Peptide Health Lab

Metabolic & GLP-1

Retatrutide

FOR RESEARCH PURPOSES ONLY

Also known as: LY3437943, Triple hormone receptor agonist

Regulatory status
Research only
Evidence grade
Human RCT evidence

Last reviewed August 2, 2026 · 14 sources

What retatrutide is and how it works

Retatrutide, developed under the code LY3437943, is a single synthetic peptide that activates three receptors: the glucose-dependent insulinotropic polypeptide receptor, the glucagon-like peptide-1 receptor, and the glucagon receptor.[2] The first two are the incretin receptors that the approved metabolic peptides act on. The third is the departure.

Glucagon is usually discussed as insulin's counter-regulatory partner, the hormone that raises blood glucose. Adding an agonist at its receptor to a glucose-lowering molecule looks contradictory until the energy-expenditure side is included: glucagon receptor agonism is proposed to increase energy expenditure and act on hepatic fat metabolism, while the incretin components handle glycemic control and appetite. A review of the field places retatrutide alongside survodutide as the molecules testing whether simultaneous glucagon and GLP-1 receptor activation is worth its added complexity.[8]

Two consequences of the design show up in the published data and are worth holding together. The liver-fat reductions reported in the steatotic liver disease substudy are larger than the class norm.[9] So is the heart-rate increase seen in the obesity trial.[2] Both plausibly trace to the same receptor, and neither has been settled by an outcome trial.

It is administered as a once-weekly subcutaneous injection in trials. It is not an approved drug anywhere.

What the research actually shows

Unusually for a compound with research-only status, the retatrutide literature is human and randomized. It is also early, and the distinction between "large effect in phase 2" and "established treatment" is the whole content of this page.

Weight. The phase 2 obesity trial randomized 338 adults across six retatrutide arms and placebo for 48 weeks. Mean weight change at 48 weeks was −8.7% at 1 mg, −17.1% in the combined 4 mg group, −22.8% in the combined 8 mg group, and −24.2% at 12 mg, versus −2.1% on placebo; at 12 mg, 93% of participants lost at least 10% and 83% lost at least 15%.[2] Those are the numbers driving the attention this compound receives, and they came from a dose-finding trial with roughly fifty people in some arms.

Glycemia. The phase 2 diabetes trial in 281 participants reported glycated hemoglobin reductions up to 2.02 percentage points at 24 weeks, exceeding both placebo and dulaglutide 1.5 mg, with weight reductions near 17% at 36 weeks in the higher-dose arms.[3] A 40-week phase 3 monotherapy trial in 537 people with type 2 diabetes inadequately controlled by diet and exercise subsequently reported reductions of 1.69 to 1.94 percentage points and weight reductions of 11.5% to 15.3% across 4, 9, and 12 mg arms.[14] That is the first published phase 3 result for the molecule.

Liver. A randomized phase 2a substudy in 98 participants with at least 10% liver fat reported mean relative liver-fat reductions of 42.9%, 57.0%, and 81.4% at 1, 4, and 8 mg by 24 weeks, with normal liver fat reached by between 27% and 86% of participants across doses and none on placebo.[9] These are imaging endpoints in a substudy, not biopsy-confirmed histology.

Body composition. A DXA substudy of the diabetes trial found greater total fat-mass reduction than placebo or dulaglutide, and the investigators concluded that the ratio of lean-mass loss to total weight loss resembled other obesity treatments.[11]

Where the evidence is weak

Phase 2 is not phase 3, and one phase 3 trial is not a programme. The headline weight numbers come from a dose-finding trial of 338 people. The single published phase 3 trial is a 40-week monotherapy study in type 2 diabetes, not a weight-management registrational trial.[14] The registrational obesity programme runs to four phase 3 trials enrolling more than 5,800 participants, with sleep-apnea and knee-osteoarthritis protocols nested inside the weight-management trials. It has a published design paper and no published results.[12]

There are no outcome data. Nothing published tells us whether the metabolic changes translate into fewer cardiovascular events, slower kidney decline, or longer life. A chronic kidney disease trial has published its rationale and baseline characteristics only.[13] For the approved incretins, outcome trials materially changed how the drugs are understood; retatrutide has not been through that filter.

The heart-rate signal is unresolved. Dose-dependent increases peaked at 24 weeks and then declined in phase 2.[2] Absent a cardiovascular outcome trial, that observation sits without context. It is also the finding most specific to this molecule's third receptor.

