Reta is the nickname for retatrutide, an experimental weight loss drug developed by Eli Lilly. In the Phase 3 TRIUMPH-1 trial, people receiving the highest tested dose lost an average of 28.3% of their starting body weight over 80 weeks, equivalent to 70.3 pounds.
The trial involved adults with obesity who did not have diabetes. Its results place retatrutide among the most promising experimental weight loss medicines, although the drug has not been tested directly against every established alternative.
Unlike Ozempic and Wegovy, retatrutide activates three hormone receptors involved in appetite and metabolism. That additional pathway may help explain the weight loss observed in trials, but its contribution to individual benefits and side effects is still being studied.
Retatrutide is not FDA-approved. Eli Lilly is still developing the treatment, and the FDA has warned companies against marketing unapproved retatrutide products. Vials advertised online as Reta are not equivalent to the investigational medication administered under medical supervision in clinical trials.
A 28.3% average reduction is a major result. The harder question is how long patients can maintain it, particularly if they stop treatment because of side effects or cost.
How Effective Is Reta for Weight Loss?
Video: An explanation of retatrutide and its potential role in weight management. The clip is supplementary commentary, not the source of the clinical trial figures.
Retatrutide is designed as a once-weekly injection. It activates receptors for three hormones that regulate appetite, 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. Semaglutide targets GLP-1 receptors, and tirzepatide activates GLP-1 and GIP receptors. Retatrutide adds glucagon receptor activity, which researchers are studying for its contribution to energy expenditure and weight reduction.
The combination is scientifically interesting because glucagon also stimulates glucose production. The researchers aim to achieve substantial weight reduction without losing the benefits of the other hormonal pathways.
The trial findings demonstrate considerable weight loss, but the clinical value depends on more than the average percentage. In TRIUMPH-2, roughly one in six participants did not complete the assigned study drug. Gastrointestinal reactions were among the reported reasons for discontinuation.
A treatment intended for years of obesity management must remain tolerable over time. The efficacy figures are impressive, but they do not remove that concern.
How Much Weight Can You Lose on Retatrutide?
The highest dose produced 28.3% average weight loss after 80 weeks, equivalent to 70.3 pounds in the TRIUMPH-1 study population. Nearly half of participants receiving 12 mg lost at least 30% of their starting weight.
TRIUMPH-1 was a randomized, double-blind Phase 3 study comparing weekly injections of 4 mg, 9 mg and 12 mg against placebo. Weight reduction increased across the tested doses.
| TRIUMPH-1 Finding | Reported Result |
|---|---|
| Study duration | 80 weeks |
| Study population | Adults with obesity, without diabetes |
| Highest dose studied | 12 mg weekly |
| Average weight loss at 12 mg | 28.3% |
| Average weight loss in pounds | 70.3 pounds |
| Participants at 12 mg losing at least 30% | 45.3% |
Source: Eli Lilly TRIUMPH-1 results, May 21, 2026, efficacy table, primary endpoint and weight-loss responder analysis.
The responder figures are especially revealing. At 12 mg, 45.3% lost at least 30% of their starting weight, compared with just 0.5% receiving placebo. The average therefore represents substantial reductions across a large share of the treatment group, not just a handful of unusually strong responses.
Selected participants continued into a 24-week extension. Among those with a starting BMI of at least 35, average weight loss reached 30.3% at 104 weeks in the highest-dose group.
The Eli Lilly TRIUMPH-1 extension update also reported an average loss of 85 pounds for that subgroup.
There is a limitation. Extension participants had completed the initial treatment period and tolerated their assigned medication, so the 104-week results do not represent everyone originally enrolled.
Evidence from approved medicines explains why long-term maintenance deserves attention. In the STEP-1 semaglutide withdrawal study, 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 increase among participants switched to placebo over 52 weeks, measured from randomization.
Equivalent randomized withdrawal data for retatrutide are not yet available. Its 80-week and 104-week results establish what happened during continued treatment, not what patients retain after stopping.
Retatrutide Also Produced Major Weight Loss in People With Type 2 Diabetes
Retatrutide has also delivered substantial results among patients with type 2 diabetes, a group that generally records smaller weight reductions in obesity medication trials.
TRIUMPH-2 enrolled 1,152 adults with overweight or obesity and type 2 diabetes. Participants received retatrutide or placebo over 80 weeks, with researchers monitoring body weight and blood sugar.
