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Editorially reviewed · Last updated September 8, 2026 · How we review

Retatrutide vs Zepbound: What's the Difference?

Part of Weight Loss Drug Comparison Index.

Retatrutide vs Zepbound: What's the Difference?

Zepbound is the brand name for tirzepatide, Eli Lilly's FDA-approved dual agonist (GLP-1 + GIP) for obesity. Retatrutide is Lilly's investigational triple agonist (GLP-1 + GIP + Glucagon) currently in Phase 3 trials.
Both are given as weekly injections, but they are different molecules. Retatrutide has produced larger average weight-loss results in some separate trials; a direct advantage over Zepbound has not been established. For someone considering treatment now, the main distinction is that Zepbound is approved and retatrutide is investigational.
For the detailed comparison, see Retatrutide vs Tirzepatide (Zepbound).

Quick Comparison

RetatrutideZepbound (Tirzepatide)
ReceptorsGLP-1 + GIP + Glucagon (triple)GLP-1 + GIP (dual)
Selected trial weight loss-28.7% at 68 weeks (12 mg)-22.5% at 72 weeks (15 mg)
FDA statusNot approved (Phase 3)Approved (November 2023)
Also sold asNo brand name yetMounjaro (for type 2 diabetes)
Monthly costNo approved product or announced priceVaries by coverage, dose and device; see Lilly savings terms
Discontinuation (AEs)18.2% (TRIUMPH-4, 12 mg)6.2% (SURMOUNT-1, 15 mg)
Safety considerationsGI events and dysesthesia in trialsGI events; gallbladder disease and dysesthesia are also in the label

Why Retatrutide Produces More Weight Loss

Retatrutide adds glucagon receptor activity to the GLP-1 and GIP targets shared with tirzepatide. Preclinical research supports effects on energy expenditure and liver fat metabolism, but the clinical trials do not isolate each receptor's contribution. A different receptor profile does not prove superior weight loss in the same patients. Retatrutide liver-fat trial.

Weight Loss Thresholds

ThresholdRetatrutide 12 mgZepbound 15 mg
Lost at least 15%Not stated in the cited TRIUMPH-4 topline release78% (efficacy estimand)
Lost at least 20%Not stated in the cited TRIUMPH-4 topline release63% (efficacy estimand)
Lost at least 25%58.6%Not reported in the cited topline release
The weight-loss results use each trial's efficacy estimand. TRIUMPH-4 followed people with obesity and knee osteoarthritis for 68 weeks; SURMOUNT-1 followed a broader obesity population without diabetes for 72 weeks. These averages cannot predict an extra number of pounds an individual would lose on one drug. TRIUMPH-4, SURMOUNT-1.

The TRIUMPH-5 Head-to-Head Trial

Eli Lilly's TRIUMPH-5 (NCT06662383) is a Phase 3 head-to-head trial of approximately 800 participants comparing retatrutide against tirzepatide (the active ingredient in Zepbound). Status: active, not recruiting. The current registry estimates primary completion in November 2026 and study completion in December 2026; neither date guarantees when results will be published. Trial record. Results will provide a direct comparison within the trial's population and follow-up.

Availability

RetatrutideZepbound
Available nowNo — clinical trials onlyYes — by prescription
Expected availabilityNo approval date established; Lilly plans a Q1 2027 U.S. filingAvailable since Nov 2023
Insurance coverageN/AGrowing — check with your plan

Frequently Asked Questions

Is retatrutide replacing Zepbound?

Retatrutide has not been approved, and its eventual place alongside Zepbound is not established. Zepbound remains an approved treatment. Retatrutide's ongoing trials are testing benefits and risks in obesity and related conditions.

Should I wait for retatrutide or start Zepbound now?

Discuss currently approved options with your clinician. Lilly plans to submit retatrutide for U.S. approval in Q1 2027, but that is not an approval or launch date. The decision to start treatment should reflect your health needs, contraindications, access and preferences. Current Lilly status.

Is Zepbound the same as Mounjaro?

Yes — both are tirzepatide made by Eli Lilly. Zepbound is for obesity/weight loss. Mounjaro is for type 2 diabetes. Same molecule, different brand names for different indications.

Sources

  • U.S. Food and Drug Administration. (2026). Zepbound prescribing information, including dysesthesia in section 6.1. Label.
  • Eli Lilly. (2026). Retatrutide Phase 3 status and planned Q1 2027 submission. Release.
  • Eli Lilly. (2022). SURMOUNT-1 detailed results. Release.
  • Eli Lilly. (2025). TRIUMPH-4 results. Press release.
  • Jastreboff, A.M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). NEJM. DOI: 10.1056/NEJMoa2206038.
  • ClinicalTrials.gov. TRIUMPH-5 (NCT06662383). Lilly Trial Guide.
How we keep this honest
What this is
Educational information, not medical advice. It reports published research — it doesn’t recommend that you use, obtain, or supply anything.
Regulatory status
Zepbound is an FDA-approved prescription medicine. Retatrutide remains investigational and has no approved prescribing label.
Our standard
Every claim traces to a primary source. We label the strength of evidence and flag estimates as estimates — never as clinical fact.
No commercial ties
We don’t sell, supply, or link to suppliers of any medicine, and aren’t affiliated with any manufacturer.

Do not make decisions about your health without consulting a qualified healthcare provider. For trial enrolment, see ClinicalTrials.gov. More on how we review.

Grounded in primary sources
NEJMThe LancetJAMAFDAClinicalTrials.gov

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