What is retatrutide?
Retatrutide (LY3437943) is being developed by Eli Lilly. It is a triple incretin receptor agonist - meaning it activates three hormone receptors simultaneously:
- GIP receptor (glucose-dependent insulinotropic polypeptide) - enhances insulin secretion, promotes fat storage regulation
- GLP-1 receptor (glucagon-like peptide-1) - slows gastric emptying, suppresses appetite, improves insulin sensitivity
- Glucagon receptor - increases energy expenditure, promotes fat burning from the liver
By combining all three mechanisms, retatrutide produces weight loss through multiple complementary pathways that single-agonist (semaglutide) and dual-agonist (tirzepatide) drugs cannot achieve.
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What the Phase 2 trial showed
The Phase 2 trial (published NEJM, 2023) was significant:
- 338 adults with obesity, no diabetes
- Dose groups: 1mg, 4mg, 8mg, 12mg weekly, or placebo
- Duration: 48 weeks
- At the highest dose (12mg): average weight loss of 24.2% of body weight
- At 8mg: average weight loss of 22.8%
- Placebo: 2.1% weight loss
For context: semaglutide (Wegovy) produces approximately 15% weight loss in trials; tirzepatide (Zepbound) produces approximately 20-22%.
Retatrutide's results were the highest recorded for any weight loss drug in a randomized controlled trial at the time of publication.
Important caveat: These are Phase 2 results. Phase 3 trials are ongoing and needed before FDA approval. Phase 2 trials are designed to establish dosing and efficacy signal, not to make definitive safety and efficacy claims. Phase 3 results will be larger, longer, and more definitive.
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Where is retatrutide in the approval process?
As of mid-2026:
- Phase 3 trials are underway (TRIUMPH-1 and related trials)
- FDA approval is not expected before 2027 at the earliest based on typical trial timelines
- Retatrutide is not yet FDA-approved as a branded medication
This means it is not available through licensed US pharmacies as an approved drug.
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Can US patients access retatrutide now?
Some compounding pharmacies are producing retatrutide as a compounded peptide, available via physician prescription. The situation is similar to early compounded semaglutide before FDA approval.
What this means:
- Compounded retatrutide is being offered by some US telehealth clinics
- It requires a physician consultation and prescription
- It is compounded by 503A pharmacies under physician oversight
- It is not FDA-approved and does not have the clinical track record of approved GLP-1 medications
- Quality varies by pharmacy - ensuring your clinic uses an accredited compounding pharmacy matters
Who might consider it:
- Patients who have not achieved adequate results on semaglutide or tirzepatide
- People who have read the Phase 2 data and want to discuss it with a physician
- Those in physician-supervised programs where the prescriber is comfortable with the evidence base
Who should wait:
- Most patients seeking GLP-1 therapy for the first time are better served starting with FDA-approved options (semaglutide or tirzepatide) that have more extensive safety data
- The 24% weight loss figure from Phase 2 is compelling but comes from a relatively small, short trial
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Retatrutide vs. tirzepatide vs. semaglutide
| Semaglutide (Wegovy) | Tirzepatide (Zepbound) | Retatrutide | |
|---|---|---|---|
| Receptor targets | GLP-1 | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| FDA status | Approved | Approved | Phase 3 trials |
| Avg. weight loss | ~15% | ~20-22% | ~24% (Phase 2) |
| Availability | Widely available | Widely available | Compounded only |
| Evidence base | Extensive | Strong | Phase 2 only |
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What to ask a physician about retatrutide
If you are interested in discussing retatrutide with a physician:
- 1What Phase 3 trial data is available now?
- 2Is the compounding pharmacy you work with accredited?
- 3How does retatrutide compare to tirzepatide for a patient like me?
- 4What monitoring protocol do you use for retatrutide patients?
- 5What is the titration schedule?
A physician who can answer these questions clearly is operating thoughtfully. One who cannot explain the evidence base or pharmacy sourcing should be viewed cautiously.
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Finding a clinic that offers retatrutide
Browse US clinics that may offer retatrutide including telehealth programs with access to compounded peptides.
Browse weight loss clinics by state: California - Texas - Florida - New York - Illinois - browse all states.
Related guides: Semaglutide vs. tirzepatide - which is right for you? - GLP-1 clinic near me guide - Compounded semaglutide in 2026