What Retatrutide is
Retatrutide is an investigational triple agonist (GLP-1, GIP, and glucagon receptors) from Eli Lilly, currently in Phase 3 trials and not FDA approved. Its Phase 2 results showed the largest average weight reduction reported for any incretin drug to date, which is why it dominates gray-market interest.
Because it is unapproved, there is no label to follow: the schedule below is the Phase 2 dose-escalation protocol, and everything else about real-world use (vial sizes, concentrations) is vendor convention, not a standard.
Reconstitution math
Concentration is everything: the same 10 mg vial gives a different draw for every amount of bacteriostatic water you add. The table uses the common 2 mL setup for each vial size, which puts every unit on a U-100 insulin syringe at 50 mcg for the default vial. Dashes mark draws too small to measure or larger than the syringe.
| Vial | BAC water | Concentration | 2 mg | 4 mg | 6 mg | 8 mg | 12 mg |
|---|---|---|---|---|---|---|---|
| 5 mg | 2 mL | 2.5 mg/mL | 80 u | - | - | - | - |
| 10 mg | 2 mL | 5 mg/mL | 40 u | 80 u | - | - | - |
| 15 mg | 2 mL | 7.5 mg/mL | 26.7 u | 53.3 u | 80 u | - | - |
| 30 mg | 2 mL | 15 mg/mL | 13.3 u | 26.7 u | 40 u | 53.3 u | 80 u |
Dosing and protocol
Phase 2 TRIUMPH escalation: 2 to 12 mg weekly; some arms held at 8 mg.
The trials escalated every four weeks from 2 mg toward 8 or 12 mg weekly. Tolerability, not effect, sets the pace; some Phase 2 arms deliberately stopped at 8 mg. The half-life of about six days means steady state arrives around week four to five at any given step.
Pharmacokinetics
Retatrutide has published human pharmacokinetics: dose-proportional kinetics across the 0.5 to 12 mg range. The curves below are normalized one-compartment models built from the cited half-life, the same math the Planner uses. They show shape and timing, not absolute blood levels.
Storage and handling
Lyophilized vials keep best cold, dark, and dry; refrigeration is the community default and freezing lyophilized powder is common for long holds. After reconstitution, refrigerate at 2 to 8 C, do not freeze the solution, and date the vial. Bacteriostatic water's preservative keeps multi-dose use practical for about 28 days by USP convention, though our 120-day stability study found the preservative itself outlasts that window.
As an investigational compound there is no official storage guidance for vials. The community default mirrors the approved incretins: refrigerate after reconstitution, protect from light, and do not freeze the solution. Our lab-tested stability data for retatrutide is linked below when published.
Got a certificate of analysis with your vial? Run it through our COA Reader: it reads the report in plain English, checks purity and mass against the label claim, and links the testing lab’s own verification page. Our guide to reading a COA explains what the numbers do and do not tell you.
Sources
- Jastreboff et al., Triple-hormone-receptor agonist retatrutide for obesity, NEJM 2023
- Sanyal et al., Retatrutide for MASLD, Nature Medicine 2024