Research guide / Comparison

Retatrutide vs Tirzepatide: What the Research Actually Shows.

Updated September 2026 · 12 minute read

Retatrutide and tirzepatide are two Eli Lilly research molecules with overlapping but different receptor activity. This guide compares their published evidence, registered trials, safety findings, and regulatory status — and explains why trial numbers from different studies cannot simply be ranked against each other.

Research information only. This article summarises published and registered research. It is not medical advice, a dosing guide, or evidence that either molecule is approved for treatment. Trial averages do not predict an individual outcome.

01 / Overview

Retatrutide vs tirzepatide at a glance

Tirzepatide (LY3298176) is a dual GIP/GLP-1 receptor agonist approved in the United States as Mounjaro for type 2 diabetes in May 2022 and as Zepbound for chronic weight management in November 2023. Retatrutide (LY3437943) is a triple agonist that additionally targets the glucagon receptor — and it remains investigational: no regulator has approved it for any use.[11], [12]

Both are once-weekly subcutaneous molecules developed by Eli Lilly, and both have large obesity trial programmes. Beyond that, their evidence bases differ in trial phase, duration, population, and comparator — which is why this guide separates peer-reviewed results from sponsor-reported topline announcements.[13]

If you are comparing the two as laboratory reference materials, each product listing should be read together with the evidence and regulatory distinctions below.

View the Retatrutide research listing View the Tirzepatide research listing

02 / Mechanisms

Two molecules, different receptors

The clearest structural difference is receptor activity. Tirzepatide activates two receptor families; retatrutide activates three. The table reflects laboratory pharmacology as described in the trial publications, not proven human mechanisms.[1], [2], [3]

Receptor activity	Tirzepatide (dual agonist)	Retatrutide (triple agonist)
GIP receptor	Activated	Activated
GLP-1 receptor	Activated	Activated
Glucagon receptor	Not targeted	Activated
US regulatory status	Approved (Mounjaro, Zepbound)	Investigational; not approved by any regulator

The “dual” and “triple” labels describe laboratory pharmacology. They do not by themselves predict outcomes, and the contribution of each receptor pathway to the human results cannot be separated within these trials and should not be treated as settled.

03 / Direct comparison

Has there been a head-to-head trial?

As of this September 2026 update, no head-to-head trial of retatrutide versus tirzepatide has published results. The closest is TRIUMPH-5 (NCT06662383): a Phase 3, randomised, double-blind study of retatrutide compared with tirzepatide in adults with obesity, estimated at about 800 participants, with percent change in body weight at week 80 as the primary outcome. The registry record lists primary completion in November 2026, and results are not yet available.[5]

Until those results are published, any “which is stronger” comparison is indirect. It draws on trials that differ in design, population, duration, and statistical analysis. Cross-trial comparisons can generate hypotheses, but they cannot establish that one molecule is superior to the other.

04 / Trial evidence

What the trials show

The published results for each molecule come from trials with different comparators, durations, and populations. They are measurements within each trial — not measurements against each other.

Tirzepatide’s pivotal diabetes trial, SURPASS-2, randomised 1,879 adults with type 2 diabetes in a 40-week, open-label Phase 3 study against semaglutide 1 mg — not against retatrutide. Mean body-weight change was −12.4 kg (−13.1%) with tirzepatide 15 mg versus −6.2 kg (−6.7%) with semaglutide, and mean HbA1c change was −2.30 versus −1.86 percentage points.[1]

Tirzepatide’s pivotal obesity trial, SURMOUNT-1, randomised 2,539 adults with obesity or overweight without diabetes to 72 weeks of tirzepatide or placebo. Mean body-weight change at week 72 was −15.0%, −19.5%, and −20.9% with 5 mg, 10 mg, and 15 mg, versus −3.1% with placebo.[2]

Retatrutide’s obesity evidence begins at Phase 2: 338 adults with obesity or overweight without diabetes, randomised for 48 weeks. Mean body-weight change at week 48 reached −24.2% at 12 mg versus −2.1% with placebo; the primary endpoint at 24 weeks was −17.5% versus −1.6%. This is a smaller, shorter Phase 2 study — a different tier of evidence from a pivotal Phase 3 trial.[3]

Trial	Phase	Population	Duration	Key reported result	Source type
SURPASS-2	3	Type 2 diabetes · 1,879 participants	40 weeks	Tirzepatide 15 mg −13.1% vs semaglutide 1 mg −6.7%	Peer reviewed
SURMOUNT-1	3	Obesity/overweight without diabetes · 2,539	72 weeks	Tirzepatide 15 mg −20.9% vs placebo −3.1%	Peer reviewed
Retatrutide Phase 2	2	Obesity/overweight without diabetes · 338	48 weeks	Retatrutide 12 mg −24.2% vs placebo −2.1%	Peer reviewed
TRIUMPH-1	3	Obesity or overweight · 2,335 registered	80 weeks	Retatrutide 12 mg −28.3% vs placebo −2.2%	Sponsor topline
TRIUMPH-2	3	Type 2 diabetes with obesity/overweight · 1,152	80 weeks	Retatrutide 12 mg −20.8% vs placebo −4.0%	Sponsor topline
TRIUMPH-3	3	Severe obesity with cardiovascular disease · 1,946 registered	80 weeks	Retatrutide 12 mg −22.6% vs placebo −3.2%	Sponsor topline
TRIUMPH-5	3	Obesity · retatrutide vs tirzepatide · est. 800	80 weeks	Not yet available	Registered, ongoing

