Quick answer: Retatrutide has no FDA-approved label and no approved schedule; its Phase 2 trial and every registered trial that states a schedule give it once a week. Split twice a week, a 2 mg weekly dose is 1 mg per injection (15 units at 6.67 mg/mL). In the model (approximate: the time to peak is a model assumption) the weekly total and the total exposure stay the same, the peak is about 12% lower and the trough about 21% higher than one weekly injection.
Can you take reta twice a week?
Retatrutide is investigational. It has no FDA-approved label, so there is no approved schedule to follow or to depart from. Its Phase 2 trial gave it once weekly (Jastreboff et al., N Engl J Med 2023). No trial registered on ClinicalTrials.gov describes a split or more-than-weekly schedule: of 35 records checked on 23 October 2026, the 14 that state a retatrutide schedule give it once weekly and 21 state none. This page shows what the model says a split would do to drug levels; it is not a recommendation to split.
What splitting changes, and what it does not
Splitting divides the same weekly dose into smaller injections. The weekly total does not change, and in the model neither does the total exposure over the week (the area under the curve): a 2 mg week is a 2 mg week however you divide it. What changes is the shape. With a half-life of about 6 days, a smaller dose every few days keeps the level from climbing as high after each injection or sagging as low before the next one.
In the model, Monday and Thursday puts the steady-state peak about 12% lower and the trough about 21% higher than one weekly injection, moving the peak-to-trough ratio from 1.84 to 1.35. Daily injections flatten it to 1.03. With evenly spaced injections, each extra injection a week buys less smoothing than the one before; with uneven days it depends on which day you add.
Why the days you pick matter
Only the gaps between injections matter, not the weekday names: Sunday and Wednesday behaves like Monday and Thursday. Uneven gaps let the level sag further over the longest one, so Monday and Thursday (a 3-day and a 4-day gap) gives about 1.35, while an even split every 3.5 days, such as Monday morning and Thursday evening, gives about 1.27. Two injections close together and a long gap after them, such as Monday and Tuesday, smooth the curve much less. Tap different days in the calculator to see it.
What this tool does not tell you
It does not tell you whether to split your dose. It models population-average drug levels, not your blood levels, and it says nothing about side effects or how well the medication works: a lower modelled peak is not evidence that nausea or weight loss changes. Smaller injections also mean smaller draws, so check every draw against your own vial. The "Doses in One Vial" figure counts by volume only: FDA generally recommends using multi-dose vials of sterile medications within 28 days of first use, and this tool does not tell you how long an opened vial stays usable. For Retatrutide the time to peak is the calculator's own assumption, so its figures are approximate. The trough figures depend mainly on the half-life; the peak and the peak-to-trough ratio also depend on the assumed time to peak (1 to 2 days moves the Monday and Thursday ratio between about 1.28 and 1.42).
Frequently asked questions
Can you take reta twice a week?
Retatrutide is investigational and has no FDA-approved label, so there is no approved schedule of any kind. Its Phase 2 trial gave it once weekly, and no trial registered on ClinicalTrials.gov describes a split or more-than-weekly schedule (35 records checked 23 October 2026). This tool does not tell you whether to split. In the model, a Monday and Thursday split of the same weekly dose puts the steady-state peak about 12% lower and the trough about 21% higher than one weekly injection: a peak-to-trough ratio of about 1.35 instead of about 1.84. These figures are approximate for Retatrutide: the time to peak is a model assumption.
How much reta is each injection if I split my dose?
Divide the weekly dose by the number of injections. 2 mg a week as two injections is 1 mg each; with a 20 mg vial mixed with 3 mL of water (6.67 mg/mL) that is 15 units (0.15 mL) on a U-100 syringe. The weekly total does not change. Enter your own dose, days and vial above.
Does splitting lower the peak?
In the model, yes. Twice weekly (Monday and Thursday) the peak is about 12% lower and the trough about 21% higher than once weekly; daily injections give a peak about 21% lower and a trough about 43% higher. The total amount over the week (the area under the curve) is the same for every schedule with the same weekly dose: splitting reshapes the curve, it does not add or remove drug. These figures are approximate for Retatrutide: the time to peak is a model assumption.
Is Monday and Thursday the same as every 3.5 days?
Close, but not quite. Monday and Thursday leaves a 3-day gap and a 4-day gap, and the level sags further over the longer one: a peak-to-trough ratio of about 1.35. Injecting every 3.5 days (for example Monday morning and Thursday evening) gives about 1.27. Only the gaps matter, so Sunday and Wednesday is the same as Monday and Thursday. These figures are approximate for Retatrutide: the time to peak is a model assumption.
Does splitting reduce nausea or change how well it works?
This tool cannot tell you. It models drug levels, not effects or side effects, and a lower modelled peak is not evidence that nausea or weight loss changes. Talk to a clinician before changing how you take a medication.
How is this calculated?
A one-compartment model with first-order absorption, the same model as the GLP3 Planner half-life calculator, for the injection. For Retatrutide: half-life about 6 days (Phase 1b trial, Urva 2022, PMID 36354040: approximately 6 days) and time to peak 1.5 days (model assumption: no FDA-approved label), so treat its figures as approximate. The weekly dose is divided evenly over your injection days, every dose's curve is added together until the weekly pattern repeats, and the highest and lowest points of that week are compared with the same total taken once a week. Check: no schedule can swing more than instant absorption allows, 2^(7 / 6) = 2.24 once weekly; the model gives 1.84. The percentages do not depend on your dose or on how much of the dose is absorbed.
Safety: Retatrutide is an investigational compound and is not approved by the FDA. This tool is educational only. It models population-average drug levels, not your own, and it does not recommend a dosing schedule or tell you to split a dose. Talk to your prescriber before changing how you take a medication, and double-check every draw against your own vial.