Retatrutide
An investigational once-weekly triple GLP-1/GIP/glucagon receptor agonist that has produced the deepest weight-loss numbers ever recorded in obesity trials.
Retatrutide (LY3437943) is a 39-amino-acid synthetic peptide developed by Eli Lilly that simultaneously activates the GLP-1, GIP, and glucagon receptors — adding glucagon-driven energy expenditure and hepatic fat oxidation on top of the appetite-suppressing, insulin-sensitizing effects that make semaglutide and tirzepatide work. A Phase 2 NEJM trial showed up to 24.2% body-weight loss at 48 weeks, and the pivotal Phase 3 TRIUMPH-1 obesity trial reported roughly 28% mean loss at 80 weeks, rising to about 30% at two years. It is not FDA-approved and remains in Phase 3 registrational development as a research-use-only compound.
Class
Synthetic 39-amino-acid triple hormone receptor agonist (GLP-1/GIP/glucagon)
Half-life
~6 days (once-weekly dosing; steady state at ~4 weeks)
Routes
Subcutaneous injection
Category
Weight Loss & Metabolic
Researched benefits
What it's studied for
Record-setting weight loss
Phase 2 data showed up to 24.2% mean body-weight reduction at 48 weeks (12 mg), and Phase 3 TRIUMPH-1 reported ~28% at 80 weeks rising to ~30% (about 85 lb) at 104 weeks — the deepest obesity-drug numbers published to date, exceeding semaglutide (~15%) and tirzepatide (~21-22%) at comparable timepoints.
Powerful appetite suppression
The GLP-1 and GIP arms act on hypothalamic appetite-regulating neurons and slow gastric emptying, producing strong satiety and reduced 'food noise'; community reports describe sharper food aversion and faster onset than tirzepatide.
Increased energy expenditure
The glucagon-receptor component raises resting energy expenditure by roughly 3-6% and drives direct lipolysis and thermogenesis — an intake-plus-expenditure mechanism unavailable to single or dual agonists.
Hepatic fat reduction
Glucagon-stimulated hepatic fatty acid oxidation drove up to ~86% relative reduction in liver fat in Phase 2, positioning retatrutide as a candidate MASH/NAFLD therapy under Phase 3 evaluation.
Glycemic control
GLP-1 and GIP agonism enhance glucose-dependent insulin secretion, delivering HbA1c reductions comparable to tirzepatide in type 2 diabetes populations.
Cardiometabolic improvements
Phase 2 data showed blood pressure reduction (~11/5 mmHg) and triglyceride reduction (~30%), with a systematic review and meta-analysis examining effects on blood pressure and lipids as secondary benefits beyond weight loss.
Mechanism
How it works
Retatrutide is a balanced triple agonist: its relative potencies at the GLP-1 receptor (GLP-1R), GIP receptor (GIPR), and glucagon receptor (GCGR) are within one order of magnitude of each other. It carries a C20 fatty diacid side chain (similar to semaglutide) that binds albumin and extends the plasma half-life to about 6 days, enabling once-weekly subcutaneous dosing with steady state reached at roughly 4 weeks.
The GLP-1 arm activates receptors on pancreatic beta cells to drive glucose-dependent insulin secretion, on hypothalamic POMC/NPY/AgRP neurons to suppress appetite, and slows gastric emptying to prolong satiety — the same mechanism as semaglutide. The GIP arm adds enhanced glucose-dependent insulin secretion and modulates adipose lipid metabolism, the 'twincretin' combination shared with tirzepatide.
The glucagon-receptor arm is retatrutide's signature. GCGR activation on hepatocytes stimulates hepatic fatty acid oxidation and reduces hepatic lipid accumulation (the likely basis for its strong liver-fat effects), while activation on adipose tissue enhances lipolysis and raises resting metabolic rate by roughly 3-6%. Additional appetite-suppressive signaling occurs in the hypothalamus, and brown adipose tissue activation is under investigation as a secondary contributor to energy expenditure.
By attacking weight from both intake (appetite suppression via GLP-1/GIP) and expenditure (glucagon-driven thermogenesis and lipolysis), retatrutide produces deeper weight loss than dual agonists. The glucagon component is also responsible for its distinct safety profile — a mean heart-rate rise of roughly 6-8 bpm and transient elevations in fasting glucose during uptitration as hepatic glucose output rises.
Dosing protocols
Dosing & administration
Dosing reflects protocols reported in research and community literature for educational purposes. It is not medical advice or a recommendation. Most peptides here are not approved for human use.
Reconstitution
Much research-grade retatrutide is supplied as a pre-concentrated clear 5 mg/mL or 10 mg/mL solution in a multi-use vial requiring no reconstitution — just inspect (clear and colorless; discard if cloudy or with particulates) and draw. If supplied as lyophilized powder, a standard reconstitution is 10 mg powder + 1 mL bacteriostatic water = 10 mg/mL (use 2 mL for 5 mg/mL). Inject BAC water down the vial wall, swirl gently (do not shake), and allow 2-5 minutes to fully dissolve. Store refrigerated at 2-8°C, use within 30-60 days, do not freeze. At 5 mg/mL: 2 mg = 0.4 mL, 4 mg = 0.8 mL, 8 mg = 1.6 mL, 12 mg = 2.4 mL (8-12 mg require a 3 mL syringe).
Beginner (uptitration)
- Dose
- 2 mg escalating stepwise toward 4-8 mg
- Frequency
- Once weekly
- Timing
- Same day each week; time of day not critical, many prefer evening to sleep through initial nausea
- Duration
- Weeks 1-20 (2 mg wk 1-4, 4 mg wk 5-8, 4-8 mg wk 9-12, 8 mg wk 13-16, 8-12 mg wk 17-20)
- Route
- Subcutaneous (abdomen, 2+ inches from navel, rotating sites)
Matches the Phase 2 trial schedule to establish tolerance. Hold at the current dose 1-2 extra weeks if GI tolerance is borderline; do not skip titration steps. Many users see substantial loss at 8 mg and do not escalate further.
Intermediate (maintenance)
- Dose
- 8-12 mg (most settle at 8 mg)
- Frequency
- Once weekly
- Timing
- Same day each week
- Duration
- Weeks 20-52 and ongoing (chronic therapy)
- Route
- Subcutaneous
8 mg captures roughly 75-80% of the weight loss with 60-70% of the side effects; 12 mg is reserved for stronger weight-loss goals or T2DM/NAFLD indications. Designed as chronic therapy — cycling typically causes rapid weight regain.
Advanced (indication-specific)
- Dose
- 8-12 mg (titrate to max tolerated)
- Frequency
- Once weekly
- Timing
- Same day each week
- Duration
- 48 weeks minimum for NAFLD/MASH; ongoing for T2DM or cardiovascular risk reduction
- Route
- Subcutaneous
For NAFLD/MASH, imaging-confirmed candidates use 8-12 mg with monthly ALT/AST and quarterly MRI-PDFF or FibroScan. For T2DM, 8 mg is often sufficient; withdraw or reduce sulfonylureas and insulin to prevent hypoglycemia. Requires full lab monitoring.
- Typical range is 1,000-12,000 mcg (1-12 mg) per week; the 12 mg maximum yields the greatest weight loss and the greatest side-effect burden.
- Not weight-based — dosing follows a fixed clinical-trial escalation schedule.
- Baseline and periodic monitoring recommended: HbA1c, fasting glucose, lipid panel, CMP/liver function, thyroid, resting heart rate, weight and blood pressure; recheck at weeks 4, 12, 20 and every 12 weeks on maintenance.
- Do not proceed to the next titration step if nausea/vomiting is limiting intake, heart rate rises >20 bpm from baseline, fasting glucose exceeds ~130 mg/dL without other cause, or there are signs of pancreatitis.
- Missed dose: if less than 3 days late, take as soon as remembered; if more than 3 days late, skip and resume at the usual time — do not double-dose.
- Uptitrate more slowly in adults over 75; use caution in hepatic impairment (retatrutide is predominantly hepatically cleared); mild-to-moderate renal impairment does not require adjustment.
- Because it is not FDA-approved, verify research-grade material via HPLC purity (ideally >=98%) and mass-spec confirmation of the ~4731 Da mass with a batch Certificate of Analysis.
Evidence
Research & clinical studies (10)
Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial
In a 48-week Phase 2 trial (n=338), retatrutide 12 mg reduced mean body weight by 24.2% versus 2.1% for placebo, among the largest reductions reported for any pharmacological agent.
PMID 37366315Design of the TRIUMPH phase 3 clinical trial programme for retatrutide in obesity and cardiometabolic disease
Describes the TRIUMPH Phase 3 program evaluating retatrutide across more than 5,800 participants, including cardiovascular, kidney, and MASH endpoints.
PMID 41090431Metabolic Dysfunction-Associated Steatotic Liver Disease and Incretin Receptor Agonists: A Metabolic Approach to Halting Liver Disease Progression
Retatrutide shows early clinical promise for MASLD through hepatoprotective and metabolic effects, though evidence on fibrosis progression remains limited.
PMID 42195239Retatrutide And Lipid And Metabolite Profiles In Participants With Obesity With Or Without Type 2 Diabetes
Retatrutide altered metabolites tied to fatty acid oxidation and insulin resistance, changes that mediated a substantial portion of weight reduction in participants with and without T2D.
PMID 42135195Effect of Retatrutide, a Novel Triple Receptor Agonist, on Blood Pressure and Lipid Levels: A Systematic Review and Meta-analysis of Randomized Controlled Trials
Pooled RCT evidence examined retatrutide's effects on blood pressure and lipid levels as cardiometabolic outcomes beyond weight loss.
PMID 42371360Beyond weight loss: multisystem benefits of obesity medications
Emerging multiagonist obesity medications including retatrutide showed metabolic, cardiovascular, neuropsychiatric, and quality-of-life benefits via weight-mediated and direct receptor-mediated mechanisms.
PMID 42208956Dysesthesia associated with GLP-1 agonist therapies: data-mining analysis and literature review
Pharmacovigilance data strengthened evidence for dysesthesia (abnormal, often burning skin sensations) seen in trials of semaglutide, tirzepatide, and retatrutide.
PMID 42168638Diabetes Mellitus and Stroke: Pathophysiological Connections and Therapeutic Potential of GLP-1 and GLP-1/GIP Receptor Agonists
GLP-1 and dual/multi-agonists including retatrutide show potential to reduce stroke risk in diabetes, though larger long-term trials are needed.
PMID 42198313Retatrutide: Triple acting jab for type 2 diabetes lowers blood sugar and boosts weight loss, trial reports
Trial reporting indicated retatrutide lowered blood sugar and increased weight loss in type 2 diabetes.
PMID 42264536Benefits and Harms of Pharmacologic Treatments in Adults With Overweight or Obesity: A Living Systematic Review and Network Meta-analysis for the American College of Physicians
Network meta-analysis of anti-obesity pharmacotherapies contextualized retatrutide's benefits and harms against other agents.
PMID 42296503Combinations
Stacking & blends
Lean-mass preservation (body recomposition)
Preserve lean mass during the retatrutide-induced caloric deficit and reduce visceral fat
Growth-hormone secretagogues (Tesamorelin ~2 mg/day + Ipamorelin ~200 mcg, pre-bed) counter lean-mass loss and add VAT reduction; retatrutide's 6-day half-life makes GHS timing flexible. Paired with protein at ~1.0-1.2 g/lb, resistance training, and creatine.
T2DM glycemic optimization
Enhance glycemic control and buffer glycemic variability during dose changes
Metformin 500-1000 mg/day is a synergistic standard adjunct in type 2 diabetes; sulfonylureas and insulin should be reduced or withdrawn to prevent hypoglycemia during uptitration.
