Retatrutide vs Tirzepatide
A weekly weight-loss injection not yet approved. In trials people lost up to about a quarter of their body weight in 48 weeks. It is the weekly shot behind Mounjaro and Zepbound, used for diabetes and weight loss. Large trials show 15% to 21% weight loss.
Tirzepatide has the stronger evidence, grade A (strong human evidence) against grade B for Retatrutide. Retatrutide: In clinical trials. Tirzepatide: FDA approved.
Evidence
BSome human evidence
AStrong human evidence
Human studies cited
Animal or cell studies cited
Why the grade
There is one published randomized phase 2 trial in obesity (338 adults, 48 weeks), a 98-person liver fat substudy of that trial, and one published phase 3 trial, TRIUMPH-2, in 1,152 adults with obesity and type 2 diabetes over 80 weeks; other phase 3 results exist only as press releases. Multiple randomized trials point the same way, but the drug is not approved, most of the roughly 5,800-person TRIUMPH program is unpublished, and there is no long-term safety data, so the grade is B and not A.
Tirzepatide's weight-loss use rests on the SURMOUNT program of randomized placebo-controlled trials, the largest being SURMOUNT-1 with 2,539 adults, plus trials in type 2 diabetes, sleep apnea, weight maintenance and diabetes prevention. Every approved indication was granted on randomized data, so it grades A.
FDA
In clinical trials
Retatrutide is an investigational drug and is not approved by the FDA for any use. Eli Lilly has said it plans to file for approval in the first quarter of 2027 after completing manufacturing data. Vials sold online as retatrutide are not a legal product; the FDA has stated that unapproved GLP-1 class drugs cannot be used in compounding.
FDA approved
Tirzepatide is approved by the FDA as Mounjaro (2022) for type 2 diabetes in adults, extended to children 10 and older and to cardiovascular risk reduction in adults with type 2 diabetes and established cardiovascular disease, and as Zepbound (2023) for chronic weight management and for moderate to severe obstructive sleep apnea in adults with obesity.
Sold for
Retatrutide is talked about as the next step beyond tirzepatide, a triple-hormone injection that produced the largest weight loss yet seen in a drug trial.
Tirzepatide is the weight-loss injection that outperformed semaglutide, cutting body weight by about a fifth in trials.
Studies say
Randomized trials show about a quarter of body weight lost over 48 weeks and roughly a fifth over 80 weeks in people with diabetes, with gastrointestinal side effects and heart rate increases, which supports a B pending approval and full phase 3 publication.
Multiple large randomized trials show weight loss of 15 to 21 percent, better glucose control than other diabetes drugs, and improvement in sleep apnea, with weight regain after stopping, which is a clean A.
Class
Triple GLP-1 / GIP / glucagon agonist
Dual GIP + GLP-1 receptor agonist
Route
Injection
Injection