Tirzepatide vs retatrutide: what's coming after Mounjaro

TL;DR

• Retatrutide adds a third receptor - glucagon, on top of tirzepatide's GIP and GLP-1 pair, reaching energy expenditure and liver-fat mobilisation.
• TRIUMPH-1 reported about 28% average weight loss at 80 weeks in its top-dose arm, with 45% of that group losing 30% or more.
• Retatrutide is investigational - not approved in any market, with an FDA submission anticipated in early 2027 and the cardiovascular outcomes trial running to 2028–2029.
• No head-to-head against tirzepatide has reported - TRIUMPH-5 expects primary completion around December 2026, but the earliest realistic readout is 2027 or later.
• The league table everyone quotes is a cross-trial comparison - different populations, durations, background care and analysis conventions, not a race.
• Tirzepatide remains the most potent approved option - up to −22.5% in SURMOUNT-1, and −20.2% versus semaglutide's −13.7% in the one genuine head-to-head, SURMOUNT-5.

MAB-reviewed and cleared for the Malaysian market (Jun 2026). Educational content, not medical advice. Compound and trial data lead; retatrutide is investigational and not approved or available - that's stated throughout. Doses appear only as studied. Nothing here is a recommendation to obtain an unapproved drug.

Updated October 2026: clarifies the status box: the four core TRIUMPH obesity trials (1 to 4) have reported, while TRIUMPH-5 (head-to-head against tirzepatide) and TRIUMPH-6 have not.

Updated September 2026 (2): moves the TRIUMPH-5 December 2026 primary-completion date out of this changelog and into the body, comparison table and sources, where readers will actually meet it.

Updated September 2026: re-confirms TRIUMPH-5 has still not read out, and distinguishes its expected primary completion (~December 2026) from an actual readout (2027 or later), a distinction likely to be collapsed in coverage.

Updated August 2026: added the current status of TRIUMPH-5, the first direct head-to-head of investigational retatrutide against tirzepatide - it has not read out, and every retatrutide-vs-tirzepatide figure in this article is now explicitly labelled as a cross-trial comparison.

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If semaglutide works on one gut-hormone receptor and tirzepatide (Mounjaro) works on two, retatrutide - an investigational compound - works on three, adding glucagon to the GIP and GLP-1 pair. That third lever reaches metabolism in ways the others don't, and in May 2026 its first Phase 3 trial, TRIUMPH-1, reported an average of about 28% body weight loss at the top dose over 80 weeks - the highest figure the class has produced. The honest framing up front: retatrutide looks like it may raise the ceiling again, but it is still investigational, not approved, not available, and no head-to-head comparison against tirzepatide has yet reported results. Tirzepatide remains the most potent approved option you can actually access today.

Here's where each one stands.

Looking for the full picture? This page covers a direct head-to-head of two compounds. For how the whole class fits together - single, dual and triple agonists plus the amylin branch, with the 2026 trial data - start with GLP-1 generations compared.

2026 regulatory status. The four core TRIUMPH obesity trials (TRIUMPH-1 to TRIUMPH-4) have now reported; TRIUMPH-5, the head-to-head against tirzepatide, and TRIUMPH-6 have not. Lilly has said it intends to submit retatrutide for FDA review in early 2027. A planned submission is not an approval: retatrutide is investigational and not approved in any market, and the FDA has stated it is not a component of an approved drug and cannot legally be used in compounding. Until an approval is granted, no retatrutide-containing product may legally be sold for human use in the United States. The cardiovascular outcomes trial runs to 2028–2029.

The two at a glance

Read this table sideways, not head-to-head. The two weight-loss figures below come from different trials, run in different populations, over different durations, in different years. They are not a comparison of the two compounds against each other. See What a real head-to-head would settle - and when it arrives below.

Why a third receptor matters

The progression isn't just "more is better" - each receptor adds a distinct mechanism. GLP-1 suppresses appetite and slows gastric emptying. GIP (tirzepatide's addition) improves insulin sensitivity and appears to ease tolerability. Glucagon (the addition in investigational retatrutide) is the interesting one: beyond appetite, glucagon-receptor activation raises energy expenditure and drives liver-fat mobilisation. So retatrutide doesn't just turn appetite down harder - it reaches metabolic levers, particularly around fat burning and the liver, that the dual agonist doesn't touch. That is a mechanistic rationale, not a demonstrated clinical advantage over tirzepatide; the trial that would test it has not reported.

