by At the top 12 mg dose, retatrutide has been reported to average about 24% to 28% weight loss in obesity trials, and up to 36.6 pounds in a diabetes trial. Those averages come from studies that ran 40 to 80 weeks, so they say nothing about a single month.
What weight-loss percentage did the Phase 2 trial show?
The earliest detailed numbers come from a 2023 Phase 2 study that a clinic summary says was published in the New England Journal of Medicine. It enrolled 338 adults with obesity or overweight, excluded people with type 2 diabetes, and ran 48 weeks. Average weight loss at 48 weeks, as that summary reports it:
| Group | Average weight loss at 48 weeks |
|---|---|
| Placebo | 2.1% |
| 1 mg | 8.7% |
| 4 mg (combined groups) | 17.1% |
| 8 mg (combined groups) | 22.8% |
| 12 mg | 24.2% |
The same summary says 83% of people on the 12 mg dose lost at least 15% of body weight, compared with 2% on placebo. It also notes that Eli Lilly, the company developing retatrutide, funded the trial.
What did the Phase 3 trials show?
A bariatric clinic's page describes a Phase 3 obesity trial, TRIUMPH-1, in which the 12 mg dose averaged 28.3% weight loss over 80 weeks, roughly 70 pounds. The page says 45% of participants crossed 30%. Those are the clinic's figures, so check them against the trial record before you rely on them.
A 2025 systematic review of retatrutide trials in PubMed, the U.S. National Library of Medicine's database, pooled three articles. It screened 1,082 patients, and 691 were randomly assigned: 510 to retatrutide and 130 to placebo. The review found the 12 mg dose produced the largest reductions in body weight, body mass index and waist circumference, and that weekly injections led to significant weight loss compared with placebo.
What did the diabetes trial show for weight and A1C?
Eli Lilly reported a Phase 3 trial in people with type 2 diabetes, as covered in a Yahoo Health report on the trial. Over 40 weeks, the 12 mg dose averaged up to 36.6 pounds of weight loss, and A1C, a measure of average blood sugar, fell 1.7 to 2 percent. The same report says the full results had not yet been published or peer-reviewed.
A clinic page also describes a March 2026 type 2 diabetes trial it calls TRANSCEND-T2D-1, with about 16.8% weight loss over 40 weeks and a meaningful A1C reduction. That may be the same study as the Eli Lilly report, so check the trial record before you compare them.
All the reported numbers side by side
| Trial as reported | Who was studied | Length | Reported result (dose) | A1C |
|---|---|---|---|---|
| 2023 Phase 2 (clinic summary) | Adults with obesity or overweight; type 2 diabetes excluded | 48 weeks | 24.2% average (12 mg) | — |
| TRIUMPH-1 Phase 3 (clinic page) | Adults with obesity | 80 weeks | 28.3%, about 70 pounds (12 mg) | — |
| Phase 3 diabetes trial (Eli Lilly, via Yahoo Health) | Adults with type 2 diabetes | 40 weeks | Up to 36.6 pounds average (12 mg) | Down 1.7 to 2 percent |
| March 2026 trial, TRANSCEND-T2D-1 (clinic page) | Adults with type 2 diabetes | 40 weeks | About 16.8% (the clinic page gives no dose) | Meaningful reduction, no figure given |
These figures come from different trials, populations and lengths, so they are not directly comparable.
Why do the percentages differ from one report to another?
Each trial enrolled different people, tested different doses and ran for a different length of time. Averages can also hide how many people reached a given level of loss. Each trial compares the drug with a placebo group, and how placebo response skews results (our research library) affects how large the gap looks.
When you read a retatrutide number, check:
- Which trial, dose and number of weeks it refers to.
- Whether it is an average or the share of people who reached a threshold.
- Whether it comes from a published paper, a company statement or a clinic summary.
- Whether the population includes people with type 2 diabetes.
How much weight can you lose in one month on retatrutide?
The trials above ran 40, 48 and 80 weeks, so a 30-pound drop in one month is not what they describe. A clinic page estimates 1 to 3% of body weight lost in the first four weeks, but that is an estimate, not a trial result. For context, Harvard Health's guide to how GLP-1s work says that in some studies, GLP-1 users lost an average of 10% to 15% of body weight over a year.
How does retatrutide's reported result compare with Zepbound?
Harvard Health says tirzepatide, sold as Zepbound, is FDA-approved for weight loss, and that the most effective GLP-1 medications can lead to weight loss of over 20% of body weight. A clinic page puts Zepbound at around 20% to 22%. Because those figures come from different trials, they cannot be ranked head to head.
What side effects and unknowns have been reported?
In the diabetes trial report, nausea, diarrhea and vomiting were the most common side effects. The 2025 systematic review also found gastrointestinal effects were the most commonly reported, and Harvard Health lists nausea, vomiting, diarrhea and constipation for the GLP-1 class. In the same diabetes trial, 2.3% to 4.5% of participants reported dysesthesia, a painful or burning sensation, which an endocrinologist quoted in the report says researchers will need to study further.
Harvard Health notes that rapid weight loss from GLP-1 drugs may lead to a decrease in muscle mass, and that a doctor may advise more protein to reduce that risk. Whether retatrutide affects muscle is a question for your provider. For how side effects compare across weight-loss drugs, see our safest weight-loss drug guide.
As of October 2026, retatrutide is investigational, and two clinic pages say it is not FDA-approved. A clinic page lists long-term safety beyond 48 weeks, cardiovascular outcomes, and results in more diverse groups, including people with diabetes, as open questions.
What should you check next?
- Ask which trial, dose and week count a number comes from.
- Look for the published paper or the trial record on ClinicalTrials.gov, which a clinic page points to for retatrutide trials.
- Ask a clinician whether a current research study fits your situation.
- Be wary of online sellers offering retatrutide. The National Academy of Medicine's GLP-1 basics page reports that the FDA recommends filling prescriptions at a state-licensed pharmacy.
- Track your weight, meals and movement alongside any treatment, as covered in our guide to the most effective way to lose weight.
By the New Life Wellness Guide Editorial Team
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.