Cardiorenal add-on
Add cardiorenal protection in T2DM/high-risk patients
An SGLT2 inhibitor (empagliflozin 10-25 mg/day) is synergistic for cardiorenal benefit and can be added after retatrutide dose stabilization.
MK-677 lean-mass alternative (caution)
Oral GH secretagogue for lean-mass preservation
MK-677 supports lean mass but stimulates appetite while retatrutide suppresses it — opposing signals that net to moderated appetite; listed as a caution interaction.
Safety
Side effects & considerations
Commonly reported effects
Contraindications & cautions
- Personal or family history of medullary thyroid carcinoma (MTC)
- Multiple Endocrine Neoplasia syndrome type 2 (MEN-2)
- Personal history of acute pancreatitis
- Active gallbladder disease / acute cholecystitis
- Pregnancy or planning pregnancy
- Breastfeeding
- Active eating disorder
- Severe heart failure (NYHA III-IV)
- Resting tachycardia — investigate cause first
- Concurrent use of semaglutide, tirzepatide, or other GLP-1 agonists (overlapping GLP-1 activity)
- Active malignancy
A moderate-risk profile driven by GI events plus glucagon-specific effects (heart-rate elevation, transient hyperglycemia). Reta is NOT better tolerated than tirzepatide — TRIUMPH-1 reported an 11.3% adverse-event discontinuation rate at 12 mg versus 4.9% for placebo, and a dysesthesia signal that appears unique among the GLP-1 class. Do not stack with other GLP-1 agonists. Stop and seek evaluation for signs of pancreatitis, severe/persistent tachycardia or new arrhythmia, acute gallbladder symptoms, or severe dehydration.
FAQ
Retatrutide — common questions
What is retatrutide (LY3437943)?
An investigational triple hormone receptor agonist from Eli Lilly that simultaneously activates GLP-1, GIP, and glucagon receptors — the first drug to target all three metabolic pathways, delivered as a once-weekly subcutaneous injection.
How does it differ from tirzepatide and semaglutide?
Semaglutide targets GLP-1 only and tirzepatide targets GLP-1 + GIP (dual). Retatrutide adds a third receptor, glucagon, which uniquely drives hepatic energy expenditure, fat oxidation, and thermogenesis — mechanisms unavailable to single or dual agonists.
How much weight loss does it produce?
Phase 2 showed up to 24.2% mean body-weight reduction at 48 weeks (12 mg), with ~26% of participants losing at least 30% of body weight and up to ~86% liver-fat reduction. The pivotal Phase 3 TRIUMPH-1 trial reported roughly 28% at 80 weeks, rising to about 30% (around 85 lb) at 104 weeks.
What are the side effects?
Mostly gastrointestinal — nausea, vomiting, diarrhea, constipation, decreased appetite — plus glucagon-specific effects: heart-rate elevation (~6-8 bpm) and transient fasting-glucose rises during uptitration. A distinctive dysesthesia (tingling/burning in the extremities) affected about 12.5% at 12 mg. Slow titration reduces GI burden.
What is the typical dosing protocol?
Per the Phase 2 schedule: start at 2 mg weekly SC, then titrate through 4 mg and 8 mg toward a maximum of 12 mg over ~20-24 weeks. The ~6-day half-life supports once-weekly dosing; many users settle at 8 mg, which captures most of the effect with fewer side effects.
Is retatrutide FDA-approved?
No. It is in Phase 3 clinical trials (the TRIUMPH program) for obesity, type 2 diabetes, MASH/NAFLD, and related conditions. It is available only as a research compound; approval is not expected before roughly 2027-2028.
Can I stack it with semaglutide or tirzepatide?
No. Retatrutide already includes GLP-1 agonism, so combining it with semaglutide or tirzepatide would produce dangerous overlapping GLP-1 activity and is strongly contraindicated.
Why is research-grade retatrutide quality so variable?
Its narrower manufacturing base, higher price, and lack of an FDA-approved reference product create wider purity variance and stronger incentive for underdosing. Independent HPLC purity testing and mass-spec confirmation of the ~4731 Da mass are the only meaningful quality signals.
