Retatrutide is a new medication (still in development and not FDA-approved for treatment at this stage) that holds promise for helping people manage obesity and other related health issues. As of September 2026, the retatrutide dosage picture is far clearer than it was a year ago. Five phase 3 trials have now reported, including the pivotal TRIUMPH-1 obesity trial, and every one of them used the same step-up dosing schedule.
This guide lays out that schedule in a simple chart, the weight loss seen at each dose, the side effects reported, and where retatrutide stands with the FDA. It also covers what clinicians should tell patients who are asking about it today. If you are weighing it against the approved dual agonist, our retatrutide vs tirzepatide comparison covers the differences side by side.
⚠ Safety Notice: Retatrutide is an investigational therapy currently in clinical development and is not FDA-approved for routine clinical use. Information on this page is provided for educational purposes for licensed healthcare professionals and should not be used as medical advice or as a basis for self-treatment. Retatrutide products marketed online, including those labeled for “research use” or referred to informally as “reta,” are not verified for safety, quality, or sterility and may pose serious risks. Retatrutide should be obtained only through authorized clinical research settings.
Retatrutide is a multi-functional peptide drug that acts as an agonist of the glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon receptors. This multifaceted approach enhances satiety, increases energy expenditure, and improves glucose metabolism. The drug is designed as a treatment for obesity, type 2 diabetes, and potentially other related metabolic disorders.
That third target is what sets it apart. Semaglutide (Wegovy®, Ozempic®) acts on GLP-1 alone, and tirzepatide (Zepbound®, Mounjaro®) acts on GLP-1 and GIP. Retatrutide adds the glucagon receptor, which is thought to raise energy expenditure. Early trials suggested it could be a game-changer, and the phase 3 results reported between December 2025 and July 2026 have largely borne that out. It is still an investigational compound (developed under the code name LY3437943), and it cannot be prescribed until the FDA approves it.
There is still no FDA-approved retatrutide dosage chart, because retatrutide is not yet approved. What does exist now is a consistent schedule used across the entire phase 3 program. Every participant started at 2 mg once a week and moved up one step every 4 weeks until reaching their assigned maintenance dose, then stayed there.
| Weeks | 4 mg group | 9 mg group | 12 mg group |
|---|---|---|---|
| 1–4 | 2 mg | 2 mg | 2 mg |
| 5–8 | 4 mg (maintenance) | 4 mg | 4 mg |
| 9–12 | 4 mg | 6 mg | 6 mg |
| 13–16 | 4 mg | 9 mg (maintenance) | 9 mg |
| 17 onward | 4 mg | 9 mg | 12 mg (maintenance) |
Once-weekly injection schedule used in the TRIUMPH and TRANSCEND phase 3 trials (Eli Lilly and Company, 2025–2026). This is a clinical trial protocol, not a prescribing schedule. There is no approved retatrutide dose because there is no approved product.
The earlier phase 2 study tested maintenance doses of 1, 4, 8, and 12 mg. The phase 3 program moved to 4, 9, and 12 mg, adding 6 mg as a stepping stone, so 9 mg (not 8 mg) is now the middle dose in the current evidence. Weekly doses such as 5 mg or 10 mg, which often come up in online searches, were not studied as maintenance doses in either program.
| Program | Maintenance doses studied | Starting dose | Step-up interval |
|---|---|---|---|
| Phase 2 (2023) | 1, 4, 8, 12 mg | 1, 2, or 4 mg | Every 4 weeks |
| Phase 3 (2025–2026) | 4, 9, 12 mg | 2 mg | Every 4 weeks (2 → 4 → 6 → 9 → 12 mg) |
Sources: Jastreboff et al., 2023; Eli Lilly and Company, 2026.
In the trials, retatrutide doses were measured in milligrams and supplied by the manufacturer under study conditions. Questions about “units,” “mL,” or how much liquid to mix into a vial come from unregulated “research” products. A units figure depends entirely on how an unverified vial was prepared, and the contents of those vials have not been checked for identity, strength, or sterility. Any conversion would give false confidence, which is why this guide does not provide one, and why no clinician should rely on one.
The dosing evidence now comes from two stages of research: a 2023 phase 2 study that first compared dose levels, and a phase 3 program that tested the chosen doses in several thousand participants across obesity, type 2 diabetes, knee osteoarthritis, and heart disease.
TRIUMPH-1 enrolled 2,339 adults with obesity, or overweight plus at least one weight-related health condition, who did not have diabetes. Participants were randomly assigned to 4 mg, 9 mg, 12 mg, or placebo for 80 weeks. Here is the average weight loss among people who stayed on treatment:
Average weight loss at 80 weeks (TRIUMPH-1)
Efficacy estimand. Average baseline BMI 40.0. Source: Eli Lilly and Company, May 21, 2026.
