MEDICAL DISCLAIMER: Educational research guidelines only. Lyophilized peptides are investigational chemical compounds and are NOT approved for human consumption, diagnosis, or therapy. Consult a licensed physician before any research application.
Retatrutide Dosage Chart, Schedule & Reconstitution Protocol
Quickstart Highlights
Retatrutide (Eli Lilly LY3437943) is a once-weekly triple agonist that simultaneously activates the GLP-1, GIP and glucagon receptors — the only triple-incretin in advanced clinical development. The GLP-1 and GIP arms suppress appetite and improve glycemia, while the added glucagon arm increases resting energy expenditure and accelerates hepatic lipid oxidation, driving an unusually large fat-mass effect. The Phase 2 TRIUMPH-2 trial (Jastreboff et al., NEJM 2023) reported placebo-adjusted weight loss of 24.2% at 48 weeks on 12 mg, with a parallel Phase 2a MASH study showing roughly 82–86% reductions in liver fat [1][4]. Retatrutide remains investigational — it is not approved by FDA, EMA or any other regulator, with the Phase 3 TRIUMPH program (including the TRIUMPH-CVOT cardiovascular trial) still recruiting and topline obesity readouts not expected before 2026–2027.
Reconstitute: Add 1 mL bacteriostatic water → 5.0 mg/mL concentration.
Typical dose: 2–8 mg once weekly (gradual escalation over 8–12 weeks).
Easy measuring: At 5.0 mg/mL, 1 unit = 0.01 mL = 0.0500 mg (50 mcg) on a U-100 insulin syringe.
Storage: Lyophilized frozen at −20 °C; reconstituted refrigerated at 2–8 °C for up to 4 weeks[16].
Half-life: Terminal half-life of approximately 6 days driven by C20 fatty-acid acylation and albumin binding, supporting fixed once-weekly subcutaneous dosing with steady-state reached around week 4 [1].
Peak effect: Weight loss continues climbing through week 48 in TRIUMPH-2 with no clear plateau on the 12 mg arm, suggesting longer durations may extract additional benefit [1].
Regulatory status: Investigational research compound — not FDA, EMA or NMPA approved. Phase 3 TRIUMPH-3, TRIUMPH-4 and TRIUMPH-CVOT trials are ongoing, with anticipated obesity NDA submission in 2026–2027.
vs tirzepatide: Cross-trial comparisons place retatrutide at roughly 24% weight loss at 48 weeks vs tirzepatide's ~21% at 72 weeks — the added glucagon agonism appears to drive the gap, particularly on hepatic fat and energy expenditure.
Quick Protocol Navigation
Reconstitution Instruction & Mixing Step-by-Step
Lyophilized powder must be reconstituted carefully. Agitating peptide chains can shear disulfide bonds and render the peptide biologically inert.
Draw 1.0 mL bacteriostatic water with a sterile syringe.
Inject slowly down the vial wall; avoid foaming.
Gently swirl/roll until dissolved (do not shake).
Inject slowly; wait a few seconds before withdrawing the needle to ensure full dose delivery.
Do not aspirate for subcutaneous injections; inject slowly and steadily[13].
Interactive Retatrutide Syringe Calculator
Currently visualizing the 5 mg vial reconstituted with 1 mL bacteriostatic water. Adjust the target dose to dynamically render syringe units.
Reconstitution Calculation: 5mg dry powder in 1mL water yields 5.00 mg/mL. To evaluate a 250mcg dose, pull to 5.0 units (5 syringe ticks).
U-100 Syringe Representation
5.0 Units (5 Ticks)
Educational reference visual. Assumes standard U-100 insulin syringe where 1.0 mL volume = 100 units.
