Retatrutide produced the largest weight loss yet reported in phase 3 obesity trials: 25.0% at the top dose in adults without diabetes and 18.8% in adults with type 2 diabetes, over 80 weeks. As of October 9, 2026, it is not FDA approved, Lilly plans to file in the first quarter of 2027, and there is no lawful source for your patients today.
Retatrutide adds a third receptor to the tirzepatide model
Retatrutide is a single peptide that activates three receptors: GIP, GLP-1 and glucagon. Tirzepatide hits the first two. Semaglutide hits GLP-1 alone. The TRIUMPH-2 authors call its safety profile “generally consistent with other molecules with GLP-1 receptor agonism.” For patients: same class of side effects, more weight loss, less long-term experience.
Trials gave it as a once-weekly injection. This post gives no dosing guidance.
The peer-reviewed results so far
Phase 2 obesity (NEJM, 2023). 338 adults with obesity, or overweight plus a weight-related condition, were treated for 48 weeks. Weight change at 48 weeks was -24.2% on 12 mg versus -2.1% on placebo. GI events were dose related and mostly mild to moderate. The authors also reported “dose-dependent increases in heart rate” that peaked at 24 weeks and declined afterward (PMID 37366315).
Phase 2 type 2 diabetes (Lancet, 2023). 281 adults with type 2 diabetes were randomized to retatrutide, placebo or dulaglutide 1.5 mg. At 24 weeks HbA1c fell 2.02 percentage points on 12 mg, versus 0.01 on placebo and 1.41 on dulaglutide. At 36 weeks weight fell 16.94% on 12 mg versus 3.00% on placebo. No severe hypoglycemia was reported (PMID 37385280).
TRIUMPH-1 (NEJM, published online September 29, 2026). 2,339 adults with obesity and without diabetes received 4, 9 or 12 mg or placebo for 80 weeks. Weight change was -17.6%, -23.7% and -25.0% versus -3.9% on placebo. In subgroups, retatrutide reduced knee osteoarthritis pain scores and apnea-hypopnea events compared with placebo. The most common adverse events were GI (PMID 42814954, doi:10.1056/NEJMoa2604169).
TRIUMPH-2 (Lancet, October 10, 2026 issue; presented at EASD 2026 in Milan). 1,152 adults with BMI 27 or higher and type 2 diabetes (HbA1c 6.5% to 10.5%) were randomized 1:1:1:1 to 4, 9 or 12 mg or placebo for 80 weeks (PMID 42810372, doi:10.1016/S0140-6736(26)01861-1).
- Primary endpoint: percent change in body weight at week 80 for 9 mg and 12 mg versus placebo.
- Result: -11.9% (4 mg), -16.8% (9 mg), -18.8% (12 mg) versus -5.1% (placebo). Placebo-adjusted difference at 12 mg: -13.8 percentage points.
- Discontinuation for adverse events or death: 4% (4 mg), 12% (9 mg), 8% (12 mg), 5% (placebo).
- Main adverse events: diarrhea 34% on 12 mg versus 13% on placebo; nausea 28% versus 8%.
- Hypotension: 6% on 12 mg versus under 1% on placebo. Dysesthesia: 7% on 12 mg versus 1% on placebo.
Lilly’s press releases headline TRIUMPH-2 at 20.8% versus 4.0%. That figure uses the “efficacy estimand,” which assumes everyone stayed on drug. The Lancet primary analysis counts people who stopped: 18.8% versus 5.1%. The lower number is the one to quote.
Company toplines fill in the rest of the program
Two more phase 3 trials have been reported only in Lilly press releases. Treat them as company-reported topline results, not peer reviewed.
- TRIUMPH-3 (July 23, 2026): adults with BMI 35 or higher and established cardiovascular disease, 80 weeks. Lilly reports -22.6% on 12 mg versus -3.2% on placebo (efficacy estimand). Discontinuation for adverse events was 13.5% on 12 mg versus 4.8% on placebo.
- TRIUMPH-4 (December 11, 2025): adults with obesity and knee osteoarthritis, without diabetes, 68 weeks. Lilly reports -28.7% on 12 mg versus -2.1% on placebo (efficacy estimand), or -23.7% versus -4.6% under the treatment-regimen estimand. Discontinuation for adverse events was 18.2% on 12 mg versus 4.0% on placebo.
| Trial | Population | Duration | Top-dose result (12 mg) | Placebo | Source |
|---|---|---|---|---|---|
| Phase 2 obesity | Obesity or overweight plus comorbidity | 48 weeks | -24.2% weight | -2.1% | NEJM 2023, PMID 37366315 |
| Phase 2 T2D | Type 2 diabetes | 36 weeks (weight) | -16.94% weight; HbA1c -2.02 pts at 24 weeks | -3.00%; -0.01 pts | Lancet 2023, PMID 37385280 |
| TRIUMPH-1 | Obesity, no diabetes | 80 weeks | -25.0% weight | -3.9% | NEJM 2026, PMID 42814954 |
| TRIUMPH-2 | Obesity or overweight with T2D | 80 weeks | -18.8% weight | -5.1% | Lancet 2026, PMID 42810372 |
| TRIUMPH-3 | BMI 35+ with cardiovascular disease | 80 weeks | -22.6% weight (efficacy estimand) | -3.2% | Lilly topline, July 23, 2026 |
| TRIUMPH-4 | Obesity with knee osteoarthritis | 68 weeks | -28.7% weight (efficacy estimand) | -2.1% | Lilly topline, Dec. 11, 2025 |
The safety signals are familiar, with two to watch
GI events dominate, as with every drug in this class, and they rise with dose. Two signals deserve a sentence when patients ask.