The higher doses also moved many people into weight-loss ranges long associated with bariatric surgery:
| Dose | Lost 25% or more | Lost 30% or more | Lost 35% or more |
|---|---|---|---|
| 4 mg | 27.8% | 15.3% | 5.9% |
| 9 mg | 52.9% | 37.9% | 20.8% |
| 12 mg | 62.5% | 45.3% | 27.2% |
| Placebo | 2.2% | 0.5% | 0.3% |
Share of participants reaching each weight-loss threshold at 80 weeks.
Among the 532 participants who continued to 104 weeks, those who started on 12 mg averaged about 30% weight loss. And 37.5% of people who began the trial with class 3 obesity (BMI of 40 or higher) had a BMI below 30 by week 80. Waist circumference, blood pressure, triglycerides, non-HDL cholesterol, and a marker of inflammation (hs-CRP) all improved as well.
| Trial (reported) | Who was studied | Length | Key results |
|---|---|---|---|
| TRIUMPH-4 (Dec 2025) | Obesity or overweight plus knee osteoarthritis | 68 weeks | 26.4% weight loss on 9 mg and 28.7% on 12 mg (placebo 2.1%). Knee pain scores fell about 75%, vs about 40% on placebo. |
| TRANSCEND-T2D-1 (Mar 2026) | Type 2 diabetes managed with diet and exercise | 40 weeks | A1C fell 1.7 to 2.0 points from 7.9%. Weight fell 11.5% to 16.8%. |
| TRIUMPH-1 (May 2026) | Obesity or overweight, no diabetes | 80 weeks | 19.0%, 25.9%, and 28.3% weight loss on 4, 9, and 12 mg (placebo 2.2%). |
| TRIUMPH-2 (Jul 2026) | Type 2 diabetes plus obesity or overweight | 80 weeks | 12.7%, 19.1%, and 20.8% weight loss on 4, 9, and 12 mg (placebo 4.0%). A1C fell 1.4 to 1.6 points. |
| TRIUMPH-3 (Jul 2026) | BMI 35 or higher plus established heart disease | 80 weeks | 21.6% weight loss on 9 mg and 22.6% on 12 mg (placebo 3.2%). No statistically significant reduction in major heart events yet. |
Efficacy estimand results from Eli Lilly and Company announcements, December 2025 to July 2026.
One pattern matters for dosing conversations. People with type 2 diabetes lost noticeably less weight at the same doses: about 21% on 12 mg in TRIUMPH-2, compared with about 28% in TRIUMPH-1. The same gap is seen with semaglutide and tirzepatide, so it is a familiar counseling point for anyone already prescribing GLP-1 medications.
Researchers did a study that lasted nearly a year with 338 adults who were not diabetic but were overweight or obese, published in the New England Journal of Medicine (Jastreboff et al., 2023). These participants were split into six groups and each group received a different amount of the medicine:
The study showed that the more medicine participants took, the more weight they lost. For example, those on the lowest dose lost about 8.7% of their weight, while those on the highest dose lost 24.2%.
Every participant taking the highest doses of the medication lost at least 5% of their starting weight. They also had improvements in waist size, blood pressure, blood sugar levels, and other health markers, although there wasn’t an increase in “good” cholesterol.
The bigger follow-up study mentioned in earlier versions of this guide was TRIUMPH-1. It has now finished, and its results are shown above.
As with other incretin medications, side effects in the trials were mostly gastrointestinal, were more common at higher doses, and tended to cluster during dose escalation. The table shows how often each was reported in TRIUMPH-1:
| Side effect | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhea | 25.2% | 34.1% | 32.0% | 13.5% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Dysesthesia | 5.1% | 12.3% | 12.5% | 0.9% |
| Stopped due to side effects | 4.1% | 6.9% | 11.3% | 4.9% |
Source: Eli Lilly and Company, TRIUMPH-1 results, May 21, 2026.
Dysesthesia means an unusual or unpleasant skin sensation, such as tingling, burning, or sensitivity to touch. It was not a prominent finding with semaglutide or tirzepatide, which makes it one of the more distinctive signals in the retatrutide program. Lilly reports that these events were generally mild to moderate and that most resolved during treatment.
Tolerability also appears to depend on body size. In TRIUMPH-4, 18.2% of all participants on 12 mg stopped treatment because of side effects, but only 12.1% of those with a BMI of 35 or higher did. The phase 2 study also reported a dose-related rise in heart rate. If retatrutide is approved, dose selection, slow escalation, and monitoring will matter as much as they do with today’s GLP-1 medications.
