Retatrutide Phase 3 TRIUMPH-4: 28.7% Weight Loss in 68 Weeks
Eli Lilly released the full Phase 3 TRIUMPH-4 dataset for retatrutide in December 2025, and the numbers are the largest ever reported in a late-stage obesity trial. At the 12mg dose, patients lost an average of 28.7% of their starting body weight over 68 weeks. The 9mg dose came in at 26.4%. For context, the two GLP-1 drugs currently dominating the weight-loss market, semaglutide and tirzepatide, have never crossed 25% in their own pivotal readouts. If retatrutide makes it through FDA review intact, it becomes the new efficacy ceiling.
Retatrutide (development code LY3437943) is a triple agonist, meaning a single molecule activates three different receptors at once: GIP, GLP-1, and glucagon. Tirzepatide is a dual agonist (GIP plus GLP-1), semaglutide is a mono-agonist (GLP-1 only). Adding glucagon receptor activity is the lever Lilly is pulling. In theory, it pushes the body toward higher energy expenditure on top of the appetite suppression the other two mechanisms deliver. TRIUMPH-4 is the readout that had to validate whether that theoretical edge shows up in actual patients over a full year.
The efficacy picture
The 68-week trial randomized adults with obesity to one of three retatrutide doses or placebo. At the top dose, the average participant lost about 28.7% of body weight. For someone starting at 220 pounds, that is roughly 63 pounds. The 9mg group averaged 26.4%, and even the lower doses beat placebo by wide margins. Weight loss was still trending down at the 68-week mark rather than plateauing, which suggests a longer trial might have shown even larger totals. Lilly has not committed to running one.
One unexpected secondary finding jumped out. Patients with osteoarthritis pain reported meaningful improvement on retatrutide versus placebo. This is the first obesity drug to register an OA pain benefit as a pre-specified outcome. Whether the effect is driven by the weight loss itself, the glucagon receptor activity, or something else is not clear yet, but it opens a door that neither Wegovy nor Zepbound has walked through.
A new safety signal: dysesthesia
The trial also surfaced something new. Roughly 20.9% of patients on the 12mg dose reported dysesthesia, compared to 0.7% on placebo. Dysesthesia is the clinical term for an abnormal skin sensation that appears without an obvious physical cause. Patients describe it as burning, tingling, prickling, or a pins-and-needles feeling that will not go away. It is uncomfortable, and in some cases it is enough to make people stop treatment.
A 20-fold excess over placebo is the kind of signal the FDA reads carefully. Most cases in TRIUMPH-4 were classified as mild or moderate and did not require hospitalization, but the finding will show up in the label and it will almost certainly shape how clinicians talk about risk with patients. It also helps explain the other number worth paying attention to: 18.2% of patients on the 12mg dose discontinued treatment before the study ended, which is notably higher than the discontinuation rates reported for semaglutide and tirzepatide in their pivotal trials.
Timeline to approval
Lilly has indicated that the New Drug Application for retatrutide will be submitted in late 2026 or the first quarter of 2027. Under a standard 10-month FDA review, that puts a possible approval decision somewhere in mid-2027. Actual commercial availability usually trails approval by a few months while manufacturing, labeling, and distribution come online, so patients realistically should not expect retatrutide at a pharmacy counter before the second half of 2027 at the earliest.
What to do in the meantime
Retatrutide is not for sale. Any product marketed under the retatrutide name right now is either research-grade material sold under a not-for-human-use disclaimer or a compounded preparation operating outside the legal framework. Neither is a safe path. If you need a GLP-1 therapy today, the approved options are tirzepatide (Mounjaro, Zepbound) and semaglutide (Ozempic, Wegovy), both of which have years of real-world data behind them.
If you are trying to decide between them, our retatrutide vs semaglutide and retatrutide vs tirzepatide pages line up efficacy, side effects, cost, and FDA status side-by-side. You can also run the numbers on what a year of treatment would cost you with the cost calculator.
What to watch next
Three things will shape the retatrutide story over the next 18 months. First, whether Lilly files the NDA on schedule. Second, whether the dysesthesia signal tightens or softens once a broader patient population is pooled and pharmacovigilance data lands. Third, how the FDA weighs the 28.7% efficacy number against the 18.2% discontinuation rate in the final label. A boxed warning, a narrower indication, or a step-therapy requirement would change the commercial picture even if the drug clears review. We will update this page as each of those data points lands.
Frequently Asked Questions
No. As of early 2026 retatrutide is still an investigational drug. Eli Lilly is expected to submit the New Drug Application in late 2026 or Q1 2027, with a potential FDA decision around mid-2027. It cannot be legally prescribed or sold for weight management in the United States today.
In the TRIUMPH-4 Phase 3 readout, retatrutide 12mg produced 28.7% average body weight loss over 68 weeks. By comparison, semaglutide (Wegovy) has delivered roughly 15% in its pivotal trials and tirzepatide (Zepbound) has delivered roughly 22.5% at the 15mg dose. Retatrutide also showed a signal for improvement in osteoarthritis pain, which neither Wegovy nor Zepbound has demonstrated as a secondary outcome. The tradeoff is a newer safety profile and a higher discontinuation rate.
Assuming the NDA is submitted in late 2026 or early 2027 and the FDA grants a standard 10-month review, commercial launch is most likely mid-to-late 2027. Supply ramp-up has historically been slow for new GLP-1 class drugs, so real-world access may lag the approval date by several months.
Dysesthesia is an abnormal skin sensation such as burning, tingling, or a pins-and-needles feeling that occurs without a clear physical cause. In TRIUMPH-4 it was reported in 20.9% of patients on the 12mg retatrutide dose versus 0.7% on placebo, which is a meaningful signal. Most cases in the trial were described as mild to moderate, but it is a finding that clinicians and the FDA will look at closely during the review, and it is one of the reasons some patients discontinued treatment.
Not legally in the United States. Retatrutide is not approved, not available through licensed compounding, and not sold by any legitimate pharmacy for weight management. Patients seeking treatment today should work with a clinician on approved alternatives like Wegovy (semaglutide) or Zepbound (tirzepatide). Research-grade material sold online is not pharmaceutical grade and is not intended for human use.
Medical Disclaimer
The information provided on this page is for educational and informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting, stopping, or modifying any peptide therapy or medication. PeptideVS does not endorse, recommend, or promote the use of any specific peptide for medical treatment. Clinical data cited may be from ongoing trials and is subject to change. Individual results may vary.