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.
What we do not know
- It is not approved anywhere. Phase 3 is ongoing, so there is no regulator-reviewed label, no approved dosing, and no long-term safety dataset.
- Published human data is Phase 2, at 48 weeks. Nothing longer exists.
- The glucagon arm raises heart rate more than GLP-1 alone in trials; whether that matters over years is unknown.
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.
How it is thought to work
A triple agonist at the GLP-1, GIP and glucagon receptors. The glucagon arm is the difference from tirzepatide: glucagon receptor activity raises energy expenditure and acts on hepatic fat, in principle adding to the appetite suppression the other two provide.
What the evidence supports
This table grades how well each outcome has been studied in humans, not how well Retatrutide works. A strong grade means the question was asked properly, and the answer may still have been negative. Nothing here is inherited from a drug class, a close analog, or the parent molecule of a fragment.
| Outcome | Strongest published evidence |
|---|---|
| Glycemic control | Human RCT |
| Hepatic steatosis / MASLD | Human RCT |
| Weight loss | Human RCT |
| Long-term safety | No data |
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 2023PMID 37366315 · DOI
- Sanyal et al., Retatrutide for MASLD, Nature Medicine 2024