Empowering Medical Aesthetic Clinics, Practitioners, and Patients

Retatrutide vs Tirzepatide: a Quick Comparison Guide

Last updated: September 2026

With advances in obesity and diabetes treatment, two medications — retatrutide and tirzepatide — sit at the front of the field. They belong to the same family of incretin-based drugs, but they are not at the same stage: tirzepatide is FDA-approved and prescribed every day, while retatrutide is still investigational. The retatrutide vs tirzepatide comparison has changed considerably in 2026, and this guide reflects where it stands as of September.

Three phase 3 retatrutide trials reported between December 2025 and July 2026, and a head-to-head trial comparing the two drugs directly is due to finish in December 2026. Below we compare how each one works, what the trials actually measured, how the side effects differ, and what each drug has proven beyond weight loss. If you are looking for dosing specifically, our retatrutide dosage guide covers the phase 3 step-up schedule in detail.

Key Takeaways

Is Retatrutide More Effective Than Tirzepatide?

The honest answer, as of September 2026, is that nobody knows yet — and anyone who tells you otherwise is comparing two different trials. Both drugs are multi-action hormonal medications that target the pathways regulating blood glucose and body weight, but they have never been tested against each other in a published study.

What we can compare is what each drug did in its own pivotal obesity trial. On those numbers, retatrutide is ahead. In the 80-week TRIUMPH-1 trial, participants on the 12 mg dose lost an average of 28.3% of their body weight. In the 72-week SURMOUNT-1 trial, participants on the top 15 mg dose of tirzepatide lost 22.5%.

The Head-to-Head Trial: TRIUMPH-5

A phase 3 trial called TRIUMPH-5 is comparing retatrutide directly against tirzepatide in adults with obesity. It enrolled roughly 800 participants, its main measurement is the percentage of body weight lost at week 80, and it is double-blind, meaning neither participants nor investigators know which drug someone is receiving.

The trial began in November 2024 and is no longer recruiting. Its scheduled completion is December 2026, so results should become public in late 2026 or during 2027. That is the study that will settle the question this page asks, and it is worth watching for anyone advising patients on which direction the field is heading.

Why the Usual Comparison Overstates the Gap

Weight-loss trials report two versions of the same result. One describes what happened to people who stayed on treatment as intended. The other describes what happened to everyone who was assigned the drug, including those who stopped early. The first number is always larger.

Most online comparisons quote retatrutide’s “stayed on treatment” figure against tirzepatide’s “everyone assigned” figure, which makes the gap look bigger than it is. Compared consistently, the difference is roughly 4 to 6 percentage points.

Both trials enrolled adults with obesity, or overweight plus a weight-related condition, without diabetes. Neither trial included the other drug. Sources: Eli Lilly and Company, May 21, 2026; June 4, 2022.

How Is Retatrutide Different?

The difference between these two medications is the number of hormone receptors each one activates. Tirzepatide is a dual agonist: it acts on the GIP and GLP-1 receptors, reducing appetite, slowing stomach emptying, and improving the body’s insulin response. Retatrutide does all of that and adds a third target, the glucagon receptor.

That third receptor is the entire reason retatrutide is a different kind of drug. Glucagon-receptor activation is thought to increase energy expenditure and mobilize fat stored in the liver, which is the leading explanation for the larger weight-loss figures seen in its trials. In a phase 2a liver study, 89% of participants on 8 mg and 93% on 12 mg reached a normal liver-fat level by 48 weeks.

A note on “GLP-3”: there is no drug class by that name. It is internet shorthand for a medication acting on three receptors instead of one or two.

Retatrutide vs Tirzepatide: Weight Loss

Weight loss is the reason most people compare these two drugs, and both produce far more of it than earlier treatments did. The chart below lines up the doses studied in each drug’s pivotal obesity trial, using the same measure for both: average weight loss among people who stayed on treatment.

TRIUMPH-1 (retatrutide, 80 weeks) and SURMOUNT-1 (tirzepatide, 72 weeks), efficacy estimand. Separate trials with different participants; the doses are lined up for reference, not as a direct comparison.