Registry records can change; statuses and enrolment figures reflect the original ClinicalTrials.gov records reviewed for this update. Lilly’s announcements and the registry sometimes give different enrolment figures for the same trial; each figure is cited as its source reports it.[6], [7], [8]

Lilly has also announced Phase 3 topline results for retatrutide. In May 2026 it reported TRIUMPH-1 (12 mg: −28.3% at 80 weeks versus −2.2% for placebo, efficacy estimand). On 23 July 2026 it reported TRIUMPH-2 (type 2 diabetes with obesity or overweight: −20.8% at 12 mg versus −4.0%) and TRIUMPH-3 (severe obesity with established cardiovascular disease: −22.6% at 12 mg versus −3.2%). The company said it plans to submit a US marketing application in the first quarter of 2027.[9], [10]

Why these numbers cannot be ranked: the trials used different comparators (semaglutide versus placebo), durations (40, 48, 72, and 80 weeks), populations, trial phases, and statistical estimands. A larger percentage in one trial does not establish superiority over another molecule tested in a different trial.

Shop Retatrutide pen Shop Tirzepatide pen

05 / Safety evidence

Safety findings in trials

Tirzepatide has approved prescribing information in the United States, which regulators reviewed before approval. In its published trials, the most common adverse events were gastrointestinal and primarily mild to moderate. In SURPASS-2, gastrointestinal events were similar to semaglutide, but adverse events causing study withdrawal were more frequent with tirzepatide 10 mg and 15 mg. In SURMOUNT-1, adverse events led to treatment discontinuation in 4.3–7.1% of tirzepatide groups versus 2.6% with placebo.[1], [2]

Retatrutide has no approved prescribing information, so its safety profile rests on trial reports. In the Phase 2 obesity trial, gastrointestinal events were most common, dose-related, and mostly mild to moderate; the paper also reported dose-dependent heart-rate increases that peaked at week 24 and then declined. In the TRANSCEND-T2D-1 Phase 3 trial, discontinuation due to adverse events occurred in 2–5% of retatrutide groups versus 0% with placebo.[3], [4]

Neither molecule’s trials answer every long-term safety question, and no head-to-head safety comparison exists yet — it would need the kind of direct study TRIUMPH-5 is designed to provide. Adverse-event findings depend on the studied population, follow-up period, and controlled trial conditions.

06 / Regulators

Approval status in the US, Europe, and UAE

United States

Tirzepatide is FDA-approved as Mounjaro for type 2 diabetes (13 May 2022) and as Zepbound for chronic weight management (8 November 2023). Retatrutide is not approved: FDA’s current statement on unapproved GLP-1 drugs says retatrutide is not a component of an FDA-approved drug and has not been found safe and effective for any condition. Lilly has said it plans a US submission in the first quarter of 2027 — a company statement, not a regulatory decision.[11], [12], [13]

European Union

The EMA issued a paediatric investigation plan decision for retatrutide in September 2024. A paediatric plan is a development requirement, not a marketing authorisation. This guide makes no EU determination for either molecule’s marketing status; regional approvals should be confirmed with the EMA directly.[13]

United Arab Emirates

The Emirates Drug Establishment maintains the UAE’s public registered medical product directory. We did not identify retatrutide-specific public decisions in the official material reviewed for this update. Directory presence or absence is not used here to infer approval, non-approval, legality, availability, or permission for use for either molecule; those questions require confirmation from the EDE.[14]

07 / Quick answers

Frequently asked questions

Which one causes more weight loss?

No published head-to-head trial answers this. Retatrutide’s Phase 2 numbers (−24.2% at 48 weeks) are larger than tirzepatide’s Phase 3 SURMOUNT-1 numbers (−20.9% at 72 weeks), but the trials differ in phase, duration, size, and analysis — so this is not a valid comparison. The ongoing TRIUMPH-5 study compares them directly.

Is tirzepatide an approved medicine?

Yes, in the United States: Mounjaro was approved for type 2 diabetes in May 2022 and Zepbound for chronic weight management in November 2023. Approvals are jurisdiction-specific, so regional status should be confirmed with the relevant regulator.

Is retatrutide approved anywhere?

No approval should be inferred from clinical research. The FDA source cited here describes retatrutide products as unapproved and not found safe and effective for any condition. Lilly has announced it plans a US marketing application in the first quarter of 2027; that is a sponsor statement, not an approval.

What is TRIUMPH-5?

A Phase 3, randomised, double-blind trial of retatrutide versus tirzepatide in adults with obesity (NCT06662383), estimated at about 800 participants, with percent change in body weight at week 80 as the primary outcome. Its registry record lists primary completion in November 2026; results have not been published at the time of this update.

Can I compare the trial numbers in this guide directly?

No. The trials differ in comparator, duration, population, phase, and statistical estimand. Each row in the comparison table is accurate within its own trial; ranking rows against each other would be misleading.

What does the UAE directory show?

It is a public register of medical products. This guide does not turn a directory search result — or the absence of one — into a claim about approval, legality, or permitted use for either molecule. The Emirates Drug Establishment is the appropriate authority for a current determination.

08 / Sources