Titration & Dose Escalation Schedules
| Phase | Weekly Dose | Units (per injection) (mL) | Vials Needed |
|---|---|---|---|
| Weeks 1–4 | 2 mg (2000 mcg) | 40 units (0.40 mL) | 1 vial per dose |
| Weeks 5–8 | 4 mg (4000 mcg) | 80 units (0.80 mL) | 1 vial per dose |
| Weeks 9–12 | 6 mg (6000 mcg) | 120 units (1.20 mL) | 2 vials per dose** |
| Weeks 13+ | 8 mg (8000 mcg) | 160 units (1.60 mL) | 2 vials per dose** |
Administration guidelines: Refer to guidelines | 1 mL Reconstitution
| Phase | Weekly Dose | Units (per injection) (mL) | Vials Needed |
|---|---|---|---|
| Weeks 1–4 | 2 mg (2000 mcg) | 40 units (0.40 mL) | 1 vial per dose |
| Weeks 5–8 | 4 mg (4000 mcg) | 80 units (0.80 mL) | 1 vial per dose |
| Weeks 9–12 | 8 mg (8000 mcg) | 160 units (1.60 mL) | 2 vials per dose** |
| Weeks 13+ | 12 mg (12000 mcg) | 240 units (2.40 mL) | 3 vials per dose*** |
Administration guidelines: Refer to guidelines | 1 mL Reconstitution
Research Supplies Quantity Planner
Scientific mathematical planning of syringes, bacteriostatic water and dry vials needed for extended research blocks using the 5 mg vial.
Peptide Vials (Retatrutide, 5 mg each):
- check12 weeks (Standard to 6 mg): 10 vials
- check24 weeks (Standard to 8 mg): 29 vials
- check12 weeks (Aggressive to 8 mg): 12 vials
Insulin Syringes (U-100, 1 mL capacity):
- checkPer week: 1–3 syringes (depending on dose; higher doses require split injections)
- check12 weeks: 12–36 syringes
- check24 weeks: 24–72 syringes
Bacteriostatic Water (10 mL bottles): Use ~1.0 mL per vial for reconstitution.
- check12 weeks (10 vials): 10 mL → 1 × 10 mL bottle
- check24 weeks (29 vials): 29 mL → 3 × 10 mL bottles
Alcohol Swabs: One for the vial stopper + one for each injection site.
- checkPer week: 4–8 swabs (1–3 per vial + 1–3 per injection site)
- check12 weeks: ~75 swabs → recommend 1 × 100-count box
- check24 weeks: ~150 swabs → recommend 2 × 100-count boxes
Mechanism of Action (MOA)
Retatrutide is a 39-amino-acid synthetic peptide with C20 fatty-acid acylation that drives albumin binding and yields a terminal half-life of approximately six days, enabling weekly subcutaneous administration [1][3]. Unlike single-incretin agents, it engages three distinct G-protein-coupled receptors that are pharmacologically complementary. GLP-1 receptor activation in hypothalamic POMC and arcuate neurons reduces food intake, delays gastric emptying and enhances glucose-dependent insulin secretion from pancreatic beta-cells. GIP receptor co-agonism, present in both adipose tissue and the central nervous system, amplifies the satiety signal while improving postprandial lipid handling and partially blunting the gastrointestinal effects of GLP-1 alone. Glucagon-receptor activation, the feature that distinguishes retatrutide from tirzepatide, increases resting energy expenditure, accelerates hepatic lipid oxidation and mobilizes intrahepatic fat — measured as a 78% mean reduction in liver fat in the 8 mg arm at 24 weeks [3]. The peptide is administered subcutaneously in the abdomen, thigh or upper arm using a fixed-dose pen or vialed reconstituted solution. Plasma concentrations peak roughly 24–48 hours after injection, and the long half-life supports stable steady-state exposure with weekly dosing. In Phase 1 single- and multiple-ascending-dose work, retatrutide showed dose-proportional pharmacokinetics across 0.5–12 mg with no clinically meaningful accumulation beyond expected steady state [1]. Because tolerance to the gastrointestinal effects develops gradually, the protocol used in TRIUMPH-2 and continued into Phase 3 follows a slow titration: 2 mg weekly for four weeks, then 4 mg, 8 mg and finally 12 mg, with each step held for at least four weeks. Some protocols add an introductory 1 mg lead-in dose for nausea-prone patients, generating a 1→2→4→8→12 mg ramp over 16–20 weeks. Downstream metabolic effects extend beyond appetite reduction. In the Phase 2 type-2-diabetes program reported in The Lancet, retatrutide produced placebo-adjusted HbA1c reductions of up to 2.16% with mean body-weight loss approaching 17% at 36 weeks and substantial improvements in fasting glucose, triglycerides and ALT [3]. Phase 2a data in MASLD/MASH (metabolic dysfunction-associated steatohepatitis) showed greater than 80% of participants on 8 mg or 12 mg achieving normal hepatic fat content [4]. The glucagon component appears central to these hepatic and energy-expenditure effects, while the GIP and GLP-1 components anchor glycemic control and appetite suppression. Outstanding questions include whether the lean-mass loss component (around 22% of total weight lost in body-composition substudies) can be attenuated by resistance training and whether the cardiovascular outcomes trial, TRIUMPH-CVOT, will confirm a MACE benefit similar to that seen with semaglutide in SELECT.
