Retatrutide

Identity

Mechanism of action

Plain language

Retatrutide activates three different gut and pancreas hormone receptors at once, the two that semaglutide and tirzepatide use, plus a third (glucagon) that increases the body's resting energy burn. That third receptor is the reason it is being investigated for larger weight-loss effect sizes than dual or single agonists.

Technical

Retatrutide is a triple agonist at the GIP receptor (GIPR), GLP-1 receptor (GLP-1R), and glucagon receptor (GCGR). In vitro cell-based potency data (EC50) reported in a 2025 review show it is most potent at GIPR (EC50 0.0643 nM), intermediate at GLP-1R (EC50 0.775 nM), and least potent at GCGR (EC50 5.79 nM), weaker than native glucagon at its own receptor but still active enough at typical trial doses to drive the increased energy expenditure associated with glucagon receptor agonism. GCGR activation is the mechanistic differentiator from GLP-1-only and GIP/GLP-1 dual agonists: it increases hepatic glucose output and lipid oxidation, offset by the insulinotropic GIP/GLP-1 effects, but adds a thermogenic, energy-expenditure component not present in semaglutide or tirzepatide.

Sources: PMC review, Retatrutide:, 2025

What it’s used for

Human trials, not approved for this use

• Obesity, without diabetes: phase 2 randomized controlled trial, 48 weeks, doses of 1, 4, 8, and 12 mg weekly (with 2 mg or 4 mg starting/lead-in doses at the higher levels). Placebo-adjusted mean weight reduction of 16% at 24 weeks and 22% at 48 weeks with the 12 mg dose; approximately 85% of 12 mg participants achieved at least 10% weight loss, 45% achieved at least 20%.

  Sources: Jastreboff AM, et, 2023

• Type 2 diabetes: phase 2 randomized controlled trial, 36 weeks, 281 participants randomized to 0.5, 4, 8, or 12 mg retatrutide, dulaglutide 1.5 mg, or placebo. HbA1c below 6.5% achieved in up to 82% of participants; body weight reduction up to 17% at the 8-12 mg doses.

  Sources: Rosenstock J, et, 2023

• Metabolic dysfunction-associated steatotic liver disease (MASLD, liver fat): phase 2a randomized controlled trial.

  Sources: Triple hormone receptor, 2024

• Body composition substudy in type 2 diabetes, examining fat mass versus lean mass changes.

  Sources: Retatrutide body composition, 2025

Off-label / community use

• Retatrutide is sold exclusively through research-chemical and compounding channels in the absence of any approval; every use in a human being outside a registered clinical trial is by definition off-label and unsupervised, with no controlled human dosing data outside the phase 2 trials. Community dosing practice is anecdotal and directly extrapolated from the trial doses without the trial's medical supervision, lab monitoring, or controlled titration criteria.

  Sources: Jastreboff AM, et, 2023

Pharmacokinetics

Reconstitution

Worked example

There is no FDA-approved retatrutide product, so there is no pen or prefilled-syringe form; everything sold as retatrutide is a research-chemical or compounded product, typically lyophilized powder in a vial, reconstituted by the buyer, and every figure here is a commercial vendor claim, not clinical guidance. Using a commonly advertised 20 mg vial reconstituted with 2 mL of bacteriostatic water: concentration = 20 mg / 2 mL = 10 mg/mL. At this concentration, 1 U-100 syringe unit (0.01 mL) = 0.1 mg. Converting the phase 2 trial dose levels to units: 1 mg = 10 units; 2 mg (lead-in) = 20 units; 4 mg = 40 units; 8 mg = 80 units; 12 mg = 120 units, which exceeds a standard 100-unit (1 mL) U-100 insulin syringe. As with tirzepatide's top dose, the 12 mg trial dose cannot be drawn into a single standard 1 mL syringe at this concentration; a higher-concentration reconstitution or a larger syringe would be required, and vendor pages that gloss over this are describing an impractical or unsafe draw.

Sources: Bolt Pharmacy UK,, Great Northern Peptides,, Glunovabio retatrutide mixing

Storage and post-reconstitution stability

Unopened storage

No FDA-approved product exists. Lyophilized research/compounded vials are stored per vendor instructions, generally refrigerated before reconstitution; see reconstitution and post_reconstitution_stability for the only sourced handling data.

Post-reconstitution stability – Vendor claim

28-30 days refrigerated when bacteriostatic water is used; vendors claim non-bacteriostatic (sterile, preservative-free) water reconstitutions should be used within 24-48 hours. 2-8C, refrigerated

Sources: GLP3 Planner retatrutide

No citable figure. These are commercial vendor claims with no regulatory validation; no FDA or equivalent regulatory stability data exists because no approved retatrutide product exists.

Safety

Notable risks

• No FDA boxed warning exists because there is no approved label. Retatrutide shares the mechanistic GLP-1/GIP-agonist class concern for thyroid C-cell tumors seen in rodent studies of semaglutide, tirzepatide, and liraglutide; whether this rodent finding applies to retatrutide specifically has not been addressed by a citable source, and this gap is stated rather than filled. No contraindication language for retatrutide could be sourced because no approved label exists to state one.

  Sources: PMC review, Retatrutide:, 2025

• Gastrointestinal adverse events (nausea, diarrhea, vomiting, constipation) were the most common trial-reported adverse effects, were dose-related, were mostly mild to moderate, and were partially mitigated by a lower (2 mg vs. 4 mg) starting dose. Dose-dependent increases in heart rate were observed, peaking around 24 weeks and declining thereafter.

  Sources: Jastreboff AM, et, 2023

• A separate review reported gastrointestinal-driven trial discontinuation rates in the range of 20-50% within the first year across dose groups, and noted less frequent elevated ALT and skin hyperesthesia.

  Sources: PMC review, Retatrutide:, 2025

• No FDA-mandated monitoring exists because there is no approved label. Trial protocols included standard gastrointestinal adverse-event tracking, heart-rate monitoring, and liver enzyme checks; anyone using retatrutide outside a supervised trial has no equivalent structured monitoring, which is itself a safety gap worth stating plainly rather than glossing over.

  Sources: Jastreboff AM, et, 2023

Sources

1. Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. doi:10.1056/NEJMoa2301972 (2023)
2. Rosenstock J, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial. Lancet. 2023;402(10401):529-544. doi:10.1016/S0140-6736(23)01053-X (2023)
3. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature Medicine. 2024 (2024)
4. Retatrutide body composition substudy in type 2 diabetes, Lancet Diabetes & Endocrinology 2025 (2025)
5. PMC review, Retatrutide: A Game Changer in Obesity Pharmacotherapy (2025)
6. Bolt Pharmacy UK, retatrutide bacteriostatic-water reconstitution guide (commercial)
7. Great Northern Peptides, retatrutide dosing guide for researchers (commercial)
8. Glunovabio retatrutide mixing guide (commercial)
9. GLP3 Planner retatrutide reconstitution guide (commercial)
10. Chemical-vendor and database sources for retatrutide molecular data (MedChemExpress data sheet; also ChemicalBook and KEGG DRUG D12430)
11. peptidedosages.com, Retatrutide 10 mg vial dosage protocol