In plain terms: Retatrutide shows early signals in human research but the evidence is limited -- small trials, surrogate endpoints, or not yet independently replicated. It is an emerging area, not yet a proven one.
Retatrutide
The evidence as the record states it
Jastreboff et al. (New England Journal of Medicine, 2023; PMID 37366315): phase 2, double-blind, placebo-controlled, 338 adults with obesity, 48 weeks. Pre-specified primary endpoint was percentage change in body weight at 24 weeks and it was met: -7.2% to -17.5% across doses versus -1.6% on placebo, reaching -24.2% at 48 weeks on 12 mg. Rosenstock et al. (Lancet, 2023; PMID 37385280): phase 2, 42 US centers, adults with type 2 diabetes, primary endpoint change in HbA1c at 24 weeks, with dulaglutide as an active comparator. Bajaj et al. (Lancet, 2026; PMID 42250575), TRANSCEND-T2D-1: phase 3 in people with type 2 diabetes inadequately controlled on diet and exercise. This is the first phase 3 to report in the peer-reviewed literature. Its endpoints are glycemic and anthropometric, not clinical events. Lilly has also announced topline results from TRIUMPH-1, TRIUMPH-2 and TRIUMPH-3 by press release; those are not peer-reviewed publications and EBL does not grade on them. Every reported endpoint across all of these is body weight or HbA1c rather than a clinical event. Weight loss in obesity rests on one phase 2 trial, and the compound is not approved anywhere: under the single-trial rule that is a C. It rises to B when a second trial in the same population reports in the peer-reviewed literature, and cannot reach A until a trial powered for clinical outcomes reports and is replicated. Moved from B in October 2026 by editor adjudication. TRANSCEND-CKD and the wider TRIUMPH program are registered and had not reported clinical-event endpoints as of this review.
Why Grade C and not Grade B
Grade C reflects early or limited human evidence -- small trials, surrogate endpoints, or preliminary findings not yet independently replicated. The evidence points in a promising direction but does not yet meet the standard for Grade B. A single well-powered, independently replicated trial with a meaningful endpoint would move this to Grade B or higher.
What would move this grade
A well-powered randomized trial with an objective, clinically meaningful primary endpoint and at least one independent replication would support Grade B or higher.
How this was studied
Retatrutide subcutaneously once weekly at 1, 4, 8 or 12 mg with staged escalation, for 48 weeks in the phase 2 obesity trial and 36 weeks in the type 2 diabetes trial. Phase 2 doses only; no phase 3 regimen has been established.