Two details matter when quoting these figures. First, the headline number belongs to the top dose only — retatrutide’s lowest studied maintenance dose, 4 mg, landed between tirzepatide’s 5 mg and 10 mg results. Second, retatrutide’s highest doses carried the highest discontinuation rates, so the best-tolerated dose and the highest-loss dose are not always the same.

Depth of response is where the difference is clearest. In TRIUMPH-1, 45.3% of participants on 12 mg lost 30% or more of their body weight, a range previously associated with bariatric surgery, compared with 0.5% on placebo. Among 532 people who continued to 104 weeks, average loss reached about 30.3%.

Results in People With Type 2 Diabetes

Weight loss is consistently smaller when a patient has type 2 diabetes, and that holds for both drugs. Retatrutide averaged 20.8% at 12 mg over 80 weeks in the TRIUMPH-2 trial of participants with type 2 diabetes, compared with 28.3% in participants without it. Tirzepatide shows the same pattern across its own program, so this is a familiar counseling point rather than a surprise.

What the Earlier Phase 2 Study Showed

The figures many articles still quote come from retatrutide’s 48-week phase 2 obesity trial, published in the New England Journal of Medicine: average losses of 22.8% on 8 mg and 24.2% on 12 mg. Those results were what prompted the phase 3 program, which has now reported and supersedes them. Note that 8 mg was dropped in phase 3 in favor of 9 mg.

Retatrutide vs Tirzepatide: Side Effects

The safety stories are more similar than different. Both drugs are dominated by gastrointestinal effects that increase with dose and cluster during dose escalation, which is why both use a gradual step-up schedule. The ranges below cover all doses studied in each pivotal trial.

Ranges across the doses studied: retatrutide 4, 9, and 12 mg; tirzepatide 5, 10, and 15 mg. Sources: Eli Lilly and Company, 2026 and 2022.

What Is Dysesthesia?

Dysesthesia means an unusual or unpleasant skin sensation — tingling, burning, or sensitivity to touch. It was not a prominent finding with tirzepatide or semaglutide, which makes it the most distinctive safety signal in the retatrutide program so far. Lilly reports these events were generally mild to moderate and that most resolved during treatment. Retatrutide’s phase 2 trial also showed a dose-related rise in heart rate.

The Difference That Matters Most Clinically

Tirzepatide’s risks are characterized: large completed trials, years of real-world use, an FDA-approved label, and the class boxed warning regarding medullary thyroid carcinoma. Retatrutide’s profile is still being defined, and rarer or longer-term effects only become visible as a program completes. That asymmetry — known versus not yet known — is as important as any percentage on this page.

What Each Medication Has Proven Beyond Weight Loss

Average weight loss is one measure. What a drug has been shown to do for health outcomes is another, and here the picture reverses.

Sources: New England Journal of Medicine, December 2025; Eli Lilly and Company, 2025–2026; FDA approval records.

Retatrutide vs Tirzepatide vs Semaglutide

Many readers are really asking a three-way question, because semaglutide is the drug most patients started on. The progression is straightforward: one receptor, then two, then three.

Figures come from separate trials except SURMOUNT-5, which compared tirzepatide and semaglutide directly. For a closer look at the two approved options, see our Zepbound® vs Wegovy® comparison.

The category moved in other ways in 2026 as well. A higher-dose semaglutide injection, Wegovy® HD (7.2 mg), was approved in March 2026 with 20.7% average weight loss over 72 weeks, and Foundayo™ (orforglipron), the first GLP-1 pill that can be taken without food or water restrictions, was approved in April 2026. Patients comparing options today have more approved choices than at any point in this drug class’s history.

FDA Status, Availability and the Gray Market

This is the difference that matters most in practice today, and it is worth stating plainly.