Dysesthesia. Abnormal skin sensation was reported more often on retatrutide in TRIUMPH-2 (7% versus 1% at 12 mg) and, per Lilly, in 20.9% of TRIUMPH-4 participants on 12 mg. Lilly describes these events as generally mild and mostly resolving on treatment. The mechanism is not established in the papers reviewed here.
Heart rate and blood pressure. Phase 2 showed dose-dependent heart rate increases that peaked and then declined. TRIUMPH-2 reported more hypotension on retatrutide. In TRIUMPH-3, Lilly’s own cardiovascular event counts were small and the confidence intervals crossed 1, so they do not establish benefit or harm.
Discontinuation for adverse events at the higher doses ran roughly two to four times placebo across the phase 3 trials.
The fair case for retatrutide, and what is still unknown
If approved, retatrutide would be a major advance in efficacy. Mean weight loss in the mid-twenties, in a large phase 3 trial, has until now been a surgical-range outcome. Patients who ask are reading accurate headlines.
What the published data do not yet answer: safety beyond 80 weeks, how much of the lost weight is lean mass (the abstracts reviewed here do not report body composition), whether the heart rate and dysesthesia signals matter over years, and hard cardiovascular outcomes. Pricing and coverage have not been announced.
What to tell patients
- It is not approved. Retatrutide is investigational. Lilly says it plans to submit a Biologics License Application to FDA in Q1 2027 (company statement, September 29, 2026).
- There is no lawful source today. FDA states that “retatrutide and cagrilintide cannot be used in compounding under federal law” and that these ingredients “have not been found safe and effective for any condition” (FDA). Outside a clinical trial, no pharmacy can lawfully dispense it. Our retatrutide status page tracks this.
- Gray-market vials are a real risk. Products sold as “research use only” are, in FDA’s words, “of unknown quality” and have been sold “directly to consumers for human use with dosing instructions.” The patient cannot know the identity, dose, sterility or endotoxin level of what is in the vial. See why the research-use label does not protect anyone and why retatrutide is not FDA approved.
- Approved options exist now. Tirzepatide (Zepbound, FDA approval announcement) and semaglutide (Wegovy prescribing information) are approved for chronic weight management. Status notes: tirzepatide, semaglutide.
- If they want retatrutide specifically, the lawful route is a clinical trial. ClinicalTrials.gov lists the open studies.
MDside’s position is plain: our providers do not prescribe retatrutide or any peptide without a lawful pathway.
What this means for you
Expect more questions after the September 29 publications. Quote the treatment-regimen numbers. Give every patient who asks the same three facts: not approved, no lawful source, approved alternatives available today. Document that conversation, especially if the patient mentions buying vials online. If you want a weight-management program built on approved drugs and a clear script for these visits, see our weight management oversight or book a call.
Frequently asked questions
Is retatrutide FDA approved?
No. As of October 9, 2026, retatrutide is investigational and not approved for any use. Eli Lilly has said it plans to submit a Biologics License Application to FDA in the first quarter of 2027. FDA states retatrutide cannot be used in compounding under federal law, so no pharmacy can lawfully supply it outside a clinical trial.
How much weight did people lose on retatrutide in phase 3?
In TRIUMPH-1, adults with obesity and without diabetes lost 25.0% of body weight on 12 mg over 80 weeks, versus 3.9% on placebo (NEJM 2026). In TRIUMPH-2, adults with type 2 diabetes lost 18.8% versus 5.1%. Lilly’s higher headline figures use an analysis that assumes everyone stayed on treatment.
What are the side effects of retatrutide?
The most common are gastrointestinal: nausea, diarrhea, vomiting, constipation and decreased appetite, rising with dose. Trials also reported dysesthesia, an abnormal skin sensation, more often than placebo, plus hypotension in TRIUMPH-2 and heart rate increases in phase 2. Discontinuation for adverse events at higher doses ran above placebo.
Can a compounding pharmacy make retatrutide?
No. FDA states that retatrutide cannot be used in compounding under federal law because it is not a component of an FDA-approved drug. Products sold online as research peptides are not lawful for human use and are of unknown identity, dose and sterility, according to FDA.
What can patients use instead of retatrutide?
Tirzepatide (Zepbound) and semaglutide (Wegovy) are FDA approved for chronic weight management in eligible adults and are available now through a prescriber. Patients who want retatrutide specifically can look for an enrolling clinical trial on ClinicalTrials.gov. Approved drugs come with a known label, a regulated supply chain and years of safety data.
This is general information, not legal advice. Rules vary by state and change. Confirm your own facts with counsel.