Overview
Overview
Retatrutide is an investigational triple-receptor agonist peptide (targets GLP-1, GIP, and glucagon receptors) under development for obesity and type 2 diabetes[1][2]. Phase 2 trials demonstrated remarkable weight-loss efficacy, with patients losing up to 24% of body weight at 48 weeks on higher doses[3][4]. This educational protocol presents a once-weekly subcutaneous approach with gradual titration to minimize gastrointestinal side effects. Reconstitute: Add 1.0 mL bacteriostatic water → ~10.
- Category
- Weight Loss
- Routes
- subcutaneous
Mechanism
Retatrutide
Mechanism of action
Mechanism of action
Retatrutide acts on three hormone pathways at the same time: GLP-1, GIP, and glucagon. Most other research peptides in this class only act on one or two. The simplest way to picture it: one pathway helps the body feel full, one helps it handle blood sugar and stored fuel, and one may push energy use up. This is the same general pathway used by semaglutide. It slows digestion and helps people feel full longer, which is one reason retatrutide can reduce appetite. Researchers coming from GLP-1 work will recognize this part of the mechanism. GIP is short for glucose-dependent insulinotropic polypeptide. It is part of why retatrutide is studied as a broader metabolic compound rather than only an appetite tool. In plain English, it helps the body manage blood sugar and how it stores energy. This is the third lever, and it is what separates retatrutide from tirzepatide. Glucagon receptor activity is linked to higher energy expenditure and fat oxidation. It is a likely reason why the weight loss and liver fat numbers in trials look stronger than older single- or dual-pathway compounds. Structurally, retatrutide is a 39-amino acid single-chain peptide with a C20 fatty diacid attachment. That attachment helps it bind to albumin in the blood. The longer circulation time is the technical reason for the ~6-day half-life and once-weekly dosing.
Key research findings
- 01
Retatrutide (LY3437943) is a once-weekly triple agonist at GIP, GLP-1, and glucagon receptors (mechanistic / human study).
- 02
In a Phase 2 trial in adults with obesity, retatrutide produced large dose-dependent body-weight reductions, up to roughly a quarter of body weight at 48 weeks at the highest dose (human study, Phase 2; Jastreboff et al., New England Journal of Medicine, 2023).
- 03
Phase 3 TRIUMPH program readouts (2025-2026) reported substantial weight reduction, with averages reported up to around 30% in primary obesity trials and meaningful reductions in a trial that also included knee osteoarthritis (human study, Phase 3).
- 04
The triple mechanism is researched for combined effects on appetite, glycemic control, and energy expenditure/hepatic fat (mechanistic).
- 05
Gastrointestinal effects were the most commonly observed effects in research (human study observation).
Primary source: Human evidence - Phase 3 TRIUMPH-1 (Eli Lilly, May 21, 2026): 2,339 adults with obesity or overweight without diabetes. The 12 mg dose produced 28.3% average body weight loss at 80 weeks, and a higher-BMI two-year subgroup reached 30.3% average loss at 104 weeks. Results are topline only; full peer-reviewed data has not been published yet. Human evidence - Phase 3 TRIUMPH-4 (Eli Lilly, December 11, 2025): Adults with obesity and knee osteoarthritis. Average 28.7% body weight loss at 68 weeks at the 12 mg dose (about 71.2 lbs / 32.3 kg average loss). WOMAC pain score improved by 4.5 points. Dysesthesia reported in about 20.9% at the highest dose. Human evidence - Phase 3 TRANSCEND-T2D-1 (Eli Lilly, March 19, 2026): 537 adults with type 2 diabetes, randomized 1:1:1:1 to retatrutide 4, 9, or 12 mg or placebo. A1C reduction of 1.7-2.0% across doses at 40 weeks. Average 16.8% body weight loss at 12 mg (about 36.6 lbs). No weight plateau reached at 40 weeks. Detailed results scheduled for the American Diabetes Association Scientific Sessions, June 2026. Human evidence - Phase 2 NEJM (Jastreboff et al., 2023): 338 adults with obesity but no diabetes. 12 mg: -24.2% body weight at 48 weeks. 8 mg: -22.8%. 4 mg: -17.5%. 100% of 8 mg and 12 mg participants lost at least 5%; 83% in the 12 mg arm lost at least 15%. Human evidence - Phase 2 type 2 diabetes (Rosenstock et al., Lancet 2023): Adults with type 2 diabetes, 36 weeks. Up to -16.9% weight loss. HbA1c improved by -2.2%. 82% reached HbA1c at or below 6.5%. Human evidence - Phase 2 MASLD substudy (Sanyal et al., Nature Medicine 2024): Adults with MASLD and at least 10% liver fat. Up to 82% relative reduction in liver fat at 24 weeks. Pharmacokinetics (Coskun et al., Cell Metabolism 2022): Phase 1 PK data established the ~6-day half-life and once-weekly dosing rationale. Albumin binding via the C20 fatty diacid attachment is the technical mechanism. Evidence boundary
Pharmacokinetic profile
Single-dose plasma curve over 24h. Shaded band = commonly-cited therapeutic window. Illustrative only.
