Retatrutide vs Zepbound: What's the Difference?

Q: 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.

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 made by the same company and given as weekly injections. Retatrutide adds a third receptor (glucagon) that increases energy expenditure, producing approximately 6 percentage points more weight loss than Zepbound.

For the detailed comparison, see Retatrutide vs Tirzepatide (Zepbound).

Quick Comparison

	Retatrutide	Zepbound (Tirzepatide)
Receptors	GLP-1 + GIP + Glucagon (triple)	GLP-1 + GIP (dual)
Max weight loss	-28.7% at 68 weeks (12 mg)	-22.5% at 72 weeks (15 mg)
FDA status	Not approved (Phase 3)	Approved (November 2023)
Also sold as	No brand name yet	Mounjaro (for type 2 diabetes)
Monthly cost	Not available (~$1,200–1,500 projected)	~$1,060/month
Discontinuation (AEs)	18.2%	10.5%
Unique side effect	Dysesthesia (20.9%)	Gallbladder/biliary risk

Why Retatrutide Produces More Weight Loss

Zepbound targets two receptors: GLP-1 (appetite suppression) and GIP (metabolic efficiency). Retatrutide targets all three, adding glucagon receptor activation which:

Increases resting energy expenditure through thermogenesis
Promotes breakdown of stored fat, particularly liver fat
Adds a "burn more" mechanism on top of the "eat less" effect

This is why retatrutide achieves ~29% weight loss vs Zepbound's ~22.5%.

Weight Loss Thresholds

Threshold	Retatrutide 12 mg	Zepbound 15 mg
Lost at least 15%	83.2%	73%
Lost at least 20%	72.5%	63%
Lost at least 25%	58.6%	39.7%

For a 250-lb person: retatrutide produces approximately 16 more pounds of weight loss than Zepbound (~72 lbs vs ~56 lbs).

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. Primary completion is December 2026, with results expected to follow in 2027. This will provide the first definitive head-to-head comparison.

Availability

	Retatrutide	Zepbound
Available now	No — clinical trials only	Yes — by prescription
Expected availability	Q4 2027 – Q1 2028	Available since Nov 2023
Insurance coverage	N/A	Growing — check with your plan

Frequently Asked Questions

Is retatrutide replacing Zepbound?

No. Lilly is developing both drugs for different patient needs. Zepbound is available now with strong efficacy and an established safety profile. Retatrutide will be the option for patients seeking maximum weight loss or those with conditions where the glucagon mechanism adds specific benefit (e.g., fatty liver disease).

Should I wait for retatrutide or start Zepbound now?

If you qualify for Zepbound, starting now is reasonable. Retatrutide won't be available until late 2027 at the earliest. Talk to your doctor about your options.

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

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: Retatrutide and similar peptides are investigational — not approved by the FDA or any regulator. Semaglutide and tirzepatide are prescription-only medicines, available only through a licensed prescriber.
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.

Sources