Retatrutide Pen
3 mL of LY3437943, a lipidated GIP, GLP-1 and glucagon receptor agonist, in bacteriostatic water at 5 mg/mL, 15 mg per pen. Filled from a peptide lot tested in the manufacturer’s own laboratory, with a certificate.
| Compound | Retatrutide LY3437943; GIP/GLP-1/glucagon receptor triple agonist |
|---|---|
| CAS number | 2381089-83-2 |
| Molecular formula | C221H342N46O68 |
| Theoretical mass | 4731.4 Da |
| Sequence / structure | H-Y-Aib-QGTFTSDYSI-[αMeLeu]-LDKK(AEEA-γGlu-C20 diacid)AQ-Aib-AFIEYLLEGGPSSGAPPPS-NH₂ (39 residues; Aib2, α-methyl-Leu13, Aib20; Lys17 acylated with eicosanedioic acid via γ-Glu and AEEA; C-terminal amide) |
| Contents | Retatrutide: 15 mg per 3 mL pen (0.5% w/v) |
| Form | Sterile aqueous solution in bacteriostatic water (0.9% benzyl alcohol), supplied in a 3 mL glass cartridge inside a preloaded autoinjector pen fitted with a needle |
| Storage, sealed | Store at 2–8 °C in the original carton, protected from light |
| Format | Solution in a 3 mL pre-filled pen |
Sizes and lots
- 15 mg · 1 pen — $98.99
- 15 mg · Kit of 10 — $880.02
Retatrutide (LY3437943) is an investigational peptide agonist of the GIP, GLP-1 and glucagon receptors, with a 20-carbon diacid side chain on lysine 17. This listing is a preloaded pen holding a 3 mL glass cartridge of ready-made solution at 5 mg/mL, 15 mg of peptide in all, so there is no powder to reconstitute. Research on retatrutide runs from receptor pharmacology and mouse work to phase 2 and phase 3 clinical trials.
What is in the pen
The cartridge holds 3 mL of sterile aqueous solution. Retatrutide is present at 0.5% w/v, which is 5 mg/mL and 15 mg per pen; at the certificate's theoretical mass of 4731.4 Da that works out to about 1.06 mM, or roughly 3.2 µmol in the whole pen. The solvent is bacteriostatic water with 0.9% benzyl alcohol as an antimicrobial preservative. On the safety data sheet, benzyl alcohol carries hazard statements for harm if swallowed or inhaled, serious eye irritation and allergic skin reactions, and retatrutide itself is classified Repr. 2 (H361), suspected of damaging fertility or the unborn child.
Keep the pen at 2 to 8 °C in its original carton, away from light, capped once in use and stored locked up. It must not be frozen, and a pen whose solution has frozen, discoloured or turned cloudy should be discarded. The same peptide is sold freeze-dried in the retatrutide 10 mg vial and the other fills, and peptide pen vs vial sets out the general differences between the two formats.
What the research covers
Coskun and colleagues introduced LY3437943 in 2022 as a triple agonist whose in vitro activity at the glucagon and GLP-1 receptors was balanced, with stronger activity at the GIP receptor1. In obese mice they found that energy expenditure driven through the glucagon receptor added to the reduced calorie intake attributed to the two incretin receptors1.
Human evidence comes from trials of an investigational drug run under medical supervision. The phase 2 obesity trial randomised 338 adults to retatrutide or placebo, with percentage change in body weight at 24 weeks as the primary end point and follow-up to 48 weeks2. How much each receptor contributes in people has not been worked out; the receptor-level evidence comes from cell and mouse experiments1. Phase 3 trials in type 2 diabetes, non-alcoholic fatty liver disease and obesity were started in August 2023, according to a 2024 review3.
None of these papers examined retatrutide held in solution, and none tested a preloaded pen or research-grade material, so the storage limits on the safety data sheet are the ones that apply to this format. The full literature, including the liver fat substudy, the diabetes trials and the 2026 phase 3 announcements, is in the retatrutide vs tirzepatide guide.
Frequently asked questions
How does the pen differ from the retatrutide vials?
The vials hold freeze-dried powder, stored at −20 °C and dissolved in the lab at whatever volume the work calls for. The pen holds 15 mg already dissolved at a fixed 5 mg/mL in bacteriostatic water, and it is refrigerated at 2 to 8 °C, never frozen.
Is there published stability data for retatrutide in solution?
Not in the references on this page. The discovery and trial papers describe the molecule and its effects rather than how long it lasts in bacteriostatic water, so follow the storage conditions and discard criteria on the safety data sheet.
References
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.e9. DOI · PubMed
- 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. DOI · PubMed
- Kaur M, Misra S. A review of an investigational drug retatrutide, a novel triple agonist agent for the treatment of obesity. Eur J Clin Pharmacol. 2024;80(5):669-676. DOI · PubMed
For laboratory research use only. Not for human or veterinary consumption. Products have not been evaluated by the U.S. Food and Drug Administration and are not intended to diagnose, treat, cure or prevent any disease.