The TRIUMPH-2 study published in The Lancet reported the following treatment-regimen estimates.
| Weekly Treatment | Average Weight Loss at 80 Weeks |
|---|---|
| Retatrutide 4 mg | 11.9% |
| Retatrutide 9 mg | 16.8% |
| Retatrutide 12 mg | 18.8% |
| Placebo | 5.1% |
Source: TRIUMPH-2 published abstract, PubMed PMID 42810372, body-weight endpoint and treatment-regimen analysis.
At 12 mg, the treatment difference from placebo was 13.8 percentage points, with a reported 95% confidence interval of 11.8 to 15.8 percentage points.
The responder results were equally notable. According to the published TRIUMPH-2 analysis, 47% of participants receiving 12 mg lost at least 20% of their starting weight, and 31% lost at least 25%. The corresponding placebo figures were 6% and 3%.
Blood sugar improved alongside weight. Average HbA1c fell by 1.45 percentage points at the highest dose, compared with 0.45 percentage points on placebo. HbA1c measures average blood glucose over the preceding two to three months.
Another reported endpoint found that 72% of participants receiving 12 mg reached an HbA1c of 6.5% or lower, compared with 29% receiving placebo.
For patients managing obesity and type 2 diabetes together, those combined results are clinically significant. The FDA will determine the authorized indications after reviewing the completed development program.
Why the Exact Efficacy Numbers Depend on the Analysis
Video: Commentary discussing retatrutide trial results and their potential implications for weight loss treatment.
TRIUMPH-2 generated two reported weight-loss figures for its highest dose. Eli Lilly initially announced 20.8%, whereas the later peer-reviewed publication reported 18.8%.
Both came from the same trial. They used separate statistical approaches.
The earlier efficacy analysis estimated results under specified assumptions about treatment adherence and continuation. The treatment-regimen analysis accounted for participants regardless of discontinuation or other interventions, following the study methodology.
The July 23 Eli Lilly announcement contains the 20.8% estimate. It also included findings from TRIUMPH-3, a separate trial involving patients with severe obesity and established cardiovascular disease.
Expect to encounter 20.8% in coverage based on the initial announcement and 18.8% in reporting based on the treatment-regimen analysis. The figures describe separate estimates, not competing measurements of individual patients.
The statistical method determines how treatment discontinuation and adherence affect the reported average. That information belongs beside the percentage whenever a result is compared with another medication.
Differences Between Ozempic, Zepbound and Reta
Ozempic and Wegovy contain semaglutide, which activates GLP-1 receptors. Mounjaro and Zepbound contain tirzepatide, which activates GLP-1 and GIP receptors. Retatrutide adds glucagon receptor activity.
Counting receptors alone cannot tell patients which treatment will work best. Weight loss, tolerability and the ability to continue treatment are more useful measures.
| Medication | Active Ingredient | Hormone 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, or Reta | Retatrutide | GLP-1, GIP and glucagon | Investigational, not FDA-approved |
Ozempic and Mounjaro have approved indications for type 2 diabetes. Wegovy and Zepbound have approvals for chronic weight management and certain additional uses. Retatrutide currently has no FDA-approved indication.
Use of existing GLP-1 medications has expanded across the United States. NCHStats previously examined that trend in its report on GLP-1 medication use among American women.
TRIUMPH-1 and TRIUMPH-2 compared retatrutide with placebo, not directly with semaglutide or tirzepatide. A randomized head-to-head trial would provide a stronger assessment of relative effectiveness and adverse effects.
Comparing results across separate trials is less reliable because patient populations, treatment periods and statistical methods vary. The 28.3% figure alone is not proof that Reta outperforms Zepbound in the same patient population.
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 affected 14% to 28% of participants in the retatrutide groups, compared with 8% receiving placebo.
Video: Commentary on retatrutide safety, including gastrointestinal symptoms and other adverse effects reported during clinical testing.
At the upper end of the diarrhea range, 34% is roughly 2.6 times the placebo rate. The trial also recorded low blood pressure-related events and dysesthesia, which describes abnormal skin sensations such as burning or tingling.
| Reported Adverse Event | Retatrutide Groups | Placebo Group |
|---|---|---|
| Diarrhea | 27% to 34% | 13% |
| Nausea | 14% to 28% | 8% |
| Low blood pressure-related events | 1% to 6% | Less than 1% |
| Dysesthesia | 4% to 7% | 1% |
| Permanent discontinuation due to adverse events or death | 4% to 12% | 5% |
Source: TRIUMPH-2, The Lancet, published safety and adverse-event analysis. Ranges represent the reported treatment groups.
Permanent discontinuation due to adverse events or death occurred in 4% of participants assigned to 4 mg, 12% assigned to 9 mg and 8% assigned to 12 mg. The placebo rate was 5%, according to the TRIUMPH-2 safety results.