Protocol Reference
Protocol reference
Commonly cited research range: 2–12 mg, weekly.
Reference figures reported in the research literature — not a dosing recommendation. For interactive vial math and scheduling, see the Calculator and Schedule tabs.
Cited protocol & reconstitution guide
Source-backed reference fields by phase, including any volume fields authored in the cited guide.
Weeks 1–4 (Initiation)
1 mg
Weeks 5–8 (Early escalation)
2 mg
Weeks 9–12 (Mid escalation)
4 mg
Weeks 13–16 (High escalation)
6 mg
Weeks 17–20
9 mg
| Phase | Reference amount | Units / volume |
|---|---|---|
| Weeks 1–4 (Initiation) | 1 mg | 10 units (0.10 mL) |
| Weeks 5–8 (Early escalation) | 2 mg | 20 units (0.20 mL) |
| Weeks 9–12 (Mid escalation) | 4 mg | 40 units (0.40 mL) |
| Weeks 13–16 (High escalation) | 6 mg | 60 units (0.60 mL) |
| Weeks 17–20 | 9 mg | 90 units (0.90 mL) |
Titration protocol
- Weeks 1–4Start1 mg
Starting dose. Hold 4 weeks before stepping up. Inject once per week on the same day each week and rotate injection sites. Missed by 5 days or fewer, take when remembered; more than 5 days, skip and resume the next scheduled day without doubling.
- Weeks 5–8Build2 mg
Hold 4 weeks at this step before escalating. Same weekly day; continue rotating sites.
- Weeks 9–12Build4 mg
Hold 4 weeks and review before the next step. Highest step drawable from a single 5 mg vial.
- Weeks 13–16Build6 mg
Intermediate step added in the Phase 3 ladder; the Phase 2 ladder stepped from 4 mg straight to 8 mg. Exceeds the content of one 5 mg vial — additional vials required.
- Weeks 17–20Build9 mg
Phase 3 target step for many TRIUMPH arms. Hold 4 weeks. Exceeds the content of one 5 mg vial — additional vials required.
- Weeks 21+Maintenance12 mg
Maximum dose studied. Trial protocols allowed staying at the current dose an extra 2–4 weeks when GI symptoms persisted. Exceeds the content of one 5 mg vial — additional vials required; split any draw over 1.0 mL into equal injections at separate sites.
Storage & Handling
Storage requirements(typical for most peptides)
Can be stored for extended periods. Protect from moisture.
Store in refrigerator door. Never freeze after reconstitution.
Label vials with reconstitution date. Discard if cloudy.
Reconstitution steps
- 01🌡️Bring vials to room temperature: let the lyophilized retatrutide vial and the bacteriostatic water sit at room temperature before mixing.
- 02🧴Clean both vial stoppers: wipe each with an alcohol swab and let them dry fully.
- 03💉Draw 1 mL bacteriostatic water into a sterile syringe — this 10 mg vial yields 10 mg/mL.
- 04💧Inject down the vial wall: push the bacteriostatic water slowly down the inside wall; do not spray it directly into the powder.
- 05🔄Swirl gently until the solution is clear; do not shake.