Nothing is known about stopping. No published trial has examined withdrawal. For the approved incretins, dedicated withdrawal trials showed substantial regain. Nobody has asked that question here in the published record.[8]

Single sponsor, overlapping investigators. Every published efficacy trial is funded by one company, and several share investigators and infrastructure. That does not make the results wrong; it does mean independent replication has not happened yet, and the phase 2 body-composition substudy shows how thin the completer numbers can be beneath a headline: 103 of 189.[11]

Duration. The longest published exposure is 48 weeks. Long-term safety in humans is unstudied, and the class-level rodent thyroid C-cell finding has never been resolved for humans.[1]

Most of the safety picture here is borrowed. Three of the safety entries on this page carry no retatrutide number at all: delayed gastric emptying and aspiration risk, gallbladder and biliary disease, and pancreatitis. They are class findings from GLP-1 receptor agonist populations, extrapolated to a molecule that shares two of those three receptors and adds a third.[6][4][5] Extrapolation is the honest description of what those entries are, and it cuts both ways: the class data may overstate what retatrutide does, or understate it, and no published trial resolves which. Pregnancy is the starkest version of the same gap. Every cited trial excluded it, and nothing published describes retatrutide exposure in a human pregnancy.[7]

A note on the evidence badge above. This library grades evidence with three values: human RCT, animal only, and anecdotal. None of them says "randomized, but phase 2, in one sponsor's programme, with no outcome trial." Retatrutide is graded on human randomized evidence because published human randomized trials exist for its headline claims, which is what that grade means here. It does not mean the evidence base is comparable to a compound with completed registrational programmes and cardiovascular and kidney outcome trials behind it.[12] Read the badge alongside the research-only status and this section, not on its own.

Legal and regulatory status

Retatrutide is not approved by the FDA, or by any other regulator, for any indication. It is an investigational compound in active clinical development. Everything published about it comes from sponsor-run trials using sponsor-manufactured product under trial monitoring, which is why every claim on this page is tied to a trial rather than to a label.[12]

There is therefore no approved manufacturer, no assigned indication, no labeled dose, no beyond-use date, and no regulated quality standard for anything sold or distributed under this name. Material labeled as retatrutide outside a clinical trial is not the product any of these trials studied, and no published result carries over to it.

Peptide Health Lab does not sell peptides, does not tell anyone how to obtain them, and takes no position on how unapproved material reaches anyone. What the regulatory status means for a reader is narrower and more useful: promising phase 2 data with an unfinished registrational programme is the definition of a compound whose risk-benefit profile is not yet known.[14] Athletes in tested sport should check the current year's prohibited list rather than any static page.

Questions to bring to a provider

The useful conversation here is comparative, because two molecules in the same family already have approvals, outcome trials, and labels:

  • What is the actual goal, and what do the approved options with completed outcome trials offer for it?[8]
  • Given that the published evidence is phase 2 plus one phase 3 monotherapy trial, what would have to be true for an investigational triple agonist to be worth considering over an approved option?[14]
  • Does any history of arrhythmia, heart failure, or uncontrolled hypertension change how the dose-dependent heart-rate finding should be read?[2]
  • Is there a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2?[1]
  • Is there a history of pancreatitis, gallbladder disease, gastroparesis, or significant reflux, and how should the class findings on biliary disease and pancreatitis be weighted for a molecule that has never been studied for either?[4][5]
  • Every cited trial excluded pregnancy, intended pregnancy, and breastfeeding, and there is no label to fall back on. Is any of the three in the picture?[7]
  • What should happen before any procedure requiring sedation, given the class findings on retained gastric content?[6]
  • How would lean mass, strength, and nutrition be monitored during weight loss of the magnitude reported in these trials?[10]
  • Is enrollment in an ongoing registrational trial a realistic route to supervised access, rather than anything unmonitored?[12]

A clinician who answers "the phase 3 results aren't published yet, so let's use what has been" is giving a defensible answer, not a conservative one.

Evidence by claim

Grades describe how strong the evidence is; the line under each grade describes what kind of studies it is. How we grade evidence.

Weight reduction in adults with obesity
Human RCT evidence human RCT

In a 48-week phase 2 trial of 338 adults, mean weight change was −8.7% (1 mg), −17.1% (4 mg), −22.8% (8 mg), and −24.2% (12 mg) versus −2.1% on placebo. A reduction of at least 15% occurred in 83% of the 12 mg group versus 2% on placebo. Phase 2: dose-finding, 338 people, one programme.

[2]

Glycemic control in type 2 diabetes
Human RCT evidence human RCT

The phase 2 diabetes trial reported glycated hemoglobin reductions up to 2.02 percentage points at 24 weeks versus 0.01 on placebo and 1.41 with dulaglutide 1.5 mg. A subsequent 40-week phase 3 monotherapy trial in 537 participants reported reductions of 1.69–1.94 percentage points versus placebo differences of 0.88–1.12 points.

