Retatrutide vs Tirzepatide: How the Two Compare

Retatrutide and tirzepatide are both injectable, once-weekly incretin-based medicines developed by Eli Lilly, but they are at very different stages. Tirzepatide is already approved and sold as Mounjaro (type 2 diabetes) and Zepbound (obesity). Retatrutide is still investigational and not approved by the FDA. This guide compares what is publicly known about each, so you can understand the difference the next time the two come up.

Important: Retatrutide is not FDA-approved and is not available by prescription. Everything below is general educational information drawn from published trials and company statements, not medical advice.

What is the difference between retatrutide and tirzepatide?

The headline difference is the number of receptors each drug targets. Tirzepatide is a dual agonist that activates the GLP-1 and GIP receptors. Retatrutide is a triple agonist that activates GLP-1, GIP, and, additionally, the glucagon receptor. The glucagon component is thought to increase energy expenditure, which researchers believe may contribute to the large weight reductions seen in early retatrutide trials.

Side-by-side comparison

Retatrutide: the investigational triple agonist

Retatrutide is a synthetic peptide that activates three receptors with a single molecule. In its Phase 2 obesity trial, published in the New England Journal of Medicine, the 12 mg once-weekly dose produced a mean weight reduction of about 24.2% at 48 weeks, with roughly a quarter of participants on the top dose losing more than 30% of their body weight. It has a half-life of roughly 6 days, which supports once-weekly dosing, and Phase 2 doses studied were 1, 4, 8, and 12 mg weekly.

Retatrutide is now in the large Phase 3 TRIUMPH program. Topline Phase 3 results have since been reported (TRIUMPH-4 in late 2025 and TRIUMPH-1 in 2026), and they continued to show large weight reductions, with TRIUMPH-1 reporting about 28.3% mean weight loss at the 12 mg dose over 80 weeks. Even so, the drug remains investigational while Lilly completes its program and prepares a regulatory submission. As of 2026 it is not FDA-approved and not available by prescription, and any product sold as "retatrutide" outside of a clinical trial is not an FDA-approved medicine.

Tirzepatide: the approved dual agonist

Tirzepatide is FDA-approved and widely prescribed. It is marketed as Mounjaro for type 2 diabetes and Zepbound for chronic weight management. It is given as a once-weekly subcutaneous injection, typically started at a low dose (2.5 mg) and escalated over time under a provider's direction. In its obesity program it produced substantial weight loss, and in the head-to-head SURMOUNT-5 trial it outperformed semaglutide.

Because tirzepatide is approved, its dosing, escalation schedule, and safety information are established in FDA labeling. Only a licensed healthcare provider can determine whether it is appropriate for a given person.

Which causes more weight loss?

In its Phase 2 trial, retatrutide produced numerically larger weight reductions than those typically reported for tirzepatide in obesity trials. However, this is not a fair head-to-head comparison. The trials had different designs, durations, and populations, and retatrutide's Phase 3 program is still ongoing. No approved medicine can be compared to an investigational one as if both were on the market. What matters clinically will only be clear once retatrutide's full Phase 3 data and any regulatory review are complete.

Are the side effects similar?

Both are incretin-based drugs, and the most common adverse events reported in trials of each are gastrointestinal (nausea, diarrhea, vomiting, and constipation), mostly during dose escalation. Retatrutide's Phase 2 data also noted a dose-dependent increase in heart rate that peaked around 24 weeks. Because retatrutide is investigational, its full safety profile is still being characterized in Phase 3.

Can I get retatrutide instead of tirzepatide?

No. Retatrutide is not approved and cannot be prescribed as an approved medicine. Only tirzepatide (and other approved GLP-1 medicines) can currently be prescribed. If you are interested in either, that is a conversation to have with your healthcare provider, who can explain approved options and, if relevant, clinical-trial participation.

Medical Disclaimer

This page is general educational information, not medical advice. Retatrutide is investigational and not FDA-approved. Trial figures are reported as published in the referenced studies and do not represent dosing recommendations. RetaPal is a private tracking and reminder app only. It does not recommend, calculate, or suggest doses. Always follow the dose and schedule provided by your own prescriber, and consult your healthcare provider before starting, stopping, or changing any medication.

If you and your provider have decided on a regimen, RetaPal can help you log each weekly dose and count down to your next injection, privately and offline, without ever suggesting a dose itself.