Retatrutide vs Tirzepatide: What the Trials Report
Retatrutide is investigational and not available. What the published TRIUMPH and SURMOUNT trials reported for weight change and side effects, with sources.
By Juan Montes
Updated October 19, 2026 · 6 min read
PrescribedRX is a telehealth platform; prescriptions are written by licensed clinicians and filled by licensed partner pharmacies.
Short answer: Retatrutide is an investigational drug that is not available, unlike prescription tirzepatide, and its phase 3 results are still being published as of October 2026. No head-to-head retatrutide vs tirzepatide trial results have been published. In separate placebo-controlled trials of adults with obesity and no diabetes, the reported average weight change was -25.0% on retatrutide 12 mg at 80 weeks (TRIUMPH-1) and -20.9% on tirzepatide 15 mg at 72 weeks (SURMOUNT-1). The trials differ in length, doses and participants, so the numbers can’t be compared one to one.
This page reports what published trials measured. It is not medical advice and not a prediction for any one person. PrescribedRX does not offer retatrutide.
Is retatrutide available?
No. Retatrutide is an investigational drug, and its trials are funded by Eli Lilly (TRIUMPH-1). It is not available by prescription. The TRIUMPH phase 3 program has started to publish results, and more phase 3 results are still being published as of October 2026.
Tirzepatide is sold as Zepbound. The Zepbound prescribing information lists its use for weight reduction in adults with obesity, or overweight with at least one weight-related condition, alongside diet and physical activity (Zepbound prescribing information).
How are retatrutide and tirzepatide different?
Both are once-weekly injections studied for weight loss. The trial papers describe a difference in how many hormone receptors each acts on.
| Retatrutide | Tirzepatide | |
|---|---|---|
| Receptors it acts on | GIP, GLP-1 and glucagon (three) | GIP and GLP-1 (two) |
| Availability | Investigational; not available | Prescription drug, sold as Zepbound |
| Main obesity trials | Phase 2 (2023); TRIUMPH phase 3 program | SURMOUNT phase 3 program |
| Weekly doses in the phase 3 trials below | 4 mg, 9 mg, 12 mg | 5 mg, 10 mg, 15 mg |
| Head-to-head trial | No published results as of October 2026 | |
Sources: retatrutide phase 2, TRIUMPH-1, SURMOUNT-1, Zepbound prescribing information.
What did the trials report?
The table pairs trials in people without diabetes, then trials in people with type 2 diabetes. Numbers are the average percent change in body weight reported in each publication.
| Trial | Who was studied | Length | Average weight change |
|---|---|---|---|
| TRIUMPH-1 (retatrutide) | 2,339 adults with obesity, no diabetes | 80 weeks | -17.6% (4 mg), -23.7% (9 mg), -25.0% (12 mg) vs -3.9% (placebo) |
| SURMOUNT-1 (tirzepatide) | 2,539 adults with obesity or overweight, no diabetes | 72 weeks | -15.0% (5 mg), -19.5% (10 mg), -20.9% (15 mg) vs -3.1% (placebo) |
| TRIUMPH-2 (retatrutide) | 1,152 adults with obesity or overweight and type 2 diabetes | 80 weeks | -11.9% (4 mg), -16.8% (9 mg), -18.8% (12 mg) vs -5.1% (placebo) |
| SURMOUNT-2 (tirzepatide) | 938 adults with obesity or overweight and type 2 diabetes | 72 weeks | -12.8% (10 mg), -14.7% (15 mg) vs -3.2% (placebo) |
Sources: TRIUMPH-1, SURMOUNT-1, TRIUMPH-2, SURMOUNT-2. Tirzepatide trials studied branded tirzepatide, not a compounded product.
What did TRIUMPH-1 and SURMOUNT-1 report?
TRIUMPH-1 is a phase 3 obesity trial of retatrutide, published online in the New England Journal of Medicine on September 29, 2026. Its authors reported that the 9 mg and 12 mg groups lost 19.8 and 21.0 percentage points more than placebo at 80 weeks (Jastreboff et al., NEJM 2026).
SURMOUNT-1 tested tirzepatide for 72 weeks, including a 20-week dose-escalation period. The authors reported that 50% of the 10 mg group and 57% of the 15 mg group lost 20% or more of their body weight, compared with 3% on placebo (Jastreboff et al., NEJM 2022). Our tirzepatide results by timepoint page covers the other SURMOUNT trials, including what happened when people stopped.
What did the phase 2 retatrutide trial report?
The 2023 phase 2 trial enrolled 338 adults with obesity, or overweight with a weight-related condition, for 48 weeks (Jastreboff et al., NEJM 2023). The authors reported:
| Group | Week 24 | Week 48 | Lost 15% or more by week 48 |
|---|---|---|---|
| Retatrutide 1 mg | -7.2% | -8.7% | Not reported |
| Retatrutide 4 mg | -12.9% | -17.1% | 60% |
| Retatrutide 8 mg | -17.3% | -22.8% | 75% |
| Retatrutide 12 mg | -17.5% | -24.2% | 83% |
| Placebo | -1.6% | -2.1% | 2% |
The 48-week phase 2 numbers and the 80-week TRIUMPH-1 numbers come from different trials with different doses.
Has anyone compared them head to head?
Not in published form. As of October 2026, no trial comparing retatrutide directly with tirzepatide has published results. Every “tirzepatide vs retatrutide” comparison, this one included, sets separate trials side by side.
Why can’t you compare the numbers directly?