We follow these developments each month; our June 2026 GLP-1 clinical practice update covers what the phase 3 multi-agonist data mean for practice.
Patients are hearing about retatrutide long before they can get it. A clear, consistent message protects them and your practice:
The skills that will matter if retatrutide is approved (patient selection, gradual titration, side-effect management, and monitoring) are the same ones clinicians use with GLP-1 medications right now. You can sample IAPAM’s clinical GLP-1 training with the free 1-CME module below.
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No. As of September 2026, retatrutide is an investigational medication and is not approved by the FDA for any use. Five phase 3 trials have reported results, and Eli Lilly has said it plans to submit its application to the FDA in the first quarter of 2027.
There is no approval date yet. Lilly plans to file with the FDA in the first quarter of 2027, and approval could only follow once the FDA completes its review. Until then, retatrutide is available only through clinical trials and a narrow early access program run by Lilly.
Retatrutide is not approved, so there is no recommended dose for anyone to take on their own, and it should not be self-administered. In the phase 3 clinical trials, participants started at 2 mg once weekly under medical supervision and increased every 4 weeks toward an assigned maintenance dose of 4 mg, 9 mg, or 12 mg. The highest dose studied was 12 mg once weekly.
In the 80-week TRIUMPH-1 trial in adults without diabetes, average weight loss was 19.0% on 4 mg, 25.9% on 9 mg, and 28.3% on 12 mg, compared with 2.2% on placebo. People with type 2 diabetes lost less at the same doses, about 21% on 12 mg in the TRIUMPH-2 trial.
The most common side effects in trials were nausea, diarrhea, constipation, and vomiting, and they increased with dose. Dysesthesia, an unusual skin sensation such as tingling, burning, or sensitivity to touch, was also reported more often than with placebo. In TRIUMPH-1, 11.3% of people on the 12 mg dose stopped treatment because of side effects, compared with 4.9% on placebo.
Only through a clinical trial or Lilly’s early access program, which is limited to adults with severe obesity and serious complications who cannot join a trial. Products sold online as research-use retatrutide are unapproved new drugs, and the FDA has issued warning letters to sellers, rejecting the research use only label as a defense.
Clinical trials measured retatrutide doses in milligrams using doses supplied by the manufacturer. A units or mL figure depends entirely on how an unregulated vial was prepared, and the contents of those vials are not verified for identity, strength, or sterility. Any such conversion would give false confidence, so this guide does not provide one.
The phase 3 results suggest that retatrutide may represent a pivotal advance in the management of obesity and related disorders. With its unique multi-receptor targeting mechanism, it produced average weight loss approaching 30% at the highest dose, and the trials settled on a clear step-up schedule from 2 mg to a maintenance dose of 4, 9, or 12 mg. However, like all emerging therapies, the pathway to routine clinical use still requires FDA review of its safety, optimal dosing, and long-term effects.
Until that review is complete, retatrutide remains investigational, and there is no approved dose for patients. The best preparation for clinicians is mastery of the GLP-1 medications available today. IAPAM’s GLP-1 certification training for medical weight management providers covers semaglutide and tirzepatide protocols, patient selection, and long-term management, with up to 6 AMA PRA Category 1 CME credits online. Many providers pair it with IAPAM’s Botox® training to build a broader practice.
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Safety Advisory: Retatrutide remains an investigational agent under study and is not approved by the FDA or other major regulatory authorities for general clinical use. Products sold online as retatrutide or “research-only” retatrutide are not regulated or verified, and their contents, labeling, and sterility cannot be assured. Use outside authorized clinical trials is not supported, and patients should be directed to consult a licensed clinician for individualized care.
Disclaimer: The information provided here is for general knowledge only and should not be considered medical advice. For any questions or concerns about your health or medications, please consult your physician or healthcare provider. They are best equipped to provide guidance specific to your medical needs.
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Safety Advisory: Retatrutide remains an investigational agent under study and is not approved by the FDA or other major regulatory authorities for general clinical use. Products sold online as retatrutide or “research-only” retatrutide are not regulated or verified, and their contents, labeling, and sterility cannot be assured. Use outside authorized clinical trials is not supported, and patients should be directed to consult a licensed clinician for individualized care.
Disclaimer: The information provided here is for general knowledge only and should not be considered medical advice. For any questions or concerns about your health or medications, please consult your physician or healthcare provider. They are best equipped to provide guidance specific to your medical needs.
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