How to Inject Retatrutide: What the Trials Record

"How to inject retatrutide" is searched as if there were instructions to read. There are none. Retatrutide has no label, so nothing written by a regulator says where it goes, how often, or what to do after a missed week. What does exist is a set of trial records, and one of them is exactly the study this search is asking about: Lilly tested the injection sites. This page reports what those records say, what is still unpublished, and the trial doses converted to syringe units. It describes; it gives no instruction.

The dose figures themselves, with the TRIUMPH results, are on the retatrutide dosage page; the label-backed equivalents of this page for the approved molecules are where to inject tirzepatide and where to inject semaglutide. General subcutaneous technique for any peptide is on the peptide injection guide.

The route: subcutaneous, in every arm that states one

A search of ClinicalTrials.gov on 2026-10-02 for retatrutide or its code LY3437943 returned 33 records, from single-dose safety studies to the 10,000-person cardiovascular outcomes trial. The route reads the same almost everywhere:

The schedule is as uniform as the route. Every phase 2 and phase 3 arm read is once weekly. The phase 2 obesity trial's posted participant groups (NCT04881760) describe the escalations directly: 2 mg rising to 4 mg; 2 mg to 4 mg to 8 mg; 4 mg to 8 mg; and 2 mg through 4 and 8 to 12 mg, each "administered as SC injection QW". The phase 2 diabetes trial (NCT04867785, Lancet 2023) was double-dummy because its comparator, dulaglutide, came in a single-dose pen and retatrutide did not. Both trials' ladders arm by arm, with the phase 3 steps Lilly describes and each rung in units, are tabled on the retatrutide dosing schedule.

The injection-site study that has not reported

Lilly did run the study that would answer "where": NCT05959096, titled Effect of Injection Site on the Relative Bioavailability of a Single Dose of LY3437943 in Healthy Participants With a High Body Mass Index.

That is a reportable fact in itself. The approved weekly molecules each carry a label sentence on site — "similar exposure" in the abdomen, thigh and upper arm for both tirzepatide and semaglutide — and those sentences rest on studies of exactly this kind. For retatrutide the study exists, finished more than two years ago, and its answer is not public. A page that ranks injection sites for retatrutide is reporting something nobody outside Lilly can check yet.

A second completed record, NCT06003465, compared retatrutide given by a "test device (test formulation)" with a "reference device (reference formulation)" in 57 healthy participants, primary completion 2024-02-08. The registry describes neither device and has no posted results. It shows a delivery device under development; it does not show what that device is.

What the half-life implies, and what it does not

The only published half-life is "approximately 6 days", from the phase 1b trial in type 2 diabetes (NCT04143802; Urva et al., Lancet 2022), set out with its arithmetic on the retatrutide half-life page. On that figure about 79% of a dose remains two days later and about 45% after a week (arithmetic by this site). The approved weekly labels build their missed-dose windows on similar numbers — four days for tirzepatide, five for Ozempic — but those windows are each label's own rule. With no retatrutide label, no missed-dose window or day-change rule exists for it, and borrowing another molecule's is a guess.

The trial doses in units, research vials

Units on a U-100 syringe = mg ÷ mg/mL × 100. Research vials are labelled 5, 10 and 20 mg; a 10 mg vial with 1 mL is 10 mg/mL, with 2 mL 5 mg/mL. Volumes for each vial size are on retatrutide reconstitution.

At 5 mg/mL every dose from 6 mg upward exceeds one 100-unit syringe, and at 10 mg/mL so does 12 mg. The concentration, not the dose, decides whether a trial step fits in one draw. The milligram-to-units conversion sets out the formula, mg to mL the volumes, and the calculator's retatrutide setting works any vial.

What is not established

Everything a label would normally settle: whether the injection site changes exposure (studied, unreported), which device Lilly intends (studied, undescribed), a missed-dose window, a rule for changing the weekly day, and how a lyophilised research vial compares with the trial formulation, which no record describes. The trial doses on this page describe what was given to trial participants under protocol; they are not a schedule for anyone else. Storage and the general mixing procedure are covered on Medibact's how to store peptides and how to reconstitute peptides pages, and the compound itself in Medibact's Retatrutide guide. Nothing on this page is an instruction; technique and dose belong with a prescriber or a trial protocol.

Sources and dates

Opened 2026-10-02: the ClinicalTrials.gov API search for retatrutide (33 records) and the full records of NCT05959096, NCT06003465, NCT05929066 (TRIUMPH-1), NCT04881760 (posted participant groups) and NCT07629401; PubMed E-utilities search for retatrutide or LY3437943 with injection site or bioavailability (2 records, neither reporting NCT05959096) and the abstract of Rosenstock et al., Lancet 2023 (PMID 37385280). The approval timing and half-life are as recorded on this site's retatrutide dosage and half-life pages. Units and percentages are arithmetic by this site. Corrections go to the contact page.