Microdosing Retatrutide Chart: Week-by-Week Dose and IU Reference

What Microdosing Retatrutide Means in Practice

This page is the chart reference. The deep pharmacokinetic theory, interactive schedule embeds, and community evidence live in our full microdosing retatrutide guide. Here, microdosing means one of two things: splitting the weekly dose into two or three injections per week, or starting below the 2mg Phase 2 dose as an off-label sensitivity protocol. Both approaches change the shape of the concentration curve between injections, not the total weekly drug exposure.

How Retatrutide's Half-Life Shapes Split Dosing

Retatrutide's half-life is approximately 6 days (Urva et al., Lancet 2022), between tirzepatide's 5 days and semaglutide's 7 days. That matters for reader expectation. The week-to-week swing on once-weekly retatrutide is already smaller than on once-weekly tirzepatide (modelled peak-to-trough about 1.84 vs 2.25), though larger than on semaglutide (about 1.61). Splitting the dose still produces a real reduction in peak concentration, but the absolute smoothing benefit is more modest than what you would see with a shorter-half-life compound. Net effect: the PK case for splitting retatrutide is weaker than for tirzepatide and somewhat stronger than for semaglutide, and stronger on tolerability grounds when GI side effects are the limiting factor.

Microdosing Retatrutide Chart: Split-Dose Schedules

Each split value below is the Phase 2 titration dose divided by injection frequency. IU values assume 10mg/mL vial concentration, where 1 mL equals 100 IU on a standard U-100 insulin syringe. If your concentration differs, see the retatrutide dosing in units guide for the full standard-dose table.

Twice-weekly split-dose values derived from the Phase 2 retatrutide titration ladder. IU shown at 10mg/mL.

Chart A: Twice-Weekly Split Dose (Monday and Thursday)

The most common split. The Phase 2 weekly dose is divided in two, injected on Monday and Thursday or any 3-to-4-day spacing.

Chart B: Three-Times-Weekly Split Dose (Mon, Wed, Fri)

The same weekly mg split across three injections with 48-hour gaps on weekdays and a 72-hour gap over the weekend. The modelled benefit is smaller than with tirzepatide (about 15% vs 19% lower peak for Mon/Wed/Fri), because tirzepatide's shorter half-life gives splitting more to smooth.

Chart C: Sub-Clinical Microdose Starts (Below 2mg per Week)

Some clinicians begin highly sensitive patients below the 2mg Phase 2 dose. The values below reflect what appears in clinical-practice writing and real-world reports, not trial data. They are shown so you can recognize the range, not as an endorsement of any specific number.

The 2mg row is the boundary between off-label and studied territory. The Phase 2 trial randomized maintenance arms at 1mg, 4mg, 8mg, and 12mg; titration moved 2mg to 4mg every 4 weeks for the higher arms.

How to Read These IU Values

The IU column only works if your vial concentration matches the chart's assumption of 10mg/mL. The formula is:

At 10mg/mL, 1 mL is 100 IU on a U-100 insulin syringe. For the full standard-dose conversion table at multiple concentrations, see retatrutide dosing in units. For vial-specific reconstitution math, see the retatrutide BAC water calculator.

Weekly-Progression Timeline

Once you choose a split schedule, the 4-week hold times stay the same as the Phase 2 ladder. Only the per-injection mg changes. The image below shows the twice-weekly progression: the same week markers from the ladder, but at the per-injection values from Chart A.

Twice-weekly progression showing per-injection mg at each 4-week hold, with IU equivalents at 10mg/mL.

Steady state is still reached at 4 to 5 weeks regardless of how you distribute the weekly dose, because that timeline is driven by the half-life, not the injection schedule. Total weekly exposure is unchanged. What changes is the shape of the curve between injections, not the area under it.

Comparing Retatrutide vs Tirzepatide Split Dosing

Retatrutide's longer half-life means it generates a shallower weekly swing than tirzepatide before any splitting. Net effect: in our calculator's model, a Monday/Thursday split lowers the steady-state peak by about 12% for retatrutide and about 15% for tirzepatide, so the smoothing benefit is somewhat smaller for retatrutide because its starting curve is already flatter.

For the tirzepatide-specific chart with KwikPen and vial considerations, see microdosing tirzepatide chart.

Watch: Split-Dose Mechanics Step by Step

A board-certified physician walks through the practical mechanics of splitting a GLP-1 dose. The mechanics translate directly to retatrutide vials at 10mg/mL.

Frequently Asked Questions

References

1. Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. doi:10.1056/NEJMoa2301972. NEJM
2. Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism. 2022;34(9):1234-1247.e9. doi:10.1016/j.cmet.2022.07.013. PMID: 35985340. PubMed
3. Urva S, Coskun T, Loh MT, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet. 2022;400(10366):1869-1881. doi:10.1016/S0140-6736(22)02033-5. PMID: 36354040. PubMed
4. GLP3Planner.com. Pharmacokinetic Modeling Methodology. methodology. Internal reference for peak-reduction modeling at twice-weekly and three-times-weekly split schedules.
5. ClinicalTrials.gov. A Study of LY3437943 in Participants Who Have Obesity or Overweight (NCT04881760). Posted results, adverse events. ClinicalTrials.gov