• Tirzepatide is approved and available. It is prescribed as Zepbound® for chronic weight management and as Mounjaro® for type 2 diabetes, with established dosing covered in our tirzepatide dosage guide.
• Retatrutide is not approved anywhere. Eli Lilly plans to submit its FDA application in the first quarter of 2027, and approval could only follow once the FDA completes its review.
• A regulatory classification question is unresolved. Lilly and the FDA disagree over whether retatrutide should be regulated as a biologic. This affects the type of application and the exclusivity period, not the safety message.
• Early access is narrow. In August 2026 Lilly formalized an early access program for a limited number of patients who meet specific medical criteria and cannot enroll in a trial. Physicians submit the request to Lilly.
• Enforcement against online sellers is active. On August 24, 2026 the FDA issued a warning letter to an online seller marketing “GLP-3 Reta,” classifying its products as unapproved new drugs and rejecting the “research use only” label as a defense. Four patient-safety organizations issued a joint warning about black-market retatrutide the same month. Our retatrutide warning for GLP-1 providers covers the liability and sourcing risks in detail.

There is no legitimate compounded version of retatrutide, because compounding pharmacies may not compound a drug the FDA has never approved. Any vial sold as retatrutide today is outside the regulated supply chain.

What to Tell Patients Asking to Switch

Patients are asking about retatrutide long before they can receive it, often while doing well on an approved medication. A consistent answer protects both the patient and the practice:

• Be direct about status. It is not approved, it cannot be prescribed, and a filing is not expected until early 2027.
• Do not pause effective treatment to wait. Weight regain after stopping an incretin medication is well documented, and the wait here is measured in years, not weeks.
• Name the legitimate routes. A clinical trial listed on ClinicalTrials.gov, or Lilly’s early access program, are the only lawful ways to receive it today.
• Address the gray market plainly. “Research” vials are unapproved and unverified, and dosing them involves guesswork that no clinician can supervise safely.
• Optimize what is available. Many patients asking about retatrutide have not yet reached the top tolerated dose of their current medication, or have not had their plateau, nutrition, and muscle-preservation plan reviewed.

How the Two Dosing Schedules Compare

Retatrutide doses are shown for clinical context only. No dose of retatrutide is approved, and it should never be self-administered.

The clinical skills involved are the same in both columns: patient selection, gradual titration, side-effect management, and monitoring. A practice that runs semaglutide and tirzepatide well is already prepared for whatever is approved next. You can sample IAPAM’s clinical GLP-1 training with the free 1-CME module below.

Free Online GLP-1 Training · Earn 1 CME

Try GLP-1 training free.
Earn 1 CME on us.

Get self-paced access to a real IAPAM provider module covering GLP-1 and GIP receptor agonists, clinical protocols, and patient safety, and claim 1 AMA PRA Category 1 CME™ when you finish. It’s a free sample of our Certified Medical Weight Management Provider™ (CWMP™) program.

What’s Inside Your Free Module

GLP-1 & GIP Receptor AgonistsVideo lectures

Clinical ProtocolsDownloadable resources

Patient SafetyBest practices

1 AMA PRA Cat 1 CME™On completion

Full Module Value$79 — Free

Eligibility: MD/DO, NP, PA, RN

Get Your Free GLP-1 Training + 1 CME

Enter your details and we’ll email your access link.

Frequently Asked Questions

Is retatrutide better than tirzepatide?

In their own trials retatrutide has produced larger average weight loss: 28.3% at 12 mg over 80 weeks in TRIUMPH-1, compared with 22.5% at 15 mg over 72 weeks for tirzepatide in SURMOUNT-1. Those are separate trials with different participants, so they are not a direct comparison. Tirzepatide is also approved, prescribable, and backed by cardiovascular outcome data, while retatrutide is investigational. “Better” depends on whether the question is average weight loss in a trial or a treatment a patient can actually receive today.

Have retatrutide and tirzepatide been compared head-to-head?

Not yet in published results. A phase 3 head-to-head trial called TRIUMPH-5 is comparing retatrutide directly against tirzepatide in about 800 adults with obesity, measuring percentage of body weight lost at week 80. It began in November 2024, is no longer recruiting, and is scheduled to complete in December 2026, so results are expected in late 2026 or 2027. Until then, every comparison between the two drugs is a comparison across separate trials.

Is retatrutide FDA approved?

No. As of September 2026 retatrutide is investigational and is not approved by the FDA for any use. Eli Lilly has said it plans to submit its application in the first quarter of 2027, and approval could only follow once the FDA completes its review. Tirzepatide, by contrast, is approved as Mounjaro® for type 2 diabetes and as Zepbound® for chronic weight management and obstructive sleep apnea.

