Retatrutide for Weight Loss (Research-Reported)

TL;DR

- In the phase 2 trial, participants on the highest retatrutide dose showed a mean body weight change of about 24.2 percent at 48 weeks (Jastreboff et al., 2023). - Retatrutide is a single molecule that acts on three receptors: GLP-1, GIP, and glucagon (Jastreboff et al., 2023). - Retatrutide is investigational. It has no marketing approval and is studied only in clinical trials as of this writing (Jastreboff et al., 2023). - Reported reductions were dose-dependent, with lower studied doses producing smaller mean changes than 12 mg (Jastreboff et al., 2023). - After stopping GLP-1-class therapy, published data on related agents report meaningful weight regain, so durability is a separate question (Wilding et al., 2022; Aronne et al., 2024).

What does the trial report on retatrutide and weight loss?

The phase 2 trial reported a mean body weight change of up to about 24.2 percent at 48 weeks in the highest-dose group (Jastreboff et al., 2023).

This came from a randomized, double-blind, placebo-controlled phase 2 study of adults with obesity, published in the New England Journal of Medicine (Jastreboff et al., 2023, doi:10.1056/NEJMoa2301972). The trial tested several dose levels against placebo. The largest mean reduction, about 24.2 percent, was seen in the 12 mg group at week 48. This figure is a group mean from a trial, not a promise of any individual result. Retatrutide remains investigational, and the numbers here describe what researchers measured, not an outcome you should expect.

For context within the same drug class, semaglutide showed about 15 percent mean weight loss in STEP 1 (Wilding et al., 2021), and tirzepatide reached up to about 22.5 percent in SURMOUNT-1 (Jastreboff et al., 2022).

How does retatrutide work in the body?

Retatrutide is a triple agonist that activates the GLP-1, GIP, and glucagon receptors with one molecule (Jastreboff et al., 2023).

The first two targets, GLP-1 and GIP, are incretin pathways shared with tirzepatide, which is a dual GLP-1 plus GIP agonist (Jastreboff et al., 2022). Retatrutide adds a third arm: glucagon receptor activity. Glucagon signaling is linked to energy expenditure and hepatic fat handling, which is the proposed reason for adding it to an incretin backbone. The phase 2 paper describes this three-receptor design as the mechanistic basis for the reported changes (Jastreboff et al., 2023). Human evidence beyond phase 2 is still limited, so longer-term mechanism-to-outcome data are not yet established.

What dose levels did the research report?

The trial studied several fixed dose levels, with the largest mean weight change at 12 mg (Jastreboff et al., 2023).

The table below lists the dose levels named in the phase 2 publication. These are research-reported figures from a trial, not instructions. Any decision about a personal dose belongs with a qualified clinician.

Values are approximate group means as reported in the phase 2 paper (Jastreboff et al., 2023). Different dose-escalation schedules were used within the trial design; the publication is the primary source for those details.

Is retatrutide approved or still investigational?

Retatrutide is investigational and has no marketing approval; it has been studied in clinical trials only (Jastreboff et al., 2023).

The 2023 publication describes phase 2 results, an earlier stage than the large phase 3 programs that supported approval of other agents in this class. Because it is investigational, there is no approved label, no approved indication, and no established real-world safety profile outside trial conditions. Anything described on this page reflects trial reporting, not guidance for use.

How does retatrutide compare to tirzepatide and semaglutide?

Across separate trials, the reported peak mean weight change was highest for retatrutide, then tirzepatide, then semaglutide, though these came from different studies and cannot be directly compared head to head.

These figures come from different trial designs, populations, and durations, so the grid shows reported ranges, not a controlled comparison. A direct head-to-head trial would be needed to compare them properly. One such head-to-head between tirzepatide and semaglutide exists (Frias et al., 2021, SURPASS-2), but retatrutide has not been compared to them in the same study.

What happens to weight after stopping this drug class?

Published data on related GLP-1-class agents report meaningful weight regain after treatment stops (Wilding et al., 2022; Aronne et al., 2024).

In the STEP 1 extension, participants regained a large share of lost weight after semaglutide was withdrawn (Wilding et al., 2022). SURMOUNT-4 reported weight regain after tirzepatide was stopped (Aronne et al., 2024). This pattern is consistent with adaptive thermogenesis, the body's tendency to defend a higher weight after loss (Rosenbaum and Leibel, 2010). Retatrutide-specific withdrawal data are limited given its investigational stage, so durability remains an open question.