Compounds compared · 7 min
The honest version of this article is shorter than the ones you will find elsewhere, because the central question — what dose replaces the one you are on — has no published answer. What follows is what is established, and what to do with the fact that the rest is not.
There is no established conversion between these two compounds. Not a ratio, not a percentage, not a starting dose indexed to what you take now. If you find a page giving you one, that number was invented by whoever wrote the page. Retatrutide has no approved human dose in any jurisdiction, so there is nothing for a conversion to be anchored to.
Tirzepatide is a dual agonist: it activates the GLP-1 receptor and the GIP receptor. Retatrutide is a triple agonist — the same two, plus the glucagon receptor.
That third receptor is the whole of the difference, and it is not a stronger version of the first two. Glucagon receptor agonism acts on energy expenditure and hepatic fat metabolism, which is a different mechanism from the appetite and glycaemic effects people associate with GLP-1. It is why the compounds are not interchangeable at any dose, and why “adapted to tirzepatide” does not mean adapted to retatrutide.
Tirzepatide has FDA-approved products and published phase 3 obesity data (SURMOUNT-1, PMID 35658024), with a labelled titration schedule that the Prescribing Information governs. Where an approved label exists, it is the authority on dosing — not this site.
Retatrutide's published human data is phase 2 (PMID 37385275): a 48-week dose-ranging obesity trial in adults, which is a trial designed to find out what doses do, not a guideline. There is no phase 3 obesity readout, no approved product, and no label.
Those two evidence bases are not comparable, and a table putting a tirzepatide dose beside a retatrutide dose implies a correspondence that no study has tested. Nobody has run the trial that would answer it: a head-to-head switching study with a conversion endpoint.
Matt’s instruction for this site is that dose figures are reference, not advice — the same rule the compound library already runs on. These are the schedules the trials and the labels used. They are not indexed to you, and nothing below is a dose to take.
| Tirzepatide — labelled titration | Weekly dose |
|---|---|
| Weeks 1–4 (initiation) | 2.5 mg |
| Weeks 5–8 | 5 mg |
| Then in 2.5 mg steps, no sooner than every 4 weeks | 7.5 → 10 → 12.5 mg |
| Maximum studied in SURMOUNT-1 | 15 mg |
Source: the approved product’s Prescribing Information, and SURMOUNT-1 (PMID 35658024). Where an approved label exists it governs — not this page. The 2.5 mg initiation dose is explicitly a starting dose for tolerance, not a treatment dose.
| Retatrutide — phase 2 dose arms | Weekly maintenance target |
|---|---|
| Arm 1 | 1 mg |
| Arm 2 (two escalation speeds) | 4 mg |
| Arm 3 | 8 mg |
| Arm 4 | 12 mg |
| Placebo | — |
Source: the 48-week phase 2 obesity trial (PMID 37385275). Every arm began at 2 mg weekly and escalated to its target; the 4 mg target was run at two different escalation speeds. These are trial arms — the doses a protocol assigned in order to measure what they did. There is no approved product and no label.
What is deliberately not here, and why. You will find pages giving a table that converts your current tirzepatide dose into a retatrutide starting dose — “on 5 mg, start at 1–1.5 mg”, and so on. No trial has measured that correspondence, so there is no source to attach to such a table and we will not print numbers we cannot source. The two tables above are the real figures either side of that question; what bridges them is a conversation with a prescriber, not arithmetic.
The reasoning you will see is that prior GLP-1/GIP exposure should let you start higher than a naive user. The first half is plausible pharmacology. The second half — therefore this many milligrams — does not follow from it. Tolerance at two receptors says nothing quantitative about a third you have never activated, and the dose-limiting effects in the phase 2 data were not only the ones familiar from GLP-1 agonists.
An argument that gets you to “probably not the naive starting dose” is not an argument that gets you to a figure. The gap between those two is where the invented tables live.
A switch is the one period where your own record is worth more than anyone's protocol, because you are the only person running your particular change. Worth having, dated:
BioHack Track records all of that and will show you the history; it will not tell you what to take. That is deliberate and it is the same reason this article has no dose table.
This is reference, not advice. Nothing here prescribes, diagnoses or recommends, and nothing here is a dose for you. Retatrutide is not an approved medicine; tirzepatide's approved products are governed by their Prescribing Information and by a clinician who knows your history. See the editorial policy for how these figures are sourced.