- 06🏷️Refrigerate: store at 35.6–46.4 °F (2–8 °C), protected from light, and plan to use within 2–4 weeks. Frozen single-use aliquots at -4 °F (-20 °C) keep 3–4 months; avoid repeat freeze-thaw.
- 07❄️Important: This guide is for educational purposes only and is not medical advice. Retatrutide is supplied for research use only. All figures reflect published trial protocols.
- 08💉This 10mg vial covers the first 5 steps of the schedule; later steps exceed one vial.
Additional storage notes
-4F (-20C) or below (freezer) — Long-term, up to 12+ months
35.6-46.4F (2-8C) (refrigerator) — Several months
Room temperature short-term — Stable for several weeks; powder tolerates short-term temperature swings
35.6-46.4F (2-8C) (refrigerator) — Use within 2-4 weeks; protect from light
-4F (-20C) (frozen aliquots) — Up to 3-4 months; avoid repeat freeze-thaw
Clinical Evidence
Clinical evidence
Phase 2 clinical trials report substantial body-weight reduction; it remains investigational and under development.
Human evidence - Phase 3 TRIUMPH-1 (Eli Lilly, May 21, 2026): 2,339 adults with obesity or overweight without diabetes. The 12 mg dose produced 28.3% average body weight loss at 80 weeks, and a higher-BMI two-year subgroup reached 30.3% average loss at 104 weeks. Results are topline only; full peer-reviewed data has not been published yet. Human evidence - Phase 3 TRIUMPH-4 (Eli Lilly, December 11, 2025): Adults with obesity and knee osteoarthritis. Average 28.7% body weight loss at 68 weeks at the 12 mg dose (about 71.2 lbs / 32.3 kg average loss). WOMAC pain score improved by 4.5 points. Dysesthesia reported in about 20.9% at the highest dose. Human evidence - Phase 3 TRANSCEND-T2D-1 (Eli Lilly, March 19, 2026): 537 adults with type 2 diabetes, randomized 1:1:1:1 to retatrutide 4, 9, or 12 mg or placebo. A1C reduction of 1.7-2.0% across doses at 40 weeks. Average 16.8% body weight loss at 12 mg (about 36.6 lbs). No weight plateau reached at 40 weeks. Detailed results scheduled for the American Diabetes Association Scientific Sessions, June 2026. Human evidence - Phase 2 NEJM (Jastreboff et al., 2023): 338 adults with obesity but no diabetes. 12 mg: -24.2% body weight at 48 weeks. 8 mg: -22.8%. 4 mg: -17.5%. 100% of 8 mg and 12 mg participants lost at least 5%; 83% in the 12 mg arm lost at least 15%. Human evidence - Phase 2 type 2 diabetes (Rosenstock et al., Lancet 2023): Adults with type 2 diabetes, 36 weeks. Up to -16.9% weight loss. HbA1c improved by -2.2%. 82% reached HbA1c at or below 6.5%. Human evidence - Phase 2 MASLD substudy (Sanyal et al., Nature Medicine 2024): Adults with MASLD and at least 10% liver fat. Up to 82% relative reduction in liver fat at 24 weeks. Pharmacokinetics (Coskun et al., Cell Metabolism 2022): Phase 1 PK data established the ~6-day half-life and once-weekly dosing rationale. Albumin binding via the C20 fatty diacid attachment is the technical mechanism. Evidence boundary
- 01Retatrutide (LY3437943) is a once-weekly triple agonist at GIP, GLP-1, and glucagon receptors (mechanistic / human study).
- 02In a Phase 2 trial in adults with obesity, retatrutide produced large dose-dependent body-weight reductions, up to roughly a quarter of body weight at 48 weeks at the highest dose (human study, Phase 2; Jastreboff et al., New England Journal of Medicine, 2023).
- 03Phase 3 TRIUMPH program readouts (2025-2026) reported substantial weight reduction, with averages reported up to around 30% in primary obesity trials and meaningful reductions in a trial that also included knee osteoarthritis (human study, Phase 3).
- 04The triple mechanism is researched for combined effects on appetite, glycemic control, and energy expenditure/hepatic fat (mechanistic).
