Triple GLP-1/GIP/Glucagon Agonist — LY3437943
A triple agonist targeting GLP-1, GIP, and glucagon receptors simultaneously — the next frontier beyond tirzepatide's dual mechanism. Developed by Eli Lilly, retatrutide showed 24.2% average weight loss in Phase 2 trials — the highest ever recorded for a pharmacological intervention at the time. Phase 3 trials are ongoing. Currently available only as a research compound, with significant quality concerns in the unregulated market.
01 — Research Summary
Retatrutide's evidence base is at an earlier stage than tirzepatide or semaglutide — but the Phase 2 data is genuinely remarkable, producing weight loss numbers that exceeded everything previously documented. The caution is that Phase 2 and Phase 3 results don't always align.
24.2% average weight loss at 48 weeks. The Phase 2 trial published in the New England Journal of Medicine showed retatrutide 12mg produced 24.2% average weight loss at 48 weeks — the highest ever recorded for a pharmacological intervention at that time, exceeding tirzepatide's Phase 2 results.
Glucagon component drives additional energy expenditure. Research clarified that the glucagon receptor component drives hepatic glucose production suppression and increased energy expenditure — adding a third mechanism beyond insulin regulation and appetite suppression that may explain the superior weight loss vs. dual agonists.
Phase 3 trials initiated across multiple indications. Eli Lilly initiated the TRIUMPH Phase 3 programme covering obesity, type 2 diabetes, NASH/MASH, and cardiovascular outcomes. Results expected 2025–2026, with potential FDA submission to follow.
Significant liver fat reduction alongside weight loss. Phase 2 data showed meaningful reductions in liver fat alongside the weight loss, suggesting potential application in NASH/MASH — a large unmet medical need where pharmacological options are limited.
02 — Mechanism of Action
Retatrutide adds a third receptor target — glucagon — to the dual GIP/GLP-1 mechanism of tirzepatide. The glucagon component is the key differentiator and the likely explanation for the incremental weight loss benefit.
Retatrutide activates GLP-1, GIP, and glucagon receptors simultaneously from a single molecule. The technical challenge of balancing three receptor agonisms — where too much glucagon activity would worsen glucose control — required significant molecular engineering. The fatty acid modification enables weekly dosing.
The GLP-1 and GIP components work identically to tirzepatide — insulin secretion, glucagon suppression, central appetite reduction, and gastric slowing. These two mechanisms alone would be expected to produce tirzepatide-like weight loss.
The glucagon receptor component adds a third dimension: increased hepatic glucose production (which sounds counterintuitive) is offset by the GLP-1/GIP glucose suppression, while the net effect is increased basal metabolic rate and enhanced fat oxidation — driving additional caloric expenditure beyond appetite suppression.
Glucagon receptor agonism drives hepatic fatty acid oxidation and reduces liver fat accumulation — explaining the NASH/MASH signal in Phase 2 and distinguishing retatrutide's metabolic effects from pure GLP-1 mechanisms.
Retatrutide is still in Phase 3 trials and not FDA-approved. Research-grade retatrutide sold outside clinical trials has significant quality concerns — the compound is technically complex to synthesise correctly, and there is essentially no independent verification of most market product. If considering research use, COA verification is more important here than for any other compound on this site.
03 — Dosing Protocols
No approved dosing protocol exists. The following reflects Phase 2 trial protocols only — real-world research use mirrors this but with the important caveat that product quality is highly variable.
| Protocol | Dose | Frequency | Duration | Notes |
|---|---|---|---|---|
| Phase 2 protocol — low | 1–4 mg/week | Weekly escalation | 24 weeks | Phase 2 starting range. Significant GI side effects at this stage. |
| Phase 2 protocol — mid | 4–8 mg/week | Weekly | Ongoing | Mid-range from trial — meaningful weight loss begins here. |
| Phase 2 protocol — high | 8–12 mg/week | Weekly | Ongoing | Highest doses from Phase 2. 24% average weight loss at 12mg. |
| Research community protocol | 2–8 mg/week | Slow escalation | 12–24 weeks | Community protocols err toward lower doses given quality uncertainty. |
Retatrutide is not FDA-approved. Research-grade product quality is highly variable — this is the compound on this site with the most significant sourcing risk. GI side effects appear more pronounced than tirzepatide at equivalent weight loss doses. Phase 3 data will determine whether Phase 2 results hold at scale.
04 — Community Experiences
Retatrutide has a smaller but intensely interested community — primarily experienced GLP-1 users who have already run semaglutide or tirzepatide and are seeking the next frontier. The Phase 2 NEJM data is frequently cited and the 24% weight loss figure generates significant excitement. The dominant community concerns are sourcing quality and the uncertainty of Phase 3 outcomes.
These are user-reported experiences from public forums. Not endorsed by Whats That Peptide and should not be interpreted as clinical evidence. Individual results vary. Always consult a healthcare professional.
"The Phase 2 results are extraordinary but Phase 2 → Phase 3 translation isn't guaranteed. The glucagon mechanism is theoretically sound but the history of metabolic drugs is littered with Phase 2 surprises that didn't replicate. Cautiously very excited..."
"Lost 6kg in 8 weeks which is faster than tirzepatide was for me. Side effects were more intense — nausea worse than Mounjaro at comparable weeks. Whether the product I have is actually retatrutide at the claimed concentration I genuinely don't know..."
"The synthesis is significantly more complex than semaglutide. Most vendors selling this do not have the capability to produce it correctly. I've seen testing of market samples that were severely underdosed or completely wrong compound..."
"If you have access to quality product and have already run tirzepatide: yes, interesting. If you're new to GLP-1s: start with tirzepatide. The incremental benefit over tirzepatide is real but not massive, and the quality risk is much higher..."