What is “reta,” and why do people call it GLP-3?

“Reta” is shorthand for retatrutide, and “GLP-3” is an informal nickname that appears in online discussion. GLP-3 is not a real drug class and no medication is called GLP-3. The nickname comes from retatrutide acting on three receptors rather than one or two. The official development code is LY3437943.

How do retatrutide and tirzepatide compare with semaglutide?

Semaglutide, sold as Wegovy® and Ozempic®, acts on the GLP-1 receptor alone and produced about 15% average weight loss in its pivotal obesity trial, with the higher-dose 7.2 mg version approved in March 2026 reaching 20.7%. Tirzepatide adds the GIP receptor and beat semaglutide head-to-head in SURMOUNT-5, 20.2% against 13.7% over 72 weeks. Retatrutide adds a third receptor, glucagon, and has produced the largest trial figures so far, but it is not approved.

Can a patient switch from tirzepatide to retatrutide?

No. Retatrutide cannot be prescribed or dispensed because it is not approved. The only lawful routes are a clinical trial or Eli Lilly’s limited early access program for patients who cannot enroll in a trial. Stopping an effective approved medication while waiting for an unapproved one usually means regaining weight, and products sold online as “research use” retatrutide are unapproved drugs of unverified identity, strength, and sterility.

Are the side effects worse with retatrutide than tirzepatide?

Both are dominated by gastrointestinal effects that rise with dose and cluster during escalation. In their pivotal trials, nausea was reported by 28.6% to 42.4% of retatrutide participants compared with 24.6% to 33.3% on tirzepatide, and 4.1% to 11.3% of retatrutide participants stopped because of side effects compared with 4.3% to 7.1% on tirzepatide. Retatrutide also showed dysesthesia, an unusual skin sensation such as tingling or burning, in 5.1% to 12.5% of participants, which was not a prominent finding with tirzepatide.

Conclusion

Tirzepatide is FDA-approved for weight loss under the brand name Zepbound®, while retatrutide remains investigational, with an FDA filing planned for the first quarter of 2027. On trial numbers the triple agonist is ahead: 28.3% average weight loss at 12 mg over 80 weeks, against 22.5% for tirzepatide at its top dose. On everything else — approved uses, cardiovascular outcome data, real-world safety experience, and the simple fact that a patient can start it tomorrow — tirzepatide is the one with the record.

The question this page asks gets a real answer when TRIUMPH-5, the head-to-head trial, completes in December 2026. Until then, the most useful preparation for any practice is fluency with the medications available now. 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.

Explore GLP-1 Certification Training →

References

1. Eli Lilly and Company. (2022, June 4). SURMOUNT-1 tirzepatide results published in the New England Journal of Medicine [Press release].
2. Eli Lilly and Company. (2025, December 11). Retatrutide TRIUMPH-4 phase 3 results [Press release].
3. Eli Lilly and Company. (2026, May 21). Retatrutide TRIUMPH-1 phase 3 results [Press release].
4. Eli Lilly and Company. (2026, July 23). Retatrutide TRIUMPH-2 and TRIUMPH-3 phase 3 results [Press release].
5. Jastreboff, A. M., et al. (2023). Triple–hormone-receptor agonist retatrutide for obesity: A phase 2 trial. New England Journal of Medicine, 389(6), 514–526.
6. Sanyal, A. J., et al. (2024). Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: A randomized phase 2a trial. Nature Medicine, 30(7).
7. Nicholls, S. J., et al. (2025, December 17). Cardiovascular outcomes with tirzepatide versus dulaglutide in type 2 diabetes (SURPASS-CVOT). New England Journal of Medicine.
8. U.S. National Library of Medicine. TRIUMPH-5: retatrutide compared with tirzepatide (NCT06662383). ClinicalTrials.gov.
9. U.S. Food and Drug Administration. (2026, August 24). Warning letter: Peptide Partners LLC.

Safety Advisory: Retatrutide remains an investigational agent under study and is not approved by the FDA or other major regulatory authorities for 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.