Retatrutide: units to draw, the weekly shot and a six-day half-life
Retatrutide is a triple receptor agonist (GLP-1, GIP, glucagon) developed by Eli Lilly and in Phase 3 trials for obesity. The Peppy catalog lists it as a reconstituted vial dosed in mg, weekly, with a half-life of about 144 hours. Peppy converts vial, water and mg into syringe units, keeps the weekly shot day and charts what is still active.
Looking for the medication page? See the GLP-1 tracker for iPhone: every shot, step-up and side effect in one place.
Retatrutide reconstitution calculator
Retatrutide reconstitution calculator
Free in the appHow long Retatrutide stays active
Active in your system — Retatrutide
estimate for weekly doses, half-life 144 hAn estimate from the half-life, not a measurement. Individual clearance varies. Peppy shows this curve for each protocol under Active in your system.
Retatrutide dose steps in the catalog
| Retatrutide — catalog dose ladder | Dose |
|---|---|
| Step 1 | 1 mg |
| Step 2 | 2 mg |
| Step 3 | 4 mg |
| Step 4 | 8 mg |
| Step 5 | 12 mg |
Dose steps as listed in the Peppy catalog so the picker is fast — not a recommendation. Your prescriber sets your dose; Peppy tracks it.
Tracking retatrutide: what matters
Retatrutide has no pen and no label, so the vial math is on you. A retatrutide reconstitution calculator turns the mg on the vial and the water you add into units: 10 mg with 2 mL is 5 mg per mL, so 2 mg is 40 units, 4 mg is 80, and an 8 mg shot would need more than a 1 mL syringe at that concentration. Peppy flags that last case with a warning and lets you try a smaller water volume. It stores the mix on the protocol and prints the units on the card, the reminder and the Log shot sheet. See units to draw.
Doses climb over months in what people track, which changes both the units and the vial life every few weeks. Dose step-ups (Pro) hold each rung with a duration and advance the dose everywhere at once, and the units update with it. Inventory (Pro) counts doses left at the current dose and projects the run-out date. The titration tracker guide shows a multi-month ladder.
Retatrutide is still investigational, so there is no prescribing information to lean on. Peppy states the catalog facts, and the check-in does the rest: nausea, food noise and appetite rated 1 to 5, weight from Apple Health, all tied to the shot you took that week.
Schedule and cycles
The Peppy catalog lists retatrutide as weekly with a dose ladder of 1, 2, 4, 8 and 12 mg (catalog listing, not a recommendation). The Phase 2 trial in NEJM used once-weekly subcutaneous dosing with stepped starting doses, and describes a half-life of approximately 6 days. Peppy's "active in your system" curve uses the catalog's 144 hours as an estimate; it dips a little before each weekly shot and stacks over the first month at each step. Missed and overdue shots are computed from your weekday, never stored. There is no published missed-dose rule; ask your prescriber and see the missed dose guide for what Peppy shows.
How to do this in Peppy
- Open Protocols, tap +, search "retatrutide" (alias LY3437943). The catalog sets vial, mg and weekly.
- Enter your dose. In the inline Calculator, type vial mg and water mL to get units; adjust the water if Peppy warns about the 1 mL limit.
- Pick the weekday and time. Enter your rungs under Dose step-ups (Pro).
- Add vials in Inventory (Pro).
- On shot day, tap the countdown on Today, choose the suggested site on the body map, confirm the units and log.
- Do the daily check-in; Progress (Pro insights) shows weight and side effects against each step.
The retatrutide tracker page covers the weekly routine.
Track it in Peppy
123 compounds built in, the units math done for you, body-map site rotation and reminders — private on your iPhone.
Free · iPhone · no accountFrequently asked
How many units is 2 mg of retatrutide?
Example: a 10 mg vial mixed with 2 mL of bacteriostatic water is 5 mg per mL, so 2 mg is 0.4 mL, or 40 units on a U-100 syringe; 1 mg is 20 units and 4 mg is 80 units. With 1 mL of water every number halves. Enter your vial and water in Peppy's calculator and verify with your prescriber.
How often is retatrutide taken?
The Peppy catalog lists retatrutide as weekly, matching the once-weekly dosing used in the Phase 2 trial. Set the weekday in Peppy and the countdown, reminder (Pro) and widget (Pro) follow it.
What is retatrutide's half-life?
The Peppy catalog lists about 144 hours (6 days). The Phase 2 trial published in the New England Journal of Medicine in 2023 describes a half-life of approximately 6 days, which is what enables weekly administration. Peppy's "active in your system" chart uses the catalog number as an estimate.
Does retatrutide have a dose ladder?
The Peppy catalog lists 1, 2, 4, 8 and 12 mg as the ladder, mirroring the arms studied in the Phase 2 trial. It is a catalog listing, not a recommendation. Dose step-ups (Pro) let you enter whatever rungs your prescriber gave you.
Where do you inject retatrutide?
Most people log subcutaneous sites: abdomen, thighs, upper arms. Peppy's body map suggests the next site and shows when each was last used. See the rotation guide.
How many units is 1 mg of Retatrutide?
It depends on how the vial was mixed. Example: a 10 mg vial plus 2 mL of bacteriostatic water is 5 mg/mL, so 1 mg is 0.2 mL, or 20 units on a U-100 insulin syringe. Change the water and the units change. Use the calculator above with your own vial, and verify with your prescriber.
How long does Retatrutide stay in your system?
The Peppy catalog lists a half-life of about 6 days for Retatrutide. After roughly five half-lives, about 4.3 weeks, most of a single dose has cleared. That is an estimate from the half-life, not a measurement, and individual clearance varies.
Can I track Retatrutide in Peppy?
Yes. Retatrutide is one of 123 compounds built into Peppy, with its form, unit and typical frequency prefilled. Add it as a protocol, set your schedule, and Peppy handles the countdown, the log and the reminders (Pro).
Where should I inject Retatrutide?
Follow your prescriber's instructions. For subcutaneous shots the GLP-1 labels list the abdomen, thigh and upper arm and say to rotate. Peppy's body map has 13 sites, suggests the next one, and shows when each was last used. Read the site rotation guide.
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Not medical advice. Peppy is a tracking tool, not medical advice. Dose calculations are mathematical conversions only. Always follow your prescriber's instructions and verify every draw-up yourself.