- Different lengths. The TRIUMPH trials above ran 80 weeks; SURMOUNT-1 and SURMOUNT-2 ran 72 weeks.
- Different doses. Retatrutide was tested at 4, 9 and 12 mg; tirzepatide at 5, 10 and 15 mg.
- Different participants and placebo results. Placebo groups lost 3.9% in TRIUMPH-1 and 3.1% in SURMOUNT-1, and 5.1% in TRIUMPH-2 compared with 3.2% in SURMOUNT-2.
Both main obesity papers report a treatment-regimen estimand, which counts participants whether or not they stopped treatment (TRIUMPH-1, SURMOUNT-1). That makes the method more alike, but not the trials.
What side effects did the trials report?
In every trial on this page, the authors reported that the most common adverse events were gastrointestinal.
- Retatrutide phase 2: GI events were dose-related, mostly mild to moderate, and partly reduced with a lower starting dose (2 mg vs 4 mg). Heart rate rose with dose, peaked at 24 weeks and then declined (Jastreboff et al., 2023).
- TRIUMPH-2: diarrhea occurred in 27% to 34% of the retatrutide groups vs 13% on placebo, and nausea in 14% to 28% vs 8%. Low blood pressure (1% to 6% vs under 1%) and dysesthesia (4% to 7% vs 1%) were also more frequent with retatrutide. Permanent discontinuation due to adverse events or death was 4% (4 mg), 12% (9 mg) and 8% (12 mg), vs 5% on placebo (Bellido et al., 2026).
- SURMOUNT-1: GI events were mostly mild to moderate and occurred mainly during dose escalation. Adverse events led to stopping treatment in 4.3%, 7.1% and 6.2% of people on 5, 10 and 15 mg, vs 2.6% on placebo (Jastreboff et al., 2022).
Retatrutide has no prescribing information because it is investigational. For tirzepatide, see side effects listed in the Zepbound prescribing information.
When should you call a doctor on tirzepatide?
The Zepbound prescribing information and Medication Guide tell patients to contact their healthcare provider, or get medical help, if they notice any of these (Zepbound prescribing information):
- Severe stomach pain that will not go away, with or without nausea or vomiting, sometimes felt in the back (possible pancreatitis)
- Pain in the upper stomach, fever, yellowing of the skin or eyes, or clay-colored stools (possible gallbladder problems)
- Swelling of the face, lips, tongue or throat, trouble breathing or swallowing, severe rash, fainting or a very rapid heartbeat (serious allergic reaction)
- Dizziness, sweating, shakiness, confusion or a fast heartbeat if you also use insulin or a sulfonylurea (low blood sugar)
- A lump or swelling in the neck, hoarseness, trouble swallowing or shortness of breath
The Zepbound prescribing information also tells patients to inform all their healthcare providers before surgery or procedures with anesthesia or deep sedation. Zepbound carries a boxed warning: its prescribing information reports that tirzepatide caused thyroid C-cell tumors in rats, and it is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or MEN 2. Our tirzepatide safety information page covers the rest.
Can you get retatrutide today?
No. Retatrutide is investigational and not available as a prescription medication, and its phase 3 results are still being published as of October 2026. PrescribedRX does not offer retatrutide.
The SURMOUNT trials studied branded tirzepatide. Compounded tirzepatide is a different product; see what compounded tirzepatide is.
How does tirzepatide work with PrescribedRX?
Compounded tirzepatide is offered through PrescribedRX. Compounded medications are prepared by licensed pharmacies and are not FDA-approved. You start with a short online eligibility check. A licensed provider reviews your answers, typically within 48 hours, and decides whether it is appropriate for you. If a prescription is issued, a licensed partner pharmacy fills it. It is self-pay with no insurance, shipping is free priority, and availability varies by state. Your provider sets the dose. For background on how tirzepatide doses are described, see our tirzepatide dosage chart.
- Compounded tirzepatide: 3 month plan $597 · $199/mo · Billed every 3 months. Cancel anytime.
See the compounded tirzepatide plan for what each shipment includes, the tirzepatide cost breakdown, our tirzepatide vs semaglutide trial comparison, or all weight loss treatments.
Sources
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. PubMed. Accessed Oct 2026.
- Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity (TRIUMPH-1). N Engl J Med. 2026, online ahead of print Sept 29, 2026. PubMed. Accessed Oct 2026.
- Bellido V, le Roux CW, Ekinci EI, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. Lancet. 2026;408(10563):1455-1472. PubMed. Accessed Oct 2026.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PubMed. Accessed Oct 2026.
- Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). Lancet. 2023;402:613-626. PubMed. Accessed Oct 2026.
- DailyMed. Zepbound (tirzepatide) injection prescribing information and Medication Guide, revised 08/2026. National Library of Medicine, NIH. dailymed.nlm.nih.gov. Accessed Oct 2026.
This article is for general information. It is not medical advice and it is not a recommendation for any particular treatment. Whether a treatment is appropriate for you is a decision for a licensed clinician who has reviewed your health history and current medications.
About the author
Juan MontesJuan Montes writes and reviews PrescribedRX's clinical content, covering testosterone replacement therapy, men's sexual health, weight management and hair loss. He trained as a Professional Nurse at the Colombian Red Cross in Cali, Colombia, and has worked in healthcare since 2011, roughly six of those years in direct emergency and critical care nursing. He served as Head Nurse in Emergency…
More from Juan →This article is for information only and is not medical advice. Treatment is prescribed solely at the discretion of a licensed provider following a clinical evaluation.
