Retatrutide vs Mounjaro (tirzepatide) and eloralintide

A side-by-side comparison of Mounjaro (tirzepatide), retatrutide and eloralintide. See how the weight-loss studies differ, which comparisons are direct and what is authorised in the UK.

By Manchester Peptides · Published 24 October 2026 · Updated 5 November 2026

The main difference: three receptor targets versus two

Retatrutide, also called LY3437943, acts at GIP, GLP-1 and glucagon receptors. Tirzepatide acts at GIP and GLP-1 receptors. The additional glucagon-receptor activity is a mechanistic difference; counting receptor targets alone cannot establish which treatment would be safer, more effective or suitable for an individual.

For the individual evidence maps and literature, open the Retatrutide research guide and Tirzepatide research guide. This comparison explains how to read two landmark studies, rather than claiming to review every subsequent trial.

Landmark studies compared

The trial details come from the 2023 Retatrutide paper and the 2022 SURMOUNT-1 paper. Both examined adults with obesity, or overweight with a qualifying weight-related condition, without diabetes. Each paper defines its own eligibility criteria, analysis and follow-up.

Why headline weight-loss percentages are not a league table

For the related GLP-1 mechanism and STEP 1 study context, read the Semaglutide research guide. Semaglutide, tirzepatide and retatrutide are different molecules; the number of receptor targets is not a clinical ranking.

Different studies can use different participants, treatment schedules, follow-up periods and statistical approaches. A result at 48 weeks cannot simply be treated as equivalent to one at 72 weeks. The analysis may also handle people who stop treatment differently.

A fair reading asks: what was measured, when was it measured, how was missing data handled and how uncertain is the estimate? A larger percentage from a separate trial does not, by itself, prove superiority. This is an interpretation of the differences in trial design, not a finding that the two compounds are equivalent.

Our clinical-trial phases guide explains the purpose of each phase. The research-evidence checklist helps separate a published finding from a marketing claim.

Research materials and authorised medicines are different references

The MHRA authorised Mounjaro, a tirzepatide medicine, for adult weight management in November 2023 under specified conditions. That authorisation concerns the assessed medicine and its approved information. It is not an authorisation of every vial or pen carrying the word tirzepatide, nor does it extend to a different molecule.

For current medicine information and safety guidance, consult the MHRA's GLP-1 medicines guidance. This educational page does not recommend a treatment, provide switching instructions or determine suitability for personal use.

What can a certificate of analysis add?

A COA can describe analytical results for the submitted sample identified in the report. It cannot turn a catalogue material into the trial formulation or establish clinical safety and effectiveness. Labelled amount, measured content, chemical identity and clinical evidence answer separate questions.

Use the peptide COA reading guide to check sample identity, methods and measured results. The purity, identity, content and sterility guide explains why one purity figure cannot cover every quality question.

Questions to take back to the original paper

• Was the comparator placebo or another active medicine?
• Did the trial population match the population discussed in the claim?
• Is the figure a primary endpoint, a secondary endpoint or an exploratory result?
• Are discontinuations, adverse events and uncertainty reported alongside benefits?
• Is someone transferring a finding from a controlled trial to an unrelated catalogue sample?

Mounjaro, retatrutide and eloralintide compared

Has retatrutide been tested directly against Mounjaro's active ingredient?

The registered Phase 3 TRIUMPH-5 study compares retatrutide with tirzepatide in adults with obesity. No results from that head-to-head study were located when this guide was updated. Until those data are available, separate trial percentages cannot show how the two compare in the same population and protocol.

What did eloralintide plus tirzepatide show?

Lilly reported a Phase 2b comparison of the investigational EloraTZP combination with tirzepatide alone in adults with type 2 diabetes. That study does not compare eloralintide alone with tirzepatide. It also does not compare either treatment with retatrutide. The eloralintide guide separates the monotherapy and combination results.

Which study answers each comparison question?

How to spot a misleading weight-loss comparison

• Check the starting point. Some trials measure from the first study visit. Others randomise after a lifestyle programme or an initial period on the medicine.
• Match the analysis and time point. A result that assumes continued treatment at 48 weeks answers a different question from one that accounts for stopping treatment at 80 weeks.
• Read the comparator. A placebo comparison establishes a result against placebo under study conditions. A direct comparison is needed to assess how two active treatments performed in the same trial.
• Read the safety outcomes alongside weight loss. Check discontinuations, serious events and follow-up. Results in one population may differ from results in another.