Retatrutide vs tirzepatide
Tirzepatide targets GIP and GLP-1 receptors; retatrutide also targets the glucagon receptor. Zepbound is an approved tirzepatide medicine, while retatrutide remains investigational in the cited FDA notice. Retatrutide’s 2026 trial headlines are not a head-to-head comparison with Zepbound.
Mechanism, status and evidence
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| Question | Tirzepatide / Zepbound | Retatrutide |
|---|---|---|
| Receptor targets | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Source for US product status | Current Zepbound prescribing information | FDA unapproved-GLP-1 notice |
| Approved product in this comparison | Zepbound injection | None identified by the cited FDA notice |
| Research record to open | Clinical studies in the label | TRIUMPH-1: NCT05929066 |
| What the source establishes | Specific labelled uses and safety information | A trial programme, not a retail medicine approval |
Where the 28.3% headline comes from
Lilly’s 21 May 2026 TRIUMPH-1 report gives 28.3% weight loss at 80 weeks for the 12 mg research arm versus 2.2% for placebo under its efficacy analysis. Its treatment-regimen analysis, which includes outcomes regardless of adherence, gives 25.0% versus 3.9%. These are sponsor-reported trial estimates, not personal forecasts or results against tirzepatide. Reported adverse effects included nausea, diarrhoea and vomiting; the source gives their rates.
What is Zepbound approved for?
The cited US label covers adult weight management under its eligibility criteria and moderate-to-severe obstructive sleep apnea in adults with obesity, alongside diet and physical activity. It also states that coadministration with other tirzepatide products or any GLP-1 receptor agonist is not recommended.
What does the retatrutide trial record add?
TRIUMPH-1 gives an identifiable study to follow instead of a seller’s summary. Its registered title concerns retatrutide in people with obesity or overweight. Trial registration establishes the study’s identity, not approval, availability from a clinic or a guaranteed outcome.
Are they a stack?
The Zepbound label does not recommend combining it with another GLP-1 receptor agonist. A comparison page is not a combination protocol. Product approval and the evidence for taking two substances together are separate questions.
Use the table and its sources
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Source-linked editorial synthesis, prepared with AI assistance. This is not a clinician review or a personalised treatment recommendation. Corrections: editorial standards.