Retatrutide Reconstitution Math — 5mg and 10mg Vial Calculations for the Jastreboff Phase 2 Dose Schedule
Retatrutide's phase 2 dose schedule from Jastreboff 2023 NEJM is unusually clean — four titration steps, weekly subcutaneous, three maintenance arms. Translating that into actual U-100 insulin syringe units depends on whether you reconstitute the 5 mg or 10 mg vial with 1, 2, 3, or 5 mL of bacteriostatic water. This is the complete reconstitution math, every titration step, both vial sizes, with the unit math worked out.
1. The Jastreboff 2023 dose schedule — the reference
Jastreboff et al. 2023 in the New England Journal of Medicine reported the phase 2 trial of retatrutide for obesity. The titration schedule, which has become the de-facto research reference:
| Week | Weekly dose | Schedule |
|---|---|---|
| 1-4 | 2 mg | Starting titration |
| 5-8 | 4 mg | Second titration |
| 9-12 | 8 mg | Third titration |
| 13+ | 12 mg | Maintenance (top arm) |
The trial also ran 4 mg and 8 mg maintenance arms. Mean weight reduction at 48 weeks: 8.7% (1 mg arm), 17.1% (4 mg), 22.8% (8 mg), 24.2% (12 mg). The dose-response is roughly linear up to 8 mg and flattens between 8 and 12 mg — most research protocols target the 8 mg maintenance dose as the cost-efficient sweet spot.
2. Choosing your vial — 5 mg or 10 mg
REVIVE LAB UAE stocks both. The decision logic:
| Vial size | Best for | Weeks per vial (8 mg maintenance) | Cost per mg |
|---|---|---|---|
| 5 mg | Titration phase (weeks 1-8 at 2-4 mg) | ~2.5 weeks at 2 mg; ~1.25 weeks at 4 mg | Higher per mg |
| 10 mg | Maintenance phase (8-12 mg/week) | ~1.25 weeks at 8 mg; ~0.83 weeks at 12 mg | Lower per mg |
Practical full-protocol math: a 12-week titration (4 weeks × 2 mg + 4 weeks × 4 mg + 4 weeks × 8 mg) = 56 mg total. That's eleven 5 mg vials or six 10 mg vials. Most researchers ordering a full titration sleeve buy 5 mg for the titration phase and switch to 10 mg vials for maintenance.
3. Reconstitution scenarios — 5 mg vial
Three common bacteriostatic water ratios on the 5 mg vial:
| Bac water | Concentration | 2 mg dose | 4 mg dose | 5 mg dose |
|---|---|---|---|---|
| 1 mL | 5 mg/mL | 40 U (0.40 mL) | 80 U (0.80 mL) | 100 U (1.00 mL — full syringe) |
| 2 mL | 2.5 mg/mL | 80 U (0.80 mL) | full syringe (need 2 mL syringe or split inject) | 2.0 mL (need 3 mL syringe) |
| 3 mL | 1.67 mg/mL | 1.2 mL (need 3 mL syringe) | 2.4 mL (need 3 mL syringe) | 3.0 mL (need 3 mL syringe) |
4. Reconstitution scenarios — 10 mg vial
| Bac water | Concentration | 4 mg dose | 8 mg dose | 12 mg dose |
|---|---|---|---|---|
| 1 mL | 10 mg/mL | 40 U (0.40 mL) | 80 U (0.80 mL) | 1.2 mL (need 3 mL syringe) |
| 2 mL | 5 mg/mL | 80 U (0.80 mL) | 1.6 mL (need 3 mL syringe) | 2.4 mL (need 3 mL syringe) |
| 3 mL | 3.33 mg/mL | 1.2 mL | 2.4 mL | 3.6 mL (need 5 mL syringe or split) |
For 8 mg maintenance, 10 mg + 1 mL = 10 mg/mL gives 80 U — a clean single-syringe draw. For 12 mg, even the most concentrated reconstitution requires more than a U-100 insulin syringe's 1 mL capacity — either step up to a 3 mL syringe or split the dose into two injections at different sites.