[3] [14]

Liver fat in metabolic dysfunction-associated steatotic liver disease
Human RCT evidence human RCT

A randomized phase 2a substudy of 98 participants with at least 10% liver fat reported mean relative reductions in liver fat at 24 weeks of −42.9% (1 mg), −57.0% (4 mg), and −81.4% (8 mg), with normal liver fat reached by 27% to 86% of participants across doses versus 0% on placebo. Imaging endpoints in a substudy, not biopsy-confirmed histological outcomes.

[9]

Fat-mass reduction during weight loss
Human RCT evidence human RCT

Total fat mass by DXA was the prespecified primary endpoint of a randomized substudy inside the phase 2 diabetes trial. Least-squares mean change in total fat mass versus placebo was −10.7 percentage points (4 mg, pooled), −21.6 (8 mg, pooled), and −18.7 (12 mg). That is a randomized comparison against both placebo and dulaglutide. Only 103 of the 189 substudy participants completed treatment with both a baseline and a week-36 scan.

[11]

Lean-mass preservation relative to other obesity treatments
Anecdotal reports only human RCT · review

The substudy investigators concluded that the proportion of lean mass lost relative to total weight lost resembled other obesity treatments. That conclusion is a narrative comparison across separate trials with different populations, measurement timing, and completer rates. It is not a randomized head-to-head of lean-mass outcomes, and no such comparison has been published. Reported lean-mass loss varies widely across incretin therapies, and no trial in the class has used strength or physical function as a primary endpoint.

[11] [10]

Cardiovascular, kidney, or mortality outcomes
Anecdotal reports only review · human RCT

No completed outcome trial exists. A chronic kidney disease trial (TRANSCEND-CKD) has a published rationale and baseline-characteristics paper and no published results. The dose-dependent heart-rate increase seen in phase 2 has not been evaluated against hard endpoints in any published trial. The honest statement is that outcome evidence does not yet exist for this molecule.

[13] [2]

Obstructive sleep apnea and knee osteoarthritis
Anecdotal reports only review

The registrational TRIUMPH programme nests sleep-apnea and knee osteoarthritis protocols inside two weight-management basket trials, with apnea-hypopnea index and a pain subscale as their endpoints. That design is published; the results are not. No published trial supports either claim today.

[12]

Long-term safety and durability
Anecdotal reports only human RCT · review

No published trial has followed retatrutide beyond 48 weeks, and none has examined what happens when it is withdrawn. The semaglutide and tirzepatide withdrawal trials answered that question unambiguously for those molecules. Absence of a finding is not a finding of safety.

[14] [8]

FOR RESEARCH PURPOSES ONLY

Typical protocol range in the research

  • Phase 2 obesity trial (338 adults, 48 weeks, once-weekly subcutaneous injection), the trial that produced the widely quoted weight figures

    Maintenance doses of 1, 4, 8, or 12 mg weekly, with initial doses of 2 mg or 4 mg in the escalating arms [2]

  • Phase 2 type 2 diabetes trial (281 participants, 36 weeks), with placebo and a dulaglutide active comparator

    Maintenance doses of 0.5, 4, 8, or 12 mg weekly across several escalation schedules [3]

  • Phase 3 monotherapy trial in type 2 diabetes inadequately controlled by diet and exercise (TRANSCEND-T2D-1, 537 participants, 40 weeks)

    4 mg, 9 mg, or 12 mg once weekly [14]

Every one of these figures is a trial arm using sponsor-manufactured product under trial monitoring. No regulator has approved a dose, no label exists, and the trials themselves show why that matters: the escalation schedule, not just the maintenance dose, changed how well the compound was tolerated.

Ranges are what published research reports, not a recommendation. PHL does not prescribe, and nothing here is personalized to you.

Side effects & safety signals

  • Gastrointestinal adverse events (nausea, vomiting, diarrhea, constipation)

    The most common adverse events in every published trial, dose-related in each. In the phase 2 diabetes trial, mild-to-moderate gastrointestinal events were the dominant category; in the phase 3 monotherapy trial, discontinuations attributed to adverse events ran 2–5% versus 0% on placebo. · Mostly mild to moderate and concentrated during escalation. The phase 2 obesity trial found these events were partially mitigated by starting at 2 mg rather than 4 mg. That is a finding about escalation design, reported by the investigators, and not a schedule for anyone.

    [2] [3] [14]

  • Dose-dependent increase in heart rate

    Reported in the phase 2 obesity trial, where dose-dependent heart-rate increases peaked at 24 weeks and declined thereafter. · This is the signal that most distinguishes a glucagon-containing agonist from the GLP-1 and GIP/GLP-1 compounds, and no completed cardiovascular outcome trial exists to put it in context. Existing arrhythmia, heart failure, or uncontrolled hypertension is a reason to raise this with a clinician rather than reason past it.