What TRIUMPH-1 actually showed

The Phase 3 data for investigational retatrutide are genuinely striking. In adults with obesity (no diabetes) over 80 weeks, retatrutide produced average weight loss of roughly 19%, 26% and 28% across its three ascending dose arms, with 45% of the top-dose group losing 30% or more - a level historically associated with bariatric surgery. Roughly two-thirds of the top-dose group dropped below the obesity threshold (BMI <30), and in a blinded extension for the most severe-obesity subgroup, weight loss reached about 30% by 104 weeks. It also moved cardiovascular risk factors in the right direction - waist circumference, non-HDL cholesterol, triglycerides, blood pressure and the inflammation marker hs-CRP. A separate trial, TRIUMPH-4, reported large knee-osteoarthritis pain reductions alongside the weight loss in people with obesity and knee OA (relevant to our piece on GLP-1s and joints).

Every one of those numbers describes what happened inside the retatrutide trials. None of them describes retatrutide measured against tirzepatide.

What a real head-to-head would settle - and when it arrives

Status as of 3 September 2026: the head-to-head exists, and it has not read out. One distinction worth holding onto, because it is the likeliest source of a premature headline: TRIUMPH-5's primary completion - the point at which data collection on the primary endpoint finishes - is currently expected around December 2026. That is not the same as a result. Database lock, analysis, and reporting follow, which is why the earliest realistic readout remains 2027 or later. Expect "TRIUMPH-5 completes" coverage in the new year that reads like an answer and isn't one.

TRIUMPH-5 (NCT06662383) is the first direct randomised head-to-head of investigational retatrutide against tirzepatide. It runs approximately 89 weeks, and as of today it is active and closed to new participants. It has not reported results. Its expected primary completion is around December 2026, and the earliest indicated readout is 2027 or later - two different dates for two different events, which coverage will collapse into one. Anyone quoting a "retatrutide beat tirzepatide" result today is not quoting TRIUMPH-5, because TRIUMPH-5 has not produced one.

Why the numbers everyone quotes aren't a comparison

The figures that circulate as a league table - retatrutide ~28.3–28.7%, tirzepatide ~22.5%, semaglutide ~14.9% - come from three separate trials. Lining them up in a row makes them look like a race. They aren't one. In plain English, here's what differs between those trials and why it matters:

• Different people. Each trial recruited its own population. Starting BMI, the proportion with type 2 diabetes, age, sex mix and country all shift the average result - before the drug does anything. A trial that enrols heavier participants tends to report a larger percentage loss.
• Different lengths. 72 weeks, 80 weeks and 68 weeks are not the same measuring stick. Weight loss in this class is still accumulating late in the first year, so a longer trial flatters its drug.
• Different background care. Diet and activity counselling, visit frequency and the intensity of support around the injection vary by protocol, and they contribute real weight loss on their own.
• Different titration and tolerability rules. How fast doses escalate, and how the protocol handles people who can't tolerate the top dose, changes how many participants reach the highest dose the headline number is drawn from.
• Different eras. These trials ran in different years, with different standards of care, different levels of public familiarity with the class, and different dropout patterns. Trial results drift over time even for the same molecule.
• Different analysis conventions. Whether the headline figure is an efficacy estimate (what happened in people who stayed on drug) or a treatment-policy estimate (everyone randomised, regardless of what they did afterwards) can move the number by several percentage points on its own.

Stack those together and a gap of a few percentage points between two trials tells you very little. A randomised head-to-head removes all of it at once: same protocol, same population, same duration, same clinics, participants assigned by chance. That is what TRIUMPH-5 is for, and that is why the only defensible sentence today is we don't yet know.

The one genuine head-to-head this class has produced is tirzepatide vs semaglutide (SURMOUNT-5, −20.2% vs −13.7%). Note how different that is from the cross-trial figures above - same two drugs, smaller apparent gap, because the comparison was actually built to be fair. Nothing equivalent involving retatrutide has reported.

Trial status source: GLP-3 Wiki trial tracker, https://www.glp3.wiki/trials (accessed 20 August 2026).