5. The split-dose decision
At 12 mg weekly, the injection volume exceeds the standard 1 mL U-100 insulin syringe regardless of reconstitution concentration unless you use the highest possible concentration (10 mg/mL with the 10 mg vial in 1 mL). Two options:
- Single injection, 3 mL syringe. Draw 1.2 mL of 10 mg/mL solution into a 3 mL syringe with 23-25G needle. Inject SC abdominal or thigh.
- Two injections, U-100 insulin syringes. Draw 60 U each, inject at two sites (e.g., left and right lower abdomen).
Most protocols favour single injection with the larger syringe for compliance — two-injection split-dose protocols have higher administration friction.
6. Bac water vs sterile water
Bacteriostatic water (0.9% benzyl alcohol preservative) is the standard reconstitution solvent for multi-dose protocols. Sterile water is only suitable for single-use vials drawn immediately. Retatrutide reconstituted in bac water and refrigerated at 2-8 °C is stable for 28-30 days — enough for one full vial of weekly dosing. Full bac water vs sterile comparison sits in our peptide reconstitution guide.
7. Storage during the dose week
Reconstituted retatrutide should live in the refrigerator at 2-8 °C between weekly injections. UAE summer ambient (45 °C+ peaks in July-August) destroys peptide stability rapidly — never leave a reconstituted vial out at room temperature for more than 2-3 hours total cumulative time. If using insulated pouch for transport, include cold-pack and keep the vial pressed against the cold-pack throughout transit.
8. Injection site rotation
Weekly subcutaneous over 12+ weeks of titration + maintenance means 12-50+ injections at the same body region if not rotated. Standard SC peptide rotation:
- Lower abdomen left → lower abdomen right → upper outer thigh left → upper outer thigh right (4-week cycle)
- Avoid sites with scar tissue, stretch marks, or recent bruising
- Pinch skin, angle 45° (lean tissue) or 90° (more subcutaneous fat) for 5/16-inch needle
9. UAE supply context
Retatrutide is REVIVE LAB UAE's highest-volume SKU. Both 5 mg and 10 mg vials are stocked. Lot-level HPLC certificate of analysis confirms peptide identity and purity ≥98% on every batch. The full Jastreboff-anchored research overview sits in our retatrutide dosing protocol writeup.
Retatrutide UAE ships same-day Dubai on orders before 3 PM, 24 hours nationwide, cold-pack insulation year-round.
10. The summary
- Jastreboff phase 2 titration: 2 → 4 → 8 → 12 mg/week. 8 mg maintenance is the cost-effective sweet spot.
- 5 mg vial + 1 mL bac water = 5 mg/mL → clean U-100 syringe doses for the titration phase.
- 10 mg vial + 1 mL = 10 mg/mL → 80 U for 8 mg maintenance.
- 12 mg dose exceeds U-100 syringe capacity at all concentrations; use 3 mL syringe or split-dose.
- Refrigerated reconstituted vials are stable for 28-30 days; UAE summer demands strict cold-chain.
- REVIVE LAB UAE stocks HPLC-verified retatrutide in 5 mg and 10 mg vials.
References
- 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. PubMed
- Rosenstock J, Frias J, Jastreboff AM, et al. Retatrutide in phase 2 type 2 diabetes — Glycaemic and weight outcomes. Lancet. 2023;402(10401):529-544. PubMed
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple GIP/GLP-1/glucagon receptor agonist. Cell Metab. 2022;34(9):1234-1247. PubMed
- Sanyal AJ, Kaplan LM, Frias JP, et al. Triple hormone receptor agonist retatrutide for MASLD — Subgroup analysis. Nat Med. 2024;30:2037-2048. PubMed
- Reagan-Shaw S, Nihal M, Ahmad N. Dose translation from animal to human studies revisited. FASEB J. 2008;22(3):659-661. PubMed