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Retatrutide (LY3437943)
An investigational once-weekly injectable peptide that activates THREE receptors at once — GIP, GLP-1 and glucagon. Honest framing: in a 48-week phase-2 obesity trial it produced the largest mean weight loss yet reported for an incretin-class drug (about -24% at the top dose), and it cut liver fat dramatically in a MASLD substudy. BUT it is NOT APPROVED anywhere — the first phase-3 trial (a type-2-diabetes trial, TRANSCEND-T2D-1) has now reported but the phase-3 obesity and cardio-kidney-outcome (TRIUMPH) program is still ongoing as of 2026, so long-term safety and hard outcomes are unknown. It is a prescription-pathway drug, not a dietary supplement, and the 'retatrutide' sold grey-market online despite no approval is especially risky.
Prescription medication — not a dietary supplement
Retatrutide is a prescription (or investigational) drug, not a supplement. It is included here for reference because people research and discuss it (often used off-label) — not as a recommendation. Take it only under a qualified clinician's supervision and only as prescribed; do not source it from grey-market vendors, where identity, purity, and dosing are unverified. The evidence below reflects its clinical trials.
What the evidence says
Most Retatrutide studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 2022–2026 with a typical study size of 15,584 participants.
Based on 28 studies · 8 meta-analyses · 8 RCTs · 169,791 total participants
Confidence
High confidenceBy outcome
Scored Moderate (5.5) because phase-2 trials and one phase-3 type-2-diabetes RCT show striking, consistent weight and glycemic effects, but it remains an investigational, unapproved drug with no obesity-population phase-3 or cardiovascular-outcome data.
27 rigorous studies
7 randomized trials · 14 meta-analyses · 17 systematic reviews
Our evidence rating for Retatrutide is accountable to this entire body of rigorous research indexed in PubMed — not a hand-picked subset.
PubMed · as of Jul 2026
11 trials ongoing or recruiting · 21 completed on ClinicalTrials.gov
2 of the completed trials have posted results
Registered trials show research momentum for Retatrutide, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Aug 2026
Retatrutide (developmental code LY3437943) is a single synthetic peptide engineered by Eli Lilly to be a balanced triple agonist of three entero-pancreatic hormone receptors: the glucose-dependent insulinotropic polypeptide receptor (GIPR), the glucagon-like peptide-1 receptor (GLP-1R), and the glucagon receptor (GCGR).
The rationale is mechanistic stacking: GLP-1 and GIP agonism reduce appetite/food intake and improve insulin secretion (the same axis exploited by semaglutide and tirzepatide), while adding glucagon-receptor agonism is intended to increase energy expenditure and drive hepatic fat mobilisation — components the GLP-1/GIP drugs lack.
Protraction chemistry gives it a ~6-day half-life suitable for once-weekly subcutaneous dosing. The human evidence to date is genuinely striking but still early.
A phase-1b multiple-ascending-dose study in type 2 diabetes and a phase-2 type 2 diabetes trial showed dose-dependent HbA1c and weight reductions (top doses outperforming dulaglutide).
The headline result is the 48-week phase-2 obesity trial (NEJM 2023, n=338), where the 12 mg dose produced a least-squares mean weight loss of about 24.2% at 48 weeks — the largest reported for an incretin-class agent and approaching surgical-range loss.
A phase-2a substudy in metabolic dysfunction-associated steatotic liver disease (MASLD) showed liver-fat reductions of roughly -81% to -82% at the 8 and 12 mg doses, with most participants reaching normal liver fat. The honest caveats are substantial.
The headline efficacy (the ~24% obesity weight loss and the MASLD liver-fat data) is still PHASE-2: the first phase-3 trial to report (TRANSCEND-T2D-1, Lancet 2026, n=537) was a 40-week type-2-diabetes monotherapy study that confirmed the glycemic/weight signal (HbA1c -1.94%, weight -15.3% at 12 mg vs placebo), but the phase-3 obesity program and the cardio-kidney-outcome trial (TRIUMPH-Outcomes) are still ongoing, so there are still NO cardiovascular/renal/mortality outcome data and no phase-3 obesity-population confirmation of the ~24% figure as of 2026.
Retatrutide is INVESTIGATIONAL and approved nowhere — it is not a dietary supplement and not yet an approved medicine.
Adverse effects are class-typical (dose-related gastrointestinal events) plus glucagon-agonism-specific signals: dose-dependent increases in heart rate were seen, and glucagon agonism can transiently raise glucose, so the net metabolic effect depends on receptor balance.
Like the whole GLP-1 class it carries expected concerns about gallbladder events, pancreatitis, lean-mass loss alongside fat loss, and a class thyroid C-cell warning.
Crucially, despite no approval, unregulated 'retatrutide' is already being sold grey-market online; using an unapproved investigational drug with no clinical oversight, no identity/purity guarantee and no safety monitoring is especially dangerous.
Because it is a prescription-pathway investigational drug rather than a supplement to recommend, it is sandboxed out of goal-based and stack recommendations here.
Like the approved incretin drugs, retatrutide activates the GLP-1 and GIP receptors, which reduce appetite and food intake, slow gastric emptying, and enhance glucose-dependent insulin secretion. This is the shared backbone of the incretin class and drives much of the glycemic and weight effect.
The distinguishing third arm: adding glucagon-receptor agonism is intended to raise energy expenditure and mobilise hepatic fat. Preclinical work attributes the augmented weight loss specifically to this glucagon component layered on top of GLP-1/GIP-driven calorie-intake reduction — but glucagon agonism can also transiently raise glucose and heart rate.
Retatrutide was tuned to an empirically optimised receptor potency ratio across GCGR, GIPR and GLP-1R (in vitro it shows balanced glucagon/GLP-1 activity with relatively more GIP activity). The clinical effect therefore depends on the net balance of three signals, not a single target — a key uncertainty that phase-3 trials are meant to resolve.
How Retatrutide works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
There is no approved use; obtaining or using grey-market 'retatrutide' means taking an unapproved investigational drug with no clinical oversight, dosing standard, or product-quality guarantee. Strongly discouraged.
High hypoglycemia risk if combined; only relevant under trial-level medical supervision with secretagogue adjustment.
The dose-dependent heart-rate increase and absence of cardiovascular-outcome data make unsupervised use particularly unwise.
Contraindicated — not studied; weight-loss pharmacotherapy is avoided in pregnancy.
Incretin-class agonism slows gastric emptying, which can reduce the rate/extent of absorption of co-administered oral drugs — relevant for time-critical or narrow-therapeutic-index oral medicines.
Combining a glucose-lowering incretin agonist with insulin or sulfonylureas increases hypoglycemia risk; dose reduction of the secretagogue is typically required in supervised use.
Stacking retatrutide with another GLP-1/GIP incretin agonist compounds gastrointestinal toxicity and glucose-lowering with no evidence of benefit; this combination is not studied and is dangerous.
Tip: Dose-related; mitigated by a lower starting dose and slow escalation. Most cases mild-to-moderate.
Tip: Class-typical GI effects; generally transient and dose-related.
Tip: Dose-dependent rise peaking ~24 weeks then declining; long-term cardiovascular significance unknown. Requires clinical monitoring.
Tip: Marked appetite suppression; as with the GLP-1 class, part of the weight lost is lean mass — adequate protein and resistance exercise are advised in supervised settings.
Tip: Rapid weight loss and incretin-class effects are associated with gallbladder events; report severe abdominal pain.
Tip: A class concern for incretin drugs; discontinue and seek care for persistent severe abdominal pain. Long-term incidence unknown without phase-3 data.
Retatrutide has an evidence score of 5.5/10 — moderate evidence based on 24 indexed studies. An investigational once-weekly injectable peptide that activates THREE receptors at once — GIP, GLP-1 and glucagon. Honest framing: in a 48-week phase-2 obesity trial it produced the largest mean weight loss yet reported for an incretin-class drug (about -24% at the top dose), and it cut liver fat dramatically in a MASLD substudy. BUT it is NOT APPROVED anywhere — the first phase-3 trial (a type-2-diabetes trial, TRANSCEND-T2D-1) has now reported but the phase-3 obesity and cardio-kidney-outcome (TRIUMPH) program is still ongoing as of 2026, so long-term safety and hard outcomes are unknown. It is a prescription-pathway drug, not a dietary supplement, and the 'retatrutide' sold grey-market online despite no approval is especially risky. Representative study: PMID 42250575.
The commonly studied dose of Retatrutide is Investigational — NO approved dose. Phase-2 trials used once-weekly subcutaneous injection with stepwise escalation (e.g. start 2 mg) up to 8-12 mg maintenance. There is no approved regimen; do not self-dose an unapproved drug.. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
Timing is flexible for Retatrutide — consistent daily use matters more than the time of day. Trials dosed once weekly subcutaneously with gradual dose escalation to limit gastrointestinal effects; the ~6-day half-life supports once-weekly administration.
Retatrutide should be used with caution — talk to a healthcare provider before taking it. The most commonly reported side effects are nausea / vomiting, diarrhoea / constipation, increased heart rate. Use caution if any of these apply to you: Not a dietary supplement and not an approved drug — investigational; do not self-source grey-market vials; Personal/family history of medullary thyroid carcinoma or MEN 2 (expected GLP-1-class thyroid C-cell warning); History of pancreatitis.
Semaglutide
Mostly mechanism / observationalAn FDA-approved GLP-1 receptor agonist (Ozempic/Rybelsus for type 2 diabetes, Wegovy for chronic weight management) with genuinely strong, large-RCT evidence for glycemic control and substantial weight loss, plus a cardiovascular-outcomes benefit. Honest appraisal: this is a real prescription medicine with real efficacy AND real risks — a boxed warning for thyroid C-cell tumors, pancreatitis and gallbladder risk, very common GI side effects, and growing concern about grey-market/compounded versions. It is included here for reference only, not as a supplement and not auto-recommended.
Tirzepatide
Mostly mechanism / observationalAn FDA-approved prescription medication (Mounjaro for type 2 diabetes, Zepbound for obesity and obstructive sleep apnea), not a dietary supplement. Honest appraisal: in head-to-head phase-3 trials it is the most effective approved weight-loss drug to date — up to ~21% body-weight loss over 72 weeks and superior to semaglutide — but it is a real medicine with real risks: a boxed warning for thyroid C-cell tumors, common GI side effects, and pancreatitis/gallbladder signals. Do not source or use it outside a prescription.
Liraglutide
Mostly mechanism / observationalAn FDA-approved, once-daily GLP-1 receptor agonist (Victoza for type 2 diabetes, Saxenda for chronic weight management). Honest appraisal: a real prescription medicine with genuinely strong large-RCT evidence for glycemic control and moderate weight loss, plus a cardiovascular-outcomes benefit (LEADER). It also carries real risks — a boxed warning for thyroid C-cell tumors, pancreatitis and gallbladder risk, very common GI side effects, and lean-mass loss with weight loss. Included here for reference only; it is NOT a supplement and is not auto-recommended.
Orforglipron
Mostly mechanism / observationalAn investigational ORAL, non-peptide small-molecule GLP-1 receptor agonist for obesity and type 2 diabetes — the headline is the convenience of a once-daily pill (no injection, no cold chain, no food/water restrictions) delivering GLP-1-class glycemic and weight benefit. Honest appraisal: the phase-2 data are strong and the first phase-3 read-outs (ATTAIN/ACHIEVE) are promising, but it is INVESTIGATIONAL and not yet approved as a general weight-loss medicine, has the full GLP-1-class side-effect burden (very common dose-dependent nausea/vomiting/diarrhea, higher discontinuation than injectables in some comparisons), and the expected thyroid C-cell class warning and long-term outcomes are unsettled. It is NOT a dietary supplement; listed here for reference only.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 28 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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