Seven deaths were recorded across the trial groups, including six participants assigned to retatrutide and one assigned to placebo. Investigators assessed all seven deaths as unrelated to the study medication.
About 84% of participants completed the study drug. Discontinuations occurred for several reasons, rather than adverse effects alone.
For someone with severe obesity, losing more than a quarter of starting body weight could bring substantial medical benefits. Persistent nausea, diarrhea or other reactions may still prevent individual patients from continuing treatment.
That limits how confidently the trial average can predict everyday treatment outcomes. The 80-week findings also leave questions about rare serious adverse events, pancreatitis and cardiovascular outcomes during longer exposure.
Retatrutide Is Still Awaiting FDA Approval
Retatrutide remains an investigational drug. 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.
Submission is not approval. FDA reviewers must assess the evidence on effectiveness, safety, manufacturing and prescribing information before deciding if the drug should become available through the U.S. prescription market.
No approved retail formulation or commercial price has been announced.
Why Is Reta Already Being Sold Online If It Is Not Approved?
Websites already advertise products as Reta, retatrutide peptide and research retatrutide. Some use coded descriptions of the experimental compound.
The FDA warning on unapproved GLP-1 drugs states that retatrutide cannot legally be used in compounding. No retatrutide product has been approved as safe and effective for any indication.
Do not inject a vial sold online as Reta. An unapproved product may contain the wrong concentration, unidentified ingredients or microbial contamination. Those risks were not evaluated in the controlled clinical trials described above.
FDA enforcement records identify businesses marketing unapproved retatrutide products. On March 31, 2026, the agency issued a warning letter to Gram Peptides concerning products advertised through its website.
Five additional warning letters dated August 24, 2026, addressed businesses 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
Six dated letters are documented here, one from March and five from August. The enforcement actions concern multiple businesses selling or promoting an experimental substance that has never received FDA approval.
The earlier withdrawal of the Hims & Hers copycat Wegovy pill demonstrated how regulatory intervention can affect unapproved weight loss products. Retatrutide sellers face an additional issue because there is no approved original retatrutide medicine.
When Will Retatrutide Be Available by Prescription?
There is no confirmed U.S. prescription release date for retatrutide. Eli Lilly plans to seek FDA approval in early 2027, but commercial availability depends on the regulatory decision.
Eligible participants can currently receive investigational retatrutide through authorized clinical trials. Study locations, eligibility requirements and recruitment information appear in the official ClinicalTrials.gov retatrutide records.
Clinical trials provide controlled drug supplies and medical monitoring. Buying an experimental peptide from an online seller does not offer equivalent safeguards.
Pricing remains unknown. Existing obesity medicines such as Wegovy and Zepbound have carried substantial U.S. list prices, although insurance coverage and manufacturer programs affect what patients pay.
Retatrutide has no announced commercial price or coverage policy. Predictions about monthly costs or pharmacy availability are premature.
The Biggest Unanswered Question Is What Happens After Treatment Stops
Retatrutide has demonstrated substantial weight reduction in late-stage trials. TRIUMPH-1 reported an average loss of 28.3% at the highest dose, and TRIUMPH-2 recorded weight loss alongside improved blood sugar in adults with type 2 diabetes.
The potential patient population is large. Federal data discussed in our U.S. weight and obesity statistics show that 40.3% of American adults had obesity during the August 2021 to August 2023 measurement period, including 9.4% with severe obesity.
Additional studies are investigating retatrutide in obesity-related conditions such as obstructive sleep apnea and knee osteoarthritis. Results from those trials could clarify benefits outside weight reduction itself.
Yet the withdrawal evidence remains the largest gap. The 80-week results describe treatment response, not what happens after injections stop. Semaglutide and tirzepatide withdrawal studies have already shown substantial weight regain following discontinuation.
Long-term maintenance will also influence insurance decisions. Patients and insurers need evidence about sustained health benefits, particularly if treatment must continue for years to preserve the results.
Both TRIUMPH-1 and TRIUMPH-2 were funded by Eli Lilly, and the published papers disclose financial relationships involving company employees and shareholders. Regulatory review and further independent analysis will help establish long-term safety and clinical value.
Retatrutide has demonstrated major weight loss, but the durability of those reductions after treatment ends remains unknown. That question, together with tolerability and long-term safety, will determine its place in obesity treatment.
Editorial information: The article is based on peer-reviewed clinical research, manufacturer announcements and FDA enforcement records. Product websites are linked for identification and comparison.