    [2]

  • No established long-term human safety profile

    Not established · The longest published exposure is 48 weeks in a 338-person phase 2 trial and 40 weeks in a 537-person phase 3 monotherapy trial. The registrational programme designed to answer safety questions at scale runs to four phase 3 trials enrolling more than 5,800 participants. Its design paper is published; its results are not in the peer-reviewed literature. This is an absence of data, not a finding of safety.

    [14] [12]

  • Thyroid C-cell findings in rodents across the incretin class

    Observed in rats and, to a lesser degree, mice; not observed in cynomolgus monkeys at more than 60 times human exposure levels. · GLP-1 receptor agonists stimulated calcitonin release and C-cell hyperplasia in rodents, while primates showed low thyroid C-cell receptor expression and no equivalent response; the authors state the long-term consequences in the human thyroid remain unknown. This is the class finding behind the medullary thyroid carcinoma and multiple endocrine neoplasia type 2 cautions applied to approved incretin drugs, and a personal or family history of either is a reason to raise the question with a clinician before considering anything in this class.

    [1]

  • Delayed gastric emptying and retained stomach contents before procedures (a class finding, not a retatrutide finding)

    Not measured for retatrutide. In a meta-analysis of 39 studies covering 1,253,498 subjects undergoing endoscopy, patients taking GLP-1 receptor agonists had higher odds of residual gastric content (odds ratio 4.86, 95% confidence interval 3.85 to 6.14) and of pulmonary aspiration (odds ratio 2.29, 1.36 to 3.87). · Slowed gastric emptying is a shared property of the receptor family retatrutide activates, and retained stomach contents raise aspiration risk under sedation. This is a class finding across GLP-1 receptor agonists, not a retatrutide finding: no published retatrutide trial has measured gastric emptying against a procedural endpoint. Any planned surgery, endoscopy, or sedated procedure is a reason to raise incretin exposure with the clinician arranging it and with the proceduralist, well in advance.

    [6]

  • Gallbladder and biliary disease (a class finding, not a retatrutide finding)

    Not established for retatrutide. A meta-analysis of 76 randomized trials and 103,371 patients reported a relative risk of 1.37 (95% confidence interval 1.23 to 1.52) for gallbladder or biliary disease with GLP-1 receptor agonists overall, and 2.29 (1.64 to 3.18) across the 13 trials conducted for weight loss. · In that analysis, risk was higher at higher doses and with longer treatment. Those are the two conditions the retatrutide weight data describe. Cholecystitis and cholelithiasis can require surgery. No published retatrutide trial has been powered for biliary events, so the class result is the only evidence that speaks to this at all, and a history of gallstones or biliary disease is a reason to raise the question with a clinician.

    [4]

  • Pancreatitis (a class signal, not a retatrutide finding)

    Not established for retatrutide. A retrospective cohort study in a health-claims database compared people prescribed GLP-1 receptor agonists for weight loss against people prescribed bupropion-naltrexone and reported a higher adjusted hazard of pancreatitis (hazard ratio 9.09, 95% confidence interval 1.25 to 66.00), alongside higher hazards of bowel obstruction and gastroparesis. · That confidence interval is as wide as it looks, and a claims-database design establishes association rather than causation. It is a signal, not a rate. No published retatrutide trial has been powered for pancreatitis, and a molecule activating the same receptors inherits the same unanswered question. A history of pancreatitis is a reason to raise this with a clinician before considering anything in this class.

    [5]

  • Pregnancy, planned pregnancy, and breastfeeding

    Not studied. The phase 2 obesity trial behind every weight figure on this page excluded participants who were pregnant, breastfeeding, or intending to become pregnant, and required adequate contraception in participants of childbearing potential. Nothing published reports retatrutide exposure during a human pregnancy. · Across incretin therapies, animal reproduction studies have reported embryofetal mortality, structural abnormalities, and reduced fetal growth at clinically relevant maternal exposures, and reviewers of the class recommend contraception to prevent unintended pregnancy during treatment. The approved GLP-1 labels direct discontinuation when a pregnancy is recognized, and the semaglutide labeling also directs stopping at least two months before a planned pregnancy because of that drug's long half-life. Retatrutide has no label to carry any such direction, no published reproductive-toxicology data of its own, and no prescriber in the loop. All of that is a class finding plus a regulatory absence, not a retatrutide finding. Pregnancy, intention to conceive, and breastfeeding are all reasons to raise this with a clinician before considering anything in this class.

    [7] [2]

  • Loss of lean body mass alongside fat mass

    Measured by DXA in a body-composition substudy of the phase 2 diabetes trial, in which the investigators concluded the proportion of lean mass lost relative to total weight lost was similar to other obesity treatments. · Reassuring as far as it goes, and it does not go far: of 189 substudy participants, only 103 completed treatment with both baseline and week-36 scans. Across incretin therapies generally, reported lean-mