Last medically reviewed: 2026-04-27 by GLP3 Planner editorial. References inline as available.
⚠️ Investigational Compound
Retatrutide (also called GLP-3 or "reta") is in Phase 3 clinical trials. It is not yet FDA-approved. Eli Lilly expects to submit for FDA approval in 2026, with approval possible in 2027. This chart shows clinical trial protocols from published studies.
Key Takeaways
- Starting dose: 2 mg once weekly for 4 weeks
- Titration pace: Increase every 4 weeks: 2 → 4 → 8 → 12 mg
- Maximum dose: 12 mg weekly (Phase 2/3 clinical trial protocol)
- Total ramp-up: ~16 weeks to reach maximum dose
- Mechanism: Triple agonist (GLP-1 + GIP + Glucagon), the only triple-agonist in late-stage trials
- Weight loss: Up to 24.2% at 48 weeks (Phase 2) and 28.7% at 68 weeks (Phase 3 TRIUMPH-4)
GLP-3 Retatrutide Dosage Chart
Free printable reference chart showing the retatrutide (GLP-3) clinical trial titration schedule from 2 mg to 12 mg weekly. Retatrutide is the first triple-agonist GLP-1/GIP/Glucagon medication in Phase 3 trials, made by Eli Lilly.
🧬 What Is Retatrutide (GLP-3)?
Retatrutide is often called "GLP-3" in online communities because it targets three receptors: GLP-1, GIP, and Glucagon. The glucagon component increases energy expenditure and fat oxidation, a mechanism unique to retatrutide that semaglutide (GLP-1 only) and tirzepatide (GLP-1/GIP) lack.
Phase 2 trial: up to 24.2% weight loss at 48 weeks. Phase 3 TRIUMPH-4: 28.7% at 68 weeks. Manufactured by Eli Lilly.
Printable GLP-3 Retatrutide Dosage Chart
This chart shows the titration protocol used in Eli Lilly's Phase 2 clinical trials, published in the New England Journal of Medicine. Each dose was held for 4 weeks before escalating. The Phase 3 TRIUMPH trials use a similar protocol.
Week-by-Week Retatrutide Titration Schedule
The table below shows the dose escalation protocol used in Phase 2 and Phase 3 retatrutide clinical trials. The protocol uses 4-week intervals at each dose, reaching the maximum 12 mg dose at week 13.
Want your own dates? The free retatrutide titration calculator turns your starting dose, target dose, and step interval into a week-by-week schedule with calendar step-up dates.
| Phase | Weeks | Dose | Purpose |
|---|---|---|---|
| Initiation | 1–4 | 2 mg | Below therapeutic range. Builds GI tolerance to triple-agonist activity. |
| Escalation 1 | 5–8 | 4 mg | First therapeutic dose. Appetite suppression and early weight loss begin. |
| Escalation 2 | 9–12 | 8 mg | Strong therapeutic effect. Significant weight loss and metabolic improvements. |
| Maximum | 13+ | 12 mg | Maximum trial dose. Highest weight loss and metabolic benefit. |
⚠️ Note: Phase 2 trials also tested a 1 mg starting dose, which showed modest results. The 2 mg → 4 mg → 8 mg → 12 mg protocol was the most effective and forms the basis for Phase 3 trials (TRIUMPH programme).
What to Expect at Each Dose Level
Based on the Phase 2 NEJM study (Jastreboff et al., 2023) and the TRIUMPH-4 Phase 3 results.
2 mg — Weeks 1–4
Introductory dose to establish tolerability. Your body is adapting to GLP-1, GIP, and glucagon receptor activation at the same time. Expect mild nausea in the first 1–2 weeks. Some appetite suppression may occur but weight loss is minimal.
Phase 2 weight loss (48 weeks): 8.7% at 2 mg maintenance
4 mg — Weeks 5–8
First dose where therapeutic effects become clinically meaningful. Appetite suppression strengthens noticeably. The glucagon component begins to increase energy expenditure. GI side effects may worsen temporarily during this escalation but usually stabilise within 2 weeks.
Phase 2 weight loss (48 weeks): 17.1% at 4 mg maintenance
8 mg — Weeks 9–12
Strong therapeutic dose with substantial appetite suppression and metabolic improvements. Fat oxidation increases significantly due to glucagon receptor activation. This dose level shows the most dramatic change in body composition.
Phase 2 weight loss (48 weeks): 22.8% at 8 mg maintenance
12 mg — Weeks 13+
Maximum trial dose. In Phase 2, the 12 mg group lost an average of 24.2% body weight over 48 weeks. Phase 3 TRIUMPH-4 showed 28.7% at 68 weeks, nearly double what semaglutide 2.4 mg achieves. This is the highest average weight loss of any GLP-1 class medication tested to date.
Phase 2 weight loss (48 weeks): 24.2% | Phase 3 (68 weeks): 28.7%
Side Effects by Dose Level
Side effects follow a dose-dependent pattern. Retatrutide can produce side effects from all three receptor pathways (GLP-1, GIP, and glucagon). Most GI symptoms are temporary and peak during dose escalations. For a complete guide, see our retatrutide side effects guide.
| Side Effect | 4 mg | 8 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 25% | 36% | 46% | 9% |
| Diarrhoea | 22% | 28% | 34% | 11% |
| Vomiting | 8% | 10% | 13% | 2% |
| Constipation | 6% | 12% | 16% | 4% |
| Decreased appetite | 11% | 15% | 22% | 3% |
Source: Phase 2 trial data (Jastreboff et al., NEJM 2023). Phase 3 side effect profiles are expected to be similar.
💡 Tip: The glucagon receptor component may cause slightly higher rates of nausea compared to semaglutide or tirzepatide at similar efficacy levels. However, discontinuation rates in Phase 2 were low (~6% at 12 mg), which suggests side effects were manageable for most participants.
How Does GLP-3 Compare to Tirzepatide and Semaglutide?
Retatrutide's triple-agonist mechanism produces higher weight loss than existing medications. Here is how the dosing and results compare:
| Retatrutide | Tirzepatide | Semaglutide | |
|---|---|---|---|
| Mechanism | GLP-1 + GIP + Glucagon | GLP-1 + GIP | GLP-1 only |
| Starting dose | 2 mg | 2.5 mg | 0.25 mg |
| Max dose | 12 mg | 15 mg | 2.4 mg maintenance / 7.2 mg max |
| Titration steps | 4 levels | 6 levels | 5 levels |
| Time to max | ~16 weeks | ~20 weeks | ~16 weeks |
| Max weight loss | 24.2–28.7% | 20.9% | 14.9% |
| FDA status | Phase 3 trials | FDA-approved (2022) | FDA-approved (2017) |
For detailed comparisons, see retatrutide vs tirzepatide. You can also compare dosing protocols with the tirzepatide dosage chart and semaglutide dosage chart.
Visualise Your Retatrutide Levels
Our free calculator shows peak, trough, and steady-state drug levels across your entire dosing schedule.
Open Retatrutide Calculator →How to Use This Chart
- Understand the status: Retatrutide is investigational and not FDA-approved. This chart shows clinical trial protocols, not a prescription.
- Track your protocol: If you are using retatrutide under medical supervision, use this chart to track your current dose and upcoming escalations.
- Plan for side effects: Each dose increase can cause temporary GI symptoms. Stock up on bland foods and clear liquids before escalation weeks.
- See drug levels: Use the retatrutide calculator to see how drug concentration builds between doses and across your dosing schedule.
- Convert to syringe units: Turn any mg dose on this chart into exact insulin units with the retatrutide dose-to-units calculator.
- Consult your provider: Always follow your prescriber's instructions. Your personal protocol may differ from the standard trial schedule.
Can I Microdose Retatrutide?
Some users split their weekly retatrutide dose into smaller, more frequent injections to reduce peak-related side effects and maintain more stable drug levels. This approach isn't used in clinical trials but is practised by some prescribers, particularly with compounded retatrutide.
Our retatrutide microdosing guide covers split-dosing protocols with pharmacokinetic modelling showing how drug levels differ between weekly and split-dose approaches.
Stay Updated on Retatrutide
Ask our AI guide about Phase 3 trial results, expected approval timeline, and how retatrutide compares to other GLP-1 medications.
References
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. PubMed
- Eli Lilly. Lilly's retatrutide achieved 28.7% weight reduction at 68 weeks in TRIUMPH-4. Press release, 2024. ClinicalTrials.gov
- Rosenstock J, Frias JP, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes. Lancet. 2023;402(10401):529-544. PubMed
- ClinicalTrials.gov. TRIUMPH Programme — Eli Lilly retatrutide Phase 3 studies. ClinicalTrials.gov
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss. Cell Metab. 2022;34(9):1234-1247. PubMed
Related Resources
Retatrutide Hub
Complete retatrutide guide: mechanism, trial data, side effects, and forecasts.
Retatrutide Dosing Guide
Clinical trial protocols, pharmacokinetics, and detailed dosing information.
Retatrutide Side Effects
Phase 2 side effect data with management strategies.
Retatrutide vs Tirzepatide
Head-to-head comparison of the triple vs dual agonist.
Microdosing Retatrutide
Split dosing strategies with pharmacokinetic modelling.
Tirzepatide Dosage Chart
Mounjaro & Zepbound dosage reference with printable chart.
Medical Disclaimer: Retatrutide is an investigational compound and is not FDA-approved. This chart shows clinical trial protocols and is for informational purposes only. It does not constitute medical advice, diagnosis, or treatment. Do not self-administer retatrutide based on this chart. If you are enrolled in a clinical trial, follow your trial protocol. Consult a qualified healthcare provider before using any investigational medication.