"Retatrutide vs tirzepatide" is mostly asked as a question about strength. The searches that follow it — dose, dosage chart, which is better — show that the practical question is how the two dose ladders line up. They do not line up neatly, and this page shows why: one ladder comes from a label, the other from trial arms, and the milligram figures on each belong to a different molecule. Nothing here ranks the drugs or recommends a dose.
The molecules themselves — the third receptor, what each is thought to do, the full trial record — are compared on Medibact's Tirzepatide vs Retatrutide page. The single-molecule figures are on the tirzepatide dosage page and the retatrutide dosage page. The same layout against the GLP-1-only ladder is on retatrutide vs semaglutide.
Status first: one label, one pipeline
| Tirzepatide | Retatrutide | |
|---|---|---|
| Receptors | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Approval | ZEPBOUND (obesity, sleep apnoea) and MOUNJARO (type 2 diabetes) | None; Eli Lilly stated on 2026-07-23 that it plans to file in the first quarter of 2027 |
| Where the doses come from | The label, section 2 | Trial registrations and publications |
| Half-life | About 5 to 6 days (ZEPBOUND label) | About 6 days (phase 1b, PMID 36354040) |
| Top weekly dose in the record | 15 mg (label maximum) | 12 mg (highest trial arm) |
The half-lives are close enough that both are injected once a week and both take about a month to reach a steady level; the ZEPBOUND label states steady state after 4 weeks of weekly dosing. The clearance arithmetic for each is on tirzepatide's half-life page and retatrutide's half-life page.
The two ladders side by side
Tirzepatide's ladder is fixed by its label: 2.5 mg for four weeks, then 5 mg, then 2.5 mg steps no sooner than every four weeks, with 5, 10 and 15 mg as maintenance dosages. The label adds that 2.5 mg "is for treatment initiation and is not approved as a maintenance dosage".
Retatrutide's ladder is whatever each trial registered. The phase 2 obesity trial (NCT04881760) ran six active arms:
| Phase 2 arm (48 weeks) | Escalation as registered |
|---|---|
| 1 mg | 1 mg from the start |
| 4 mg (2 mg start) | 2 mg, then 4 mg |
| 4 mg (4 mg start) | 4 mg from the start |
| 8 mg (2 mg start) | 2 mg, 4 mg, then 8 mg |
| 8 mg (4 mg start) | 4 mg, then 8 mg |
| 12 mg (2 mg start) | 2 mg, 4 mg, 8 mg, then 12 mg |
The publication reports that gastrointestinal events were dose-related and "partially mitigated with a lower starting dose (2 mg vs. 4 mg)". The phase 3 TRIUMPH programme moved to a 2 → 4 → 6 → 9 → 12 mg ladder with four-week steps, according to Lilly's 2026 releases as recorded on this site's retatrutide page.
Read across, the ladders cross at odd places. Retatrutide's 1 mg arm has no tirzepatide counterpart below 2.5 mg; its 4 mg arm sits between tirzepatide's 2.5 and 5 mg; its 12 mg top sits under tirzepatide's 15 mg ceiling. None of these crossings means the doses are equivalent.
What each ladder produced, in its own trial
| Trial | Dose | Weight change | Placebo | Duration |
|---|---|---|---|---|
| Retatrutide phase 2 (PMID 37366315) | 1 / 4 / 8 / 12 mg | -8.7% / -17.1% / -22.8% / -24.2% | -2.1% | 48 weeks |
| SURMOUNT-1, tirzepatide (PMID 35658024) | 5 / 10 / 15 mg | -15.0% / -19.5% / -20.9% | -3.1% | 72 weeks |
These two rows are the reason milligrams cannot be traded across molecules: 8 mg of retatrutide produced a larger mean change in 48 weeks than 10 mg of tirzepatide did in 72. They are also the reason the rows cannot rank the drugs: 338 adults against 2,539, different durations, different enrolment rules. A Lilly release on TRIUMPH-2, listed on its press-release index when read on 2026-10-01, (adults with obesity and type 2 diabetes) reports 20.8% average loss on 12 mg over 80 weeks — a third population, again not comparable to either row.
The trial that will compare them
NCT06662383 is a phase 3, randomised, double-blind trial of retatrutide against tirzepatide in 800 adults with obesity. It started on 1 November 2024, its primary outcome is percent change in body weight at week 80, and the registry (last updated 2026-07-20) lists primary completion as November 2026, estimated. Participants are randomised to one drug or the other; nobody in it switches. Until it reports, every "which is stronger" answer is built from separate trials. Moving from one drug to the other is a different question, covered on switching from tirzepatide to retatrutide.
Both ladders in syringe units
Units on a U-100 syringe = mg ÷ mg/mL × 100. Research vials of tirzepatide are commonly labelled 10, 15 and 30 mg and of retatrutide 5, 10 and 20 mg; the concentration depends on the water added.
| Tirzepatide step | 5 mg/mL | 10 mg/mL | 20 mg/mL |
|---|---|---|---|
| 2.5 mg | 50 units | 25 units | 12.5 units |
| 5 mg | 100 units | 50 units | 25 units |
| 7.5 mg | 150 units | 75 units | 37.5 units |
| 10 mg | 200 units | 100 units | 50 units |
| 15 mg | 300 units | 150 units | 75 units |
| Retatrutide arm or step | 5 mg/mL | 10 mg/mL | 20 mg/mL |
|---|---|---|---|
| 1 mg | 20 units | 10 units | 5 units |
| 2 mg | 40 units | 20 units | 10 units |
| 4 mg | 80 units | 40 units | 20 units |
| 8 mg | 160 units | 80 units | 40 units |
| 12 mg | 240 units | 120 units | 60 units |
Anything over 100 units exceeds a 1 mL syringe. The approved tirzepatide products avoid unit arithmetic altogether: every single-dose pen and vial holds its strength in 0.5 mL, so the concentration rises from 5 mg/mL (2.5 mg) to 30 mg/mL (15 mg) while the volume stays at 50 units. A unit count carried from one of those products, or from one molecule's vial to the other's, is a different number of milligrams. The formula and its common misreadings are on converting milligrams to syringe units; the calculator's tirzepatide and retatrutide settings work any vial.
What is not established
No dose equivalence between retatrutide and tirzepatide exists in any label, trial or pharmacology paper. The head-to-head trial has not reported. Retatrutide has no label, so no regulator has set its starting dose, steps or maximum. GLP1Ledger's retatrutide vs tirzepatide comparison covers the two as medicines; this page stays with the figures. Nothing here is a dose, a switch or a plan.
Sources and dates
Opened 2026-10-01: the ZEPBOUND label via openFDA (Eli Lilly, effective 2026-08-28), sections 2, 3 and 12.3; ClinicalTrials.gov v2 records NCT06662383 and NCT04881760 (arms and status); PubMed abstracts PMID 37366315 (retatrutide phase 2), 35658024 (SURMOUNT-1) and 36354040 (retatrutide phase 1b); Lilly's press-release index (TRIUMPH-2 summary). The TRIUMPH escalation and the filing date as recorded on this site's retatrutide dosage page from Lilly's releases of 2026-05-21 and 2026-07-23. Units are arithmetic by this site. Corrections go to the contact page.