Retatrutide is the first triple agonist targeting GLP-1, GIP, and glucagon receptors simultaneously. Phase 2 data showed up to 24.2% body weight reduction at 48 weeks — the greatest pharmacological weight loss ever recorded in a clinical trial.
This peptide profile is for research and educational purposes only. Not intended for human use or self-administration.
Overview
Retatrutide (LY3437943) was developed by Eli Lilly as the next evolution beyond dual incretins like tirzepatide. By adding glucagon receptor agonism to the GLP-1 and GIP activity, retatrutide creates a three-pronged metabolic intervention: appetite suppression and improved insulin secretion (GLP-1), enhanced fat metabolism and insulin sensitivity (GIP), and increased energy expenditure (glucagon). The addition of glucagon activity is particularly significant — glucagon drives thermogenesis and fat oxidation in the liver and adipose tissue, which is not achieved by GLP-1/GIP combinations alone. Phase 2 results published in NEJM (2023) were unprecedented in obesity pharmacology.
Mechanism of Action
Retatrutide activates three receptors. GLP-1 receptor: slows gastric emptying, reduces appetite, stimulates glucose-dependent insulin secretion, and suppresses glucagon post-meal. GIP receptor: enhances insulin secretion, promotes adipose lipid uptake and oxidation, and may reduce GI side effects of the GLP-1 component. Glucagon receptor: increases hepatic glucose production (offset by GLP-1 and GIP effects), drives thermogenesis through brown adipose tissue activation, stimulates lipolysis, and increases energy expenditure by 10–15% above baseline. The net effect of triple agonism is greater caloric deficit, higher fat oxidation, and enhanced metabolic rate — all without requiring physical activity changes.
Key Research
Phase 2 NEJM trial (N=338, 48 weeks): retatrutide produced 17.5% weight reduction at 4 mg and 24.2% at 12 mg — the latter representing more weight loss than most bariatric procedures at 1 year. 100% of participants at the highest dose achieved ≥5% weight loss; 83% achieved ≥15%. Liver fat content was reduced by 80% from baseline — significant for NASH/MAFLD treatment potential. Phase 3 trials (TRIUMPH) were initiated in 2023. Cardiovascular outcomes data is not yet available. Safety profile was consistent with the GLP-1 class with additional glucagon-mediated effects.
Retatrutide is escalated very slowly due to the combined GI burden of triple receptor agonism: starting at 0.5 mg weekly and titrating up over 20+ weeks to a target dose. Phase 3 trials use a structured escalation protocol. This is a Phase 3 investigational compound — it is not approved or commercially available as of 2024. Research access is through clinical trials only. Any protocol should follow the study's titration guidelines.
Phase 3 Research Protocol: follow clinical trial titration schedule (0.5 mg → 12 mg over ~20 weeks). Not available outside clinical trial contexts as of 2024. Future: likely to be combined with amylin analogs (cagrilintide) or GLP-2 agents once approved, for maximum metabolic coverage.
Reported Side Effects
Side effects summarized from animal studies and researcher community observations. Educational purposes only — not medical advice.
GI side effects (nausea, vomiting, diarrhea) are more frequent than with GLP-1 or GLP-1/GIP dual agonists due to triple receptor activity — slower dose titration is required. Heart rate elevation (from glucagon receptor activity) is a notable distinction from tirzepatide — mean increases of 2–5 bpm have been observed. Gallbladder effects and potential thyroid concerns carry the same class considerations as GLP-1 agents. The glucagon component increases the risk of mild transient hyperglycemia during dose escalation in subjects without diabetes. Injection site reactions are mild.
Storage & Handling
Investigational compound — storage per clinical trial protocol and manufacturer guidance. Typically stored at 2–8°C, protected from light, in pre-filled injection devices. Same general handling principles as tirzepatide apply.
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