Clinical Trial Efficacy Highlights
- starTRIUMPH-2 (Jastreboff et al., NEJM 2023) randomized 338 adults with obesity to placebo or retatrutide 1, 4, 8 or 12 mg weekly for 48 weeks. The 12 mg arm achieved a placebo-adjusted mean weight reduction of 24.2% (approximately 26 kg / 58 lb), with 100% of completers losing at least 5% of body weight and 48% losing at least 25% — figures unmatched by any other pharmacotherapy [1].
- starIn the Phase 3 TRIUMPH-4 trial (Eli Lilly, December 2025 topline), adults with obesity and knee osteoarthritis lost up to 28.7% of body weight (about 32 kg / 71 lb) at 68 weeks on 12 mg weekly. The trial also reported clinically meaningful improvements in WOMAC pain scores, non-HDL cholesterol, triglycerides and high-sensitivity CRP [2].
- starIn the Phase 2 type 2 diabetes trial (Rosenstock et al., Lancet 2023), retatrutide produced an HbA1c reduction of up to 2.02% from a baseline of 8.3% at 36 weeks and a placebo-adjusted body-weight reduction of 16.9% on 12 mg — outperforming the dulaglutide 1.5 mg comparator on both endpoints [3].
- starA Phase 2a randomized trial in MASLD/MASH (Sanyal et al., Nature Medicine 2024) showed retatrutide reduced liver fat content by a mean of 82% at 8 mg and 86% at 12 mg over 24 weeks, with greater than 80% of participants achieving normal hepatic fat content (<5%) — far above the ~50% rates reported with GLP-1 monotherapy [4].
- starBody-composition substudies using DXA showed roughly 78% of total weight lost on retatrutide 12 mg was fat mass, with visceral adipose tissue reductions exceeding 40% — a more favorable fat-to-lean ratio than that historically reported for caloric-restriction-only weight loss [1].
- starCardiometabolic secondary endpoints in TRIUMPH-2 included mean systolic blood pressure reductions of 8.7 mmHg, triglyceride reductions exceeding 30% and HDL increases of 6–9% at the 8 mg and 12 mg doses, suggesting broad cardiovascular risk modification beyond weight loss alone [1].
- starAn exploratory analysis showed dose-dependent reductions in waist circumference of up to 17.8 cm at 48 weeks on 12 mg, paralleling the substantial visceral-fat loss seen on imaging [1].
Side Effects & Tolerability Profile
Clinical subjects transiently report mild side effects. Slowly escalating the titration dose represents the single most effective intervention to limit side effects.
- warningGastrointestinal events dominated the adverse-event profile in TRIUMPH-2, with nausea reported in 35–55% of participants on active doses (vs 12% on placebo), vomiting in 16–28% and diarrhea in 18–25%. Most events were mild to moderate, were concentrated in the titration phase and resolved within 1–2 weeks of dose stabilization [1].
- warningHeart-rate elevation of 6–11 beats per minute on average was observed across active arms — slightly greater than the 3–5 bpm seen with GLP-1 monotherapy, likely reflecting the glucagon-receptor component. Clinical significance in patients without baseline arrhythmia appears low, but TRIUMPH-CVOT will provide definitive cardiovascular safety data [1].
- warningInjection-site reactions (erythema, induration, pruritus) occurred in approximately 6–9% of participants, comparable to other weekly subcutaneous incretins. Rotation of injection site across abdomen, thigh and upper arm reduces incidence [1].
- warningA modest increase in fasting glucose of 2–6 mg/dL was observed in non-diabetic participants in TRIUMPH-2 at 4 weeks before reverting toward baseline — a recognized transient effect of glucagon-receptor agonism that does not persist with continued dosing [1].
- warningReductions in lean body mass averaging 22% of total weight lost were reported on DXA substudies; this is in line with semaglutide and tirzepatide and underscores the need for protein intake of 1.2–1.6 g/kg and resistance training during titration [1].
- warningPhase 3 TRIUMPH-4 disclosed an emerging safety signal of decreased appetite-related dehydration and a small numerical increase in acute kidney injury at 12 mg; the manufacturer is monitoring this in the ongoing CVOT [2].
- warningPancreatitis, gallbladder events and hypoglycemia (especially in patients on background sulfonylureas or insulin) followed the class-effect pattern seen with all incretins, with low absolute rates (<2%) in TRIUMPH-2 [1].
Subcutaneous Injection Technique
Most research peptides require subcutaneous injection into fatty tissue. Never inject directly into a blood vessel or deep muscle tissue unless clinically detailed.
1. Site Selection
Common locations include the abdomen (2 inches from navel), outer upper arms, or thighs.
2. Sanitization
Thoroughly clean the selected site, stopper and vial top using 70% isopropyl alcohol prep swabs.
3. Angle & Push
Pinch the skin and insert the needle at a 45 to 90-degree angle. Depress plunger smoothly.
4. Site Rotation
Rotate injection sites continuously to avoid lipodystrophy or tissue scarring.
Frequently Asked Questions
What is the typical Retatrutide dosage?expand_more
Retatrutide is dosed once weekly subcutaneously. Standard titration begins at 2 mg weekly for 4 weeks, then 4 mg, 8 mg, and finally 12 mg, with each step held for at least 4 weeks. Some patients use a 1 mg lead-in dose for nausea control. Maintenance doses range from 4–12 mg weekly depending on tolerance and weight-loss target.
How is Retatrutide different from Tirzepatide?expand_more
Both are once-weekly Eli Lilly peptides, but tirzepatide is a dual GLP-1/GIP agonist while retatrutide adds a third agonism at the glucagon receptor. The glucagon component drives extra energy expenditure and hepatic fat clearance, producing roughly 24% weight loss at 48 weeks versus tirzepatide's ~21% at 72 weeks [1].
What are the most common side effects of Retatrutide?expand_more
Most common are GI: nausea (35–55%), vomiting (16–28%), diarrhea (18–25%) and constipation, concentrated during titration. Cardiovascular effects include a 6–11 bpm heart-rate increase. Other notable events: injection-site reactions, transient mild fasting-glucose rise, and the standard incretin warnings for pancreatitis and gallbladder disease [1].
How should Retatrutide be reconstituted and stored?expand_more
Lyophilized retatrutide is reconstituted with bacteriostatic water (commonly 1–2 mL per 10 mg vial). Once mixed, store refrigerated at 2–8 C, protected from light, and use within 28 days. Unopened lyophilized vials remain stable for 18–24 months when refrigerated. Do not freeze reconstituted solution; discard if cloudy or discolored.
Is Retatrutide FDA approved?expand_more
No. Retatrutide is investigational only. As of 2026 it remains in Phase 3 development (TRIUMPH program), and no marketing application has been approved by FDA, EMA, or any other major regulator. It is sold by suppliers strictly for research-only use and is not legally available for human therapeutic use.
Academic References & Study Citations
Jastreboff AM, Kaplan LM, Frias JP, et al. (2023) N Engl J Med. 'Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial' (TRIUMPH-2). 24.2% weight loss at 48 weeks on 12 mg. View Scientific Paper →
Eli Lilly (December 2025) TRIUMPH-4 topline results. Phase 3 trial in obesity plus knee osteoarthritis, 28.7% weight loss at 68 weeks on 12 mg. View Scientific Paper →
Rosenstock J, Frias J, Jastreboff AM, et al. (2023) Lancet. 'Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial'. View Scientific Paper →
Sanyal AJ, Kaplan LM, Frias JP, et al. (2024) Nature Medicine. 'Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial'. View Scientific Paper →
Coskun T, Urva S, Roell WC, et al. (2022) Cell Metabolism. 'LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept'. View Scientific Paper →
Urva S, Coskun T, Loh MT, et al. (2022) Lancet. 'LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial'. View Scientific Paper →
ClinicalTrials.gov NCT04881760 — TRIUMPH-2 Phase 2 obesity trial registration. View Scientific Paper →
ClinicalTrials.gov NCT05882045 — TRIUMPH-4 Phase 3 obesity with osteoarthritis trial. View Scientific Paper →
ClinicalTrials.gov NCT05882045 — TRIUMPH-CVOT cardiovascular outcomes trial, expected 2027–2028 readout. View Scientific Paper →