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WEIGHT LOSS

Retatrutide

Retatrutide (LY3437943)

Triple Agonist Peptide for Weight Loss

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— authoritative voices whose published research informed this article

The information on this page is compiled from peer-reviewed research and is provided for educational and research purposes only. It is not medical advice, a diagnosis, or a treatment recommendation. Peptides discussed here may not be approved for human use in your jurisdiction. Always consult a qualified healthcare provider before starting, stopping, or modifying any health protocol.

Overview

What is Retatrutide?

Retatrutide (LY3437943) is an investigational triple hormone receptor agonist developed by Eli Lilly. Unlike GLP-1 monotherapy agents such as semaglutide, retatrutide simultaneously targets three key metabolic receptors: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and the glucagon receptor.

While semaglutide targets GLP-1 alone and tirzepatide targets GLP-1 plus GIP, the addition of glucagon receptor agonism in retatrutide creates a more powerful metabolic effect. Glucagon receptor activation increases energy expenditure and promotes fat burning in the liver, working synergistically with the appetite suppression of GLP-1 and the insulin sensitization of GIP.

In Phase 2 clinical trials (TRYBE-1), retatrutide demonstrated unprecedented weight loss results. Participants receiving the highest dose (12 mg weekly) achieved an average body weight reduction of approximately 24% over 48 weeks. This surpasses outcomes seen with semaglutide (approximately 15%) and tirzepatide (approximately 21%) in comparable trial populations.

Retatrutide is currently in Phase 3 clinical trials. It is not FDA-approved and remains an investigational compound. All research-use information on this page is derived from peer-reviewed clinical trial publications and pre-clinical data.

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Protocol

Dosage Guide

Route: Subcutaneous injection, once weekly

Dosing Schedule

PeriodDose
Weeks 1-42 mg
Weeks 5-84 mg
Weeks 9-128 mg
Week 13+12 mg (highest studied dose)

Reconstitution

VIAL SIZE10 mg
WATER VOLUME2 mL
CONCENTRATION5 mg/mL
Each 0.1 mL (10 units on a U-100 insulin syringe) = 0.5 mg

Injection Volumes

DoseVolumeSyringe Units
2 mg0.4 mL40 units
4 mg0.8 mL80 units
8 mg1.6 mLUse two injections of 0.8 mL
12 mg2.4 mLUse two injections of 1.2 mL

Administration Tips

  • Inject subcutaneously in the abdomen, thigh, or upper arm
  • Rotate injection sites weekly to avoid lipohypertrophy
  • Administer on the same day each week for consistent plasma levels
  • Store reconstituted solution refrigerated (2-8C) and use within 28 days
  • Allow solution to reach room temperature before injecting to reduce discomfort
  • Use a 29-31 gauge, 4-8mm pen needle or insulin syringe
Safety

Risks & Side Effects

Commonly Reported

NauseaDiarrheaVomitingConstipationDecreased appetiteAbdominal painDyspepsiaInjection site reactionsFatigue

Serious Risks

Pancreatitis

Risk of pancreatic inflammation, as with other incretin-based therapies. Discontinue immediately if severe abdominal pain develops.

Gallbladder disease

Rapid weight loss may increase the risk of gallstone formation. Biliary colic and cholecystitis have been reported with GLP-1 class agents.

Hypoglycemia

Particularly when combined with other glucose-lowering agents such as sulfonylureas or insulin. Monitor blood glucose carefully.

Hepatotoxicity

Glucagon receptor activation may affect liver function; monitoring of liver enzymes is recommended during use.

Increased heart rate

Dose-dependent increases in resting heart rate were observed in Phase 2 trials at higher doses, consistent with other GLP-1 receptor agonists.

Thyroid C-cell tumors

A theoretical risk based on GLP-1 receptor agonist class warnings from rodent studies. Clinical significance in humans remains under investigation.

Related Research

Related Peptides

Expert Voices

Experts Covering Retatrutide

Dr. William A. Seeds

MD -- Regenerative Medicine Pioneer

Dr. Andrew Huberman

PhD -- Stanford Neuroscientist

Jay Campbell

Health Optimization Author and Peptide Advocate

Dr. Ian W. Hamley

Diamond Professor of Physical Chemistry -- University of Reading

Dr. Daniel J. Drucker

MD, FRCPC, FRSC -- GLP-1 Discovery Pioneer

LEGAL DISCLAIMER

The information provided on this page is for educational and informational purposes only and is not intended as medical advice. Retatrutide is an investigational compound that has not been approved by the FDA or any regulatory authority. Always consult with a qualified healthcare professional before starting any peptide therapy. Individual results may vary. Peptides Institute is not responsible for any adverse effects resulting from the use of information provided on this site.

Frequently Asked Questions

What is retatrutide?
Retatrutide (LY3437943) is an investigational triple hormone receptor agonist developed by Eli Lilly. It simultaneously targets GLP-1, GIP, and glucagon receptors. Phase 2 trials showed average body weight reductions of approximately 24% over 48 weeks, surpassing results seen with semaglutide or tirzepatide. It is not FDA-approved.
How does retatrutide work?
Retatrutide activates three metabolic receptors at once. GLP-1 agonism suppresses appetite; GIP agonism improves insulin sensitivity; glucagon receptor agonism increases energy expenditure and fat burning in the liver. The combined effect produces greater weight loss than single- or dual-receptor approaches observed in comparable clinical populations.
How does retatrutide compare to semaglutide and tirzepatide?
In Phase 2 data, retatrutide produced roughly 24% body weight reduction versus approximately 15% for semaglutide and 21% for tirzepatide. The additional glucagon receptor agonism sets retatrutide apart. Direct head-to-head trials have not been completed, so comparisons are cross-trial estimates from different study populations.
What are the side effects of retatrutide?
The most common side effects are gastrointestinal: nausea, diarrhea, vomiting, constipation, and abdominal pain. More serious risks include pancreatitis, gallbladder disease, elevated heart rate, hepatotoxicity related to glucagon receptor activation, and a theoretical thyroid C-cell tumor risk shared with GLP-1 class agents.
What is the retatrutide dosage used in clinical trials?
The TRYBE-1 Phase 2 trial used a gradual escalation: 2 mg for weeks 1-4, 4 mg for weeks 5-8, 8 mg for weeks 9-12, then up to 12 mg weekly thereafter. This titration schedule is designed to minimize gastrointestinal side effects while advancing to the highest studied dose.
Is retatrutide legal to use?
Retatrutide is not FDA-approved and has no approved indication in any country as of the time of writing. It exists only as an investigational compound in ongoing clinical trials. Obtaining or using retatrutide outside a supervised clinical trial is not sanctioned and carries significant regulatory and safety uncertainty.
When will retatrutide be approved?
Retatrutide is currently in Phase 3 clinical trials as of the latest available data. FDA approval, if granted, would typically follow successful Phase 3 completion and regulatory review, a process that generally takes several years. No official approval timeline has been announced by Eli Lilly.

References

  1. Jastreboff AM, Kaplan LM, Frias JP, et al.. Triple-Hormone-Receptor Agonist Retatrutide for Obesity -- A Phase 2 Trial. N Engl J Med. 2023. PMID 37366315
  2. Rosenstock J, Frias JP, Jastreboff AM, 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 conducted in the USA. Lancet. 2023. PMID 37385280
  3. Sanyal AJ, Bedossa P, Engel SS, et al.. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nat Med. 2024. PMID 38858523

Regulatory & Official Sources