There is no approved retatrutide dose: the drug is investigational, and Lilly plans to file with the FDA in the first quarter of 2027.[5] In the Phase 2 obesity trial it was injected once weekly at 1, 4, 8 or 12 mg, with higher doses started at 2 or 4 mg;[1] its roughly 6-day half-life is why dosing is weekly.[4]
There is no approved dose of retatrutide, because there is no approved retatrutide. It is an investigational drug — Eli Lilly's once-weekly triple agonist, which has reported Phase 3 results but has not yet been submitted for approval — and it is not cleared for use by any regulator, anywhere.[5] So the honest version of a “dosage guide” is narrow: what can be described is the way the drug was dosed in the trials, not a regimen anyone should replicate at home. For what those trials actually showed on efficacy, start with our retatrutide Phase 2 evidence monograph; this page is about the doses and the titration schedule behind those numbers.
What doses of retatrutide did the trials use?
In the 48-week Phase 2 obesity trial (338 adults), retatrutide was injected subcutaneously once weekly at one of several maintenance doses — 1 mg, 4 mg, 8 mg or 12 mg— against placebo.[1] The 12 mg arm was the top dose tested, and it produced the largest weight loss (about −24.2% at 48 weeks).[1] Those are the doses that generated the headlines. They are also the ceiling of what has been studied: 12 mg is not a “recommended” dose, it is simply the highest maintenance dose the trial evaluated. The Phase 3 TRIUMPH trials kept the same ceiling: TRIUMPH-2 tested 4, 9 and 12 mg weekly, and TRIUMPH-3 tested 9 and 12 mg.[5] How the molecule stacks up against the approved dual agonist is covered in our retatrutide versus tirzepatide comparison.
What is retatrutide's half-life?
About 6 days. In the Phase 1b multiple-ascending-dose trial in people with type 2 diabetes, retatrutide's pharmacokinetics were dose-proportional and its half-life was approximately 6 days, which the investigators said suits once-weekly dosing.[4] Lilly's discovery paper reached the same conclusion from the first single-dose study: the drug's pharmacokinetic profile supported once-weekly injection, and weight stayed below baseline for up to 43 days after a single dose.[3] A 6-day half-life also means a dose change takes several weeks to reach a new steady level, which fits the trials' habit of climbing in steps spaced weeks apart rather than days.
How was retatrutide titrated? Slow escalation
The single most important dosing detail is what the trials did not do — they did not start anyone at 12 mg. Participants began at a low starting dose and were escalated in steps toward their assigned maintenance dose. In the obesity trial the starting doses were 2 mg or 4 mg once weekly, stepped up over the following weeks.[1] The companion Phase 2 type 2 diabetes trial went further, formally comparing “slow” versus “fast” escalation to the same 8 mg maintenance dose, with most arms starting at 2 mg — data the investigators say helped select doses for the Phase 3 program.[2] The staircase in the illustration above is the whole idea: you climb, you do not jump.
Why escalate slowly? The GI-tolerability rationale
Like every incretin-based drug, retatrutide's most common adverse events were gastrointestinal — nausea, vomiting, diarrhea — and they were dose-related.[1] The reason for the slow titration is spelled out directly in the data: GI events were partially mitigated by using a lower 2 mg starting dose instead of 4 mg.[1] Starting low and ramping gives the gut time to adapt before the dose climbs. This is the same pattern seen across the class, and the typical arc of when those symptoms appear and fade is laid out in our GLP-1 GI side-effects timeline. (Worth noting separately: the trials also saw dose-dependent heart-rate increases that peaked around 24 weeks — another reason dosing belongs under clinical monitoring.)[1]
The honest bottom line
Reduced to what the evidence supports: in Phase 2, retatrutide was dosed once weekly by subcutaneous injection, escalated stepwise from a 2–4 mg start up to maintenance doses as high as 12 mg, with the slow ramp there specifically to limit gastrointestinal side effects.[1][2]That is a description of trial conduct, not a prescription. There is no approved dose, no long-term safety verdict, and no legitimate product to dose — so the only defensible “dosage” for retatrutide today is the one used under medical supervision in a clinical study. Any real-world decision belongs with a clinician, not a vendor's label.