Retatrutide vs tirzepatide:
what each trial measured.

The receptors

Tirzepatide agonises GLP-1 and GIP. Retatrutide agonises GLP-1, GIP and glucagon. Glucagon receptor agonism is associated with energy expenditure and hepatic fat handling rather than with appetite, so it is an addition of a different kind rather than more of the same.

The evidence, which is the part that is usually skipped

• Tirzepatide — approved products with Prescribing Information, and phase 3 obesity data (SURMOUNT-1, PMID 35658024). Where a label exists it governs; this site does not.
• Retatrutide — phase 2 dose-ranging in adults with obesity over 48 weeks (PMID 37385275). No approved product, no label, no phase 3 obesity readout.

A phase 2 dose-ranging study exists to find out what doses do. It is not a recommendation and its figures are not a schedule. Quoting a percentage from one beside a percentage from a phase 3 trial treats them as the same kind of claim, and they are not.

What a cross-trial comparison cannot tell you

Different trials enrol different populations, run different durations, and define their endpoints differently. Percentages lifted from two separate studies and placed side by side produce a number that no study produced. It is the single most common error in compound comparisons, and it is invisible once the two figures are in the same table.

The honest statement is narrower and still useful: retatrutide's phase 2 results were strong enough to justify phase 3, and that is a statement about a research programme rather than about what either compound will do for a given person.