- 05Gastrointestinal effects were the most commonly observed effects in research (human study observation).
Evidence maturity varies by compound; much peptide research is preclinical (in vitro or animal-model). Where human data are limited, findings should be read as research observations, not clinical conclusions.
References
Literature references
Published research articles and sources related to Retatrutide.
- 01The Lancet (2023) — Rosenstock J, et al. Retatrutide for type 2 diabetes: Phase 2 trial results (36-week study, HbA1c reductions, weight loss) View Sourceet al. (2023)
- 02New England Journal of Medicine (2023) — Jastreboff AM, et al. Triple-hormone-receptor agonist Retatrutide for obesity: Phase 2 trial (48-week study, up to 24% weight loss) View Sourceet al. (2023)
- 03American Diabetes Association (2023) — ADA Press Release: Novel agent Retatrutide results in substantial weight reduction (83rd Scientific Sessions, Phase 2 data) View Sourceet al. (2023)
- 04ADA Meeting News (2023) — Phase 2 trial results: benefits of Retatrutide in obesity, type 2 diabetes, NASH (83rd ADA Scientific Sessions coverage) View Sourceet al. (2023)
- 05ClinicalTrials.gov — Study of Retatrutide (LY3437943) in adults with obesity (NCT04881760; protocol details, dosing regimens) View Source
- 06Current Obesity Reports (2025) — Hamza M, et al. Triple agonism based therapies for obesity (review; titration strategies, GI side effect management) View Sourceet al. (2025)
- 07Cell Metabolism (2022) — Coskun T, et al. LY3437943 (Retatrutide): discovery to clinical proof of concept (triple GLP-1/GIP/glucagon agonist, preclinical mechanism) View Sourceet al. (2022)
- 08Nature Reviews Endocrinology (2024) — Multi-receptor agonists for metabolic disease (mechanism of GLP-1/GIP/glucagon co-activation) View Sourceet al. (2024)
- 09Diabetes Care (2024) — Incretin-based therapies: GLP-1, GIP, and glucagon receptor pharmacology (metabolic pathways, energy expenditure) View Sourceet al. (2024)
- 10NEJM (2023) — Supplementary Material — Jastreboff et al. obesity trial: cardiometabolic markers, liver fat reduction, lipid profiles View Sourceet al. (2023)
- 11Hepatology (2024) — Triple agonists in NAFLD/NASH: hepatic steatosis resolution (preclinical and clinical evidence) View Sourceet al. (2024)
- 12The Lancet (2023) — Supplementary Data — Rosenstock et al. diabetes trial: adverse event profiles, GI tolerability, titration schedules View Sourceet al. (2023)
- 13CDC — Vaccine administration: subcutaneous route (angle/site guidance; no aspiration required) View Source
- 14Johns Hopkins Arthritis Center — How to give a subcutaneous injection (technique, site rotation, sharps disposal) View Source
- 15NCBI Bookshelf — Administration of medication: subcutaneous injections (aseptic technique, preparation) View Source
- 16GenScript Peptide Services — Peptide storage and handling guidelines (lyophilized and reconstituted storage conditions, stability) View Source
- 17Journal of Pharmaceutical Sciences (2018) — Stability of peptides during freeze-thaw cycles (best practices for aliquoting and storage) View Sourceet al. (2018)
- 18Pure Lab Peptides — Retatrutide (10 mg) product page (quality specifications, batch documentation, supplier information) View Source
Observed Effects
Observed effects in cited research
Common gastrointestinal effects (Phase 2 NEJM)
- NauseaUp to 25%
- DiarrheaUp to 23%
- VomitingUp to 26%
- ConstipationUp to 16%
- GI symptoms were most common during dose escalation and were usually mild to moderate. Source: Jastreboff et al., NEJM 2023.
Dysesthesia signal (Phase 3)
- TRIUMPH-4 topline results, released December 11, 2025, reported dysesthesia in about 20.9% of participants at the highest dose. Dysesthesia means unusual skin sensitivity, tingling, or tenderness to touch. It is the most distinct safety signal that separates retatrutide from older GLP-1 class compounds.
Cardiovascular and metabolic signals
- Resting heart rate increased by about 5-10 bpm on average. It peaked near week 24 and eased by weeks 36-48.
- Phase 2 reported no increase in serious cardiovascular events.
- Temporary ALT/AST elevations occurred in a minority of participants and were generally tied to dose increases.
- Injection site reactions (redness, itching, small nodules) were observed in roughly 5-15% of participants.
Study and material context
Discontinuation
- In Phase 2, 6-16% of participants stopped because of adverse events versus 0% on placebo. Slow titration improved protocol compliance. That is the main practical reason the protocol uses a 4-week climb at each step.
Quality control matters
- Retatrutide is research-grade and not standardized for human use. COA verification, batch testing, and storage matter. Bad reconstitution, repeated freeze-thaw cycles, or contaminated BAC water can show up as injection site issues that look like observed effects.
Research Considerations
Research considerations
Research Use Only - not for human or veterinary therapeutic use. Investigational compound currently in clinical development; not approved for general use. Consult a licensed healthcare professional for any clinical decisions.
- Personal or family history of medullary thyroid carcinoma or MEN 2.
- History of pancreatitis or gallbladder disease.
- Severe kidney or liver disease.
- Diabetic retinopathy or active retinal disease.
- Severe GI conditions (gastroparesis, IBD flare).
- Active cardiovascular disease, recent heart attack, or unstable angina.
- Use of insulin or sulfonylureas (hypoglycemia risk).
Factors noted in the research literature; not patient-specific medical advice.
Regulatory Status
Regulatory status
RUO
Comparisons
Comparisons
| Compound | Mechanism | Route | Status |
|---|---|---|---|
| Retatrutidethis | An investigational triple-receptor agonist targeting GLP-1, GIP, and glucagon receptors, combining appetite regulation, insulinotropic activity, and increased energy expenditure. | subcutaneous | Investigational / RUO |
| Semaglutide | Activates GLP-1 receptors to increase insulin secretion, slow gastric emptying, and reduce appetite through central mechanisms. | subcutaneous | Investigational / RUO |
| SLU-PP-332 | A synthetic pan-agonist of estrogen-related receptors (ERR alpha/beta/gamma) studied for activation of an aerobic-exercise-like gene program and increased oxidative metabolism. | — | Investigational / RUO |
| Survodutide | An investigational long-acting dual agonist of GLP-1 and glucagon receptors studied for appetite regulation and increased energy expenditure. | subcutaneous | Investigational / RUO |
| Tirzepatide | Activates both GIP and GLP-1 receptors, providing synergistic effects on insulin secretion, glucose control, and appetite regulation. | subcutaneous | Investigational / RUO |
| Selank | Modulates GABA and serotonin systems. Increases BDNF. Provides anxiolytic effects without sedation or cognitive impairment. | nasal, subcutaneous | Investigational / RUO |
| Semax | Increases BDNF expression, enhances dopamine and serotonin metabolism. Provides neuroprotection and cognitive enhancement. | nasal, subcutaneous | Investigational / RUO |
Attributes shown for research comparison only; not a statement of efficacy or therapeutic equivalence.
FAQ
Frequently asked questions
The starting dose of retatrutide in clinical trials is 1 mg once weekly for the first 4 weeks. The 1 mg starting point is designed for tolerance, not weight loss. The titration schedule then steps up every 4 weeks: 1 mg -> 2 mg -> 4 mg -> 6 mg -> 9 mg -> 12 mg in the Phase 3 TRIUMPH protocol.
Retatrutide's half-life is about 6 days (around 144 hours). That is why the protocol uses once-weekly dosing. After stopping, it takes roughly 5 half-lives (about 30 days) for the compound to clear the body. The technical reason for the long half-life is albumin binding via a C20 fatty diacid attachment.
In the Phase 2 NEJM trial (2023), participants on 12 mg lost an average of 24.2% of body weight at 48 weeks. In Phase 3 TRIUMPH-4 (Eli Lilly, December 11, 2025), the 12 mg arm averaged 28.7% body weight loss at 68 weeks. In Phase 3 TRIUMPH-1 (May 21, 2026), the 12 mg arm averaged 28.3% weight loss at 80 weeks, and a higher-BMI subgroup reached 30.3% at 104 weeks. Phase 3 TRANSCEND-T2D-1 (March 19, 2026) showed 16.8% loss at 12 mg over 40 weeks in adults with type 2 diabetes. Results are dose-dependent and individual outcomes vary.
Add bacteriostatic water based on the vial size and the concentration you want. Common mixes: 5 mg vial + 1.0 mL = 5 mg/mL; 10 mg vial + 2.0 mL = 5 mg/mL; 20 mg vial + 2.0 mL = 10 mg/mL; 24 mg vial + 2.4 mL = 10 mg/mL; 30 mg vial + 3.0 mL = 10 mg/mL. Inject the BAC water down the vial wall, swirl gently (do not shake), refrigerate at 35.6-46.4F (2-8C), and use within 2-4 weeks. Use the PepPal calculator for exact unit math.
No. As of June 2026, retatrutide is not FDA-approved. It is investigational and remains in Phase 3 trials. Eli Lilly has not submitted a New Drug Application. Analyst projections place possible approval in late 2027 or 2028, but those are estimates, not confirmed dates.
The most common observed effects are stomach-related: nausea, diarrhea, vomiting, and constipation, especially during dose escalation. In Phase 3 TRIUMPH-4, about 20.9% of participants at the highest dose reported dysesthesia, which means unusual skin sensitivity or tingling. Resting heart rate increased by about 5-10 bpm on average and eased over time. Slow titration was the main lever for tolerance.
Retatrutide is a triple agonist (GLP-1 + GIP + glucagon), tirzepatide is a dual agonist (GLP-1 + GIP), and semaglutide is a single agonist (GLP-1). Retatrutide has shown the highest weight loss numbers in trials so far (28.7% in Phase 3 TRIUMPH-4 vs 22.5% for tirzepatide in SURMOUNT-1 and 15.8% for semaglutide in STEP-1). Retatrutide is still investigational, while tirzepatide and semaglutide are FDA-approved.
Research-grade retatrutide is most commonly available in 5 mg, 10 mg, 20 mg, 24 mg, and 30 mg vial sizes. Vial size affects reconstitution math and how many doses each vial covers. The 10 mg and 24 mg formats are common in retail research catalogs.
Clinical trial protocols treated missed doses this way: if a scheduled weekly dose is missed and 5 or fewer days have passed, the dose can be taken when remembered. If more than 5 days have passed, skip it and resume on the next scheduled day. Doubling up is not recommended. This is the trial-protocol rule, not a personal medical recommendation.
Store reconstituted retatrutide at 35.6-46.4F (2-8C) (refrigerator), protected from light, and use within 2-4 weeks. Lyophilized (powder) vials are typically kept at -4F (-20C) for long-term storage. Avoid repeat freeze-thaw cycles. If long-term storage is needed for reconstituted solution, freeze single-use aliquots rather than the same vial over and over.
TRIUMPH is Eli Lilly's Phase 3 obesity-focused retatrutide program. It includes obesity studies and weight-related conditions like knee osteoarthritis (TRIUMPH-4), obstructive sleep apnea, chronic low back pain, cardiovascular and renal outcomes, and MASLD. The separate TRANSCEND-T2D Phase 3 program covers type 2 diabetes (TRANSCEND-T2D-1 reported topline results March 19, 2026).
The maximum dose studied in clinical trials is 12 mg once weekly. Phase 2 reported -24.2% body weight at 48 weeks at 12 mg, and Phase 3 TRIUMPH-4 reported up to -28.7% at 68 weeks at 12 mg. Higher doses have not been studied in published trials.
No. This page is an educational research reference. It is not medical advice and not a personal treatment plan. Retatrutide is investigational and not FDA-approved as of June 2026. Anyone considering use outside a clinical trial should talk to a qualified clinician.
Research-use notice
Research Use Only. This educational content and calculation support is intended for private research documentation. It does not provide medical advice, human-use directions, or claims of safety or effectiveness.