The honest caveats - and they're big

This is where staying agnostic matters most:

• It's investigational. Retatrutide is not approved by any major regulator, not registered in Malaysia, and not something a legitimate clinic can prescribe. A regulatory submission is anticipated in early 2027; a submission is the start of a review, not the end of one.
• There's no head-to-head result with tirzepatide. Comparing "−28% over 80 weeks" against "−22.5% over 72 weeks" is a cross-trial comparison, not a fair fight - different patients, baseline BMI, durations, background care and eras, as set out above. TRIUMPH-5 is running but has not reported. Its expected primary completion is around December 2026 - and that date is worth holding carefully, because it is the point at which the trial finishes collecting its primary-endpoint data, not the point at which anyone sees a result. Analysis, write-up and reporting follow, so the earliest realistic readout remains 2027 or later. Expect the December date to be reported as though it were a results date; it is not. The only honest head-to-head we currently have in this class is tirzepatide vs semaglutide (SURMOUNT-5), not anything involving retatrutide.
• More potent means more to tolerate. Like the others, retatrutide's side effects in trials were dose-related and predominantly gastrointestinal, and the trial protocols escalated doses gradually under supervision.
• Don't chase it on the grey market. The appearance of striking trial numbers reliably triggers a wave of unregulated "research" versions. An investigational triple agonist obtained from a website carries every grey-market risk - wrong dose, contamination, counterfeit - with even less known about its safety margins. Until any approval, no retatrutide-containing product may legally be sold for human use in the US, and enforcement action against sellers is now active. See Retatrutide expanded access: what it really means.

The landscape is moving fast

Retatrutide isn't the only thing on the horizon. The field is shifting quickly - including toward oral options: orforglipron, a once-daily GLP-1 pill, has moved through late-stage development and regulatory review, which matters for anyone who'd rather not inject. The point isn't to wait for the perfect future drug; it's that this category is evolving rapidly, and the right move is to work with someone who tracks it rather than chasing whichever molecule trended this month.

The bottom line - and where to start

Investigational retatrutide is the most promising thing coming, and its Phase 3 results are real - it may well reset the ceiling. But "coming" is the operative word: it's investigational, unavailable, and still unproven against tirzepatide directly, with the trial designed to settle that question not due to report before 2027 at the earliest. Today, tirzepatide is the most effective option you can actually, safely access, and the smartest position isn't to wait on the sidelines for retatrutide - it's to start with what works now under supervision, with a clinician who'll fold in the next advance when it's actually approved.

Explore it with verified supply. Every Vivre Labs lot is independently tested and the certificate of analysis is published, so you know exactly what is in the vial. Explore Tirzepatide.

Related reading

• Mounjaro vs Wegovy vs Ozempic: the honest comparison - the approved options, compared
• GLP-1s and your joints - the knee-osteoarthritis evidence, including retatrutide's
• Keeping the weight off after you stop - why the molecule is only half the plan
• The four compounds, side by side - all four on one comparison table
• Retatrutide expanded access: what it really means - the access environment, and why it isn't one
• Retatrutide's third receptor - what the glucagon arm actually does

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Educational content, not medical advice. Retatrutide is investigational, not approved, and not available through legitimate channels; it is described here only as research context. Do not obtain investigational or prescription medications from unregulated sellers. Trial figures describe study populations; cross-trial comparisons are not head-to-head, and the head-to-head trial (TRIUMPH-5) has not reported. Individual results vary. Claims for the Malaysian market were reviewed and cleared by MAB (Jun 2026).

Primary references

• Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205–216.
• Aronne LJ, et al. Tirzepatide versus semaglutide (SURMOUNT-5). N Engl J Med. 2025. (−20.2% vs −13.7%, head-to-head)
• Eli Lilly. TRIUMPH-1 Phase 3 topline results (retatrutide), 21 May 2026. (up to ~28% at 80 weeks; ~30% in BMI ≥35 extension to 104 weeks)
• Eli Lilly. TRIUMPH-4 Phase 3 topline results (retatrutide in obesity + knee OA), 11 Dec 2025. (−28.7% weight; large WOMAC pain reduction)
• Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity - a phase 2 trial. N Engl J Med. 2023;389:514–526. (earlier phase 2 basis)
• TRIUMPH-5, NCT06662383 - retatrutide vs tirzepatide, ~89 weeks, active and closed to new participants; expected primary completion ~December 2026; not yet reported, earliest readout 2027 or later. Status via GLP-3 Wiki trial tracker, https://www.glp3.wiki/trials (accessed 20 August 2026).