Retatrutide Peptide: What It Is and How to Track It
A plain-language look at the retatrutide peptide: what it is, how the triple agonist works, what the trials show, and how to keep your weekly routine on track, privately.
People often search for "retatrutide peptide" (or "retatrutide peptides," and sometimes just "reta") because retatrutide is, chemically, a peptide, and because many people who track it think of it as a weekly peptide injection. This page explains what that means, sticks to what published trials and the manufacturer have actually reported, and is general educational information, not medical advice. Retatrutide is investigational and not FDA-approved.
What is the retatrutide peptide?
Retatrutide (development code LY3437943) is a synthetic 39-amino-acid peptide developed by Eli Lilly. It carries a fatty-acid chain that binds to albumin in the blood, which extends its half-life to roughly 6 days and supports once-weekly dosing. In short, it is a lab-made peptide engineered to stay active in the body for about a week per injection.
How does it work? The triple agonist
What makes retatrutide unusual is that a single peptide activates three receptors at once: GLP-1, GIP, and glucagon. GLP-1 and GIP are the incretin pathways used by existing medicines, while the added glucagon activity is thought to increase energy expenditure. Single-receptor peptides like semaglutide target GLP-1 only, and dual agonists like tirzepatide target GLP-1 and GIP, so retatrutide's triple action is the main thing that distinguishes it.
What have the trials shown?
In its Phase 2 obesity trial, published in the New England Journal of Medicine, the 12 mg once-weekly dose produced a mean weight reduction of about 24.2% at 48 weeks, with roughly a quarter of participants on the top dose losing more than 30% of their body weight. The Phase 2 doses studied were 1, 4, 8, and 12 mg weekly. Retatrutide has since moved into the large Phase 3 TRIUMPH program: TRIUMPH-4 reported topline results in late 2025, and TRIUMPH-1 reported in 2026 with about 28.3% mean weight loss at the 12 mg dose over 80 weeks.
As with other incretin-based medicines, the most common side effects reported in trials were gastrointestinal (nausea, diarrhea, vomiting, and constipation), mostly during dose escalation. Phase 2 also noted a dose-dependent increase in heart rate that peaked around 24 weeks. Because retatrutide is still investigational, its full safety profile is still being characterized.
Is the retatrutide peptide FDA approved?
No. As of 2026, retatrutide is not approved by the FDA and cannot be prescribed as an approved medicine. It remains in Phase 3 trials while Eli Lilly completes its program and prepares a regulatory submission. Anything sold as "retatrutide" outside of a formal clinical trial is not an FDA-approved medicine and may carry safety and quality risks. If you are interested in retatrutide, that is a conversation to have with a qualified healthcare provider.
How to track your retatrutide peptide with RetaPal
If you and your provider have decided on a weekly routine, keeping a clean record helps you stay consistent and gives your provider a clear picture. RetaPal is a private retatrutide peptide tracker built for exactly this: log each weekly dose in one tap, watch the countdown to your next injection, turn on optional reminders, and record quick hunger check-ins between doses. Everything stays on your device, with no account and no cloud.
One thing RetaPal deliberately does not do: it never recommends, calculates, or suggests a dose. You enter the dose you took, based on your prescription or your provider's instructions. RetaPal is a log and reminder, nothing more.
Retatrutide peptide FAQ
Is retatrutide a peptide?
Yes. Retatrutide is a synthetic peptide: a 39-amino-acid molecule with a fatty-acid chain that helps it last about a week in the body. It is designed as a single peptide that activates three receptors at once.
What is retatrutide peptide?
"Retatrutide peptide" simply refers to retatrutide itself, which is a peptide medicine. It is an investigational once-weekly injectable developed by Eli Lilly (code name LY3437943) that is being studied for weight management and type 2 diabetes. It is often shortened to "reta" in online communities. It is not FDA-approved.
What kind of peptide is retatrutide?
It is a triple agonist. Retatrutide activates the GLP-1, GIP, and glucagon receptors with one molecule, which is what sets it apart from single-receptor GLP-1 peptides like semaglutide and dual GLP-1/GIP agonists like tirzepatide.
Is retatrutide peptide FDA approved?
No. As of 2026 retatrutide is investigational and not approved by the FDA. It is in Phase 3 trials (the TRIUMPH program) and is not available by prescription. Any product sold as "retatrutide" outside of a clinical trial is not an FDA-approved medicine.
How is retatrutide taken?
In its trials, retatrutide is given as a once-weekly subcutaneous injection. Its roughly 6-day half-life is what supports the once-a-week schedule.
Can RetaPal calculate my retatrutide peptide dose?
No, and it never will. RetaPal is a private log and reminder only. It does not recommend, calculate, or suggest doses. You enter the dose you took based on your prescription or your healthcare provider's instructions.
References
The figures on this page are drawn from the primary sources below and reflect published trials and Eli Lilly disclosures as of 2026.
- Retatrutide Phase 2 obesity trial (Jastreboff et al., 2023) — New England Journal of Medicine
- Retatrutide mechanism, structure, and half-life — Eli Lilly Medical
- TRIUMPH-1 Phase 3 obesity topline results (2026) — Eli Lilly
- TRIUMPH-4 Phase 3 obesity and osteoarthritis results — Eli Lilly
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RetaPal logs every dose, counts down to your next injection, and keeps it all private on your device. It never recommends or calculates doses.
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