaglutide extension, participants regained about two-thirds of their previous weight loss within a year of stopping treatment.
The SURMOUNT-4 tirzepatide trial recorded an average 14% weight regain over 52 weeks among participants switched to placebo.
Retatrutide has no equivalent published randomized withdrawal result. Its 104-week extension measured continued dosing, not weight maintenance after stopping.
Retatrutide Also Produced Major Weight Loss in People With Type 2 Diabetes
TRIUMPH-2 enrolled 1,152 adults with overweight or obesity and type 2 diabetes. The study addressed a population that generally records smaller weight reductions in obesity medication trials.
The published treatment-regimen results after 80 weeks were as follows.
| Weekly Treatment | Average Weight Loss |
|---|---|
| Retatrutide 4 mg | 11.9% |
| Retatrutide 9 mg | 16.8% |
| Retatrutide 12 mg | 18.8% |
| Placebo | 5.1% |
Source: TRIUMPH-2, The Lancet, treatment-regimen and metabolic-outcome analyses.
At 12 mg, the estimated weight reduction was 13.8 percentage points greater than placebo, with a 95% confidence interval of 11.8 to 15.8 percentage points.
The published TRIUMPH-2 results, PMID 42810372, reported that 47% of participants receiving 12 mg lost at least 20% of their starting weight, against 6% on placebo. At the 25% threshold, the figures were 31% and 3%.
Blood sugar improved as well. In the published Lancet metabolic analysis, average HbA1c fell by 1.45 percentage points with 12 mg retatrutide, compared with 0.45 points on placebo. At that dose, 72% reached an HbA1c of 6.5% or lower, against 29% receiving placebo.
The combined findings give clinicians two outcomes to consider. Weight reduction was greater than placebo, and HbA1c improved. The safety and discontinuation rates determine how those benefits fit into treatment decisions.
Why the Exact Efficacy Numbers Depend on the Analysis
Video: Dr. Kevin Joseph, DO, discusses retatrutide and the GLP-1, GIP and glucagon pathways. His commentary is published through his YouTube channel, not as an official TRIUMPH trial presentation. The clinical figures in this article come from the published research.
TRIUMPH-2 produced two widely reported estimates at its highest dose. Eli Lilly announced 20.8% average weight loss in July, whereas the peer-reviewed treatment-regimen analysis reported 18.8%.
The July 23 company announcement used an efficacy analysis with assumptions about continued treatment. The journal publication accounted for discontinuation and other interventions under its treatment-regimen methodology.
For treatment-regimen comparisons, 18.8% is the relevant TRIUMPH-2 figure. The 20.8% estimate is valid when clearly identified as the efficacy analysis.
TRIUMPH-1 presents the same reporting issue at 12 mg, with 28.3% and 25.0% from separate analyses. Mixing those methods gives readers an unreliable drug comparison.
Differences Between Ozempic, Zepbound and Reta
Ozempic and Wegovy contain semaglutide, which activates GLP-1 receptors. Mounjaro and Zepbound contain tirzepatide, activating GLP-1 and GIP receptors. Retatrutide adds glucagon receptor activity.
| Medication | Active Ingredient | Receptors Targeted | U.S. Regulatory Position |
|---|---|---|---|
| Ozempic | Semaglutide | GLP-1 | FDA-approved |
| Wegovy | Semaglutide | GLP-1 | FDA-approved |
| Mounjaro | Tirzepatide | GLP-1 and GIP | FDA-approved |
| Zepbound | Tirzepatide | GLP-1 and GIP | FDA-approved |
| Retatrutide | Retatrutide | GLP-1, GIP and glucagon | Investigational |
We have previously examined GLP-1 medication use among American women, including the expanding use of treatments already available.
Neither TRIUMPH-1 nor TRIUMPH-2 directly compared retatrutide with semaglutide or tirzepatide. A head-to-head trial measuring weight loss alongside adverse effects and discontinuation would provide a stronger comparison.
Until those results exist, the 28.3% efficacy estimate cannot establish that retatrutide beats Zepbound in equivalent patients.
What Are the Side Effects of Retatrutide?
Diarrhea affected 27% to 34% of participants receiving retatrutide in TRIUMPH-2, compared with 13% on placebo. Nausea ranged from 14% to 28%, against 8% receiving placebo.
The published trial provides enough information to compare adverse events by dose rather than relying on pooled ranges.
| Adverse Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Diarrhea | 27% | 34% | 34% | 13% |
| Nausea | 14% | 21% | 28% | 8% |
| Hypotension | 1% | 5% | 6% | Less than 1% |
| Dysesthesia | 4% | 6% | 7% | 1% |
| Permanent discontinuation due to adverse events or death | 4% | 12% | 8% | 5% |
Source: TRIUMPH-2, The Lancet, Findings section and adverse-event analysis. Percentages are rounded from individual trial arms. The placebo column represents the trial’s shared placebo group.
The dose-specific results show that nausea and dysesthesia increased across the tested doses. Diarrhea remained near 34% at both 9 mg and 12 mg. Discontinuation, however, peaked at 9 mg rather than increasing steadily with dose.
Seven deaths were recorded among the 1,152 randomized participants during the 80-week study, including six assigned to retatrutide and one to placebo. Investigators assessed all seven deaths as unrelated to the study medication. The counts and investigator assessments appear in the published TRIUMPH-2 safety findings.
The count alone does not establish a drug-related mortality risk. Nor does the investigator assessment replace longer safety monitoring. A reliable expected-mortality comparison would need a matched population with similar age and health characteristics.
About 84% completed the assigned study drug. The publication reports 965 participants completing treatment, but its abstract does not provide a full explanation of every early discontinuation.
For someone losing substantial weight, persistent nausea or diarrhea may still make the medication difficult to continue. That is where the tolerability figures have direct consequences for treatment.
Research funding disclosure: Eli Lilly funded TRIUMPH-1 and TRIUMPH-2 and is developing retatrutide. Company efficacy estimates are identified separately from peer-reviewed findings. The author and publisher have not supplied a verified declaration of their own financial relationships.
Retatrutide Is Still Awaiting FDA Approval
Eli Lilly plans to submit a Biologics License Application in the first quarter of 2027, according to its second-quarter financial release filed with the SEC.
FDA reviewers must assess effectiveness, safety, manufacturing and proposed prescribing information. Retatrutide has no approved retail formulation or confirmed commercial price.
Why Is Reta Already Being Sold Online If It Is Not Approved?
Websites advertise Reta, retatrutide peptide and research retatrutide despite the drug’s investigational status.
The FDA warning on unapproved GLP-1 drugs states that retatrutide cannot legally be used in compounding.
Do not inject a vial sold online as Reta.
A mislabeled or contaminated injectable product can expose buyers to an incorrect dose or serious infection. Anyone who experiences a suspected reaction can report it through the FDA’s MedWatch safety reporting system.
The FDA issued a warning letter to Gram Peptides on March 31, 2026, concerning unapproved products advertised through its website.
Five additional letters dated August 24 addressed sellers marketing retatrutide or coded versions of the substance.
- NuScience Peptides LLC
- Peptide Partners LLC
- TXP Innovations LLC, operating as Tex Peptides
- Royal Peptides LLC
- Peak Performance Peptides
The six letters document FDA enforcement against multiple sellers of an unapproved experimental drug.
We previously covered the withdrawal of the Hims & Hers copycat Wegovy pill following regulatory scrutiny. Retatrutide presents an additional concern because no approved original medicine exists.
When Will Retatrutide Be Available by Prescription?
There is no confirmed U.S. prescription release date. Lilly intends to seek approval in early 2027, but availability depends on the FDA decision.
Eligible volunteers can receive investigational retatrutide through authorized trials. Study locations and eligibility criteria are listed in the ClinicalTrials.gov retatrutide records.
Clinical trials provide controlled medication supplies and medical supervision. Online sellers cannot provide equivalent assurance about an experimental injectable substance.
Pricing remains unknown. Approved obesity medicines such as Wegovy and Zepbound have carried substantial U.S. list prices, although discounts and insurance arrangements affect patient costs. No confirmed retatrutide retail price or coverage policy exists.
The Biggest Unanswered Question Is What Happens After Treatment Stops
Retatrutide has produced major weight-loss results. Yet no head-to-head trial has established that it outperforms Zepbound, and no equivalent randomized withdrawal study has determined how much weight patients regain after stopping treatment.
The potential patient population is large. The CDC National Health and Nutrition Examination Survey reported obesity prevalence of 40.3% among U.S. adults during August 2021 through August 2023, including 9.4% with severe obesity. We examined the figures further in our U.S. weight and obesity statistics.
Four in ten American adults.
Additional studies are investigating retatrutide for complications including obstructive sleep apnea and knee osteoarthritis. Their results will help establish clinical benefits outside weight reduction.
| Medication | Weight Regain After Stopping | Evidence |
|---|---|---|
| Semaglutide | About two-thirds of previous weight loss regained within one year | STEP-1 extension |
| Tirzepatide | 14% average regain over 52 weeks after switching to placebo | SURMOUNT-4 |
| Retatrutide | No equivalent randomized withdrawal result reported | TRIUMPH-1 extension measured continued dosing, not withdrawal |
Substantial regain followed withdrawal from semaglutide and tirzepatide in their respective studies. The absence of comparable retatrutide results is a major limitation for estimating its lasting value.
Retatrutide has demonstrated substantial weight loss, but its three-receptor design has not been shown to outperform tirzepatide at comparable tolerability. Direct comparative trials and withdrawal results will determine the stronger long-term treatment. The planned FDA application will advance regulatory review, but approval alone will not settle those questions.
Editorial information: NCHStats based this article on peer-reviewed studies, company trial results and FDA enforcement documents. Internal links refer to our previous reporting. Manufacturer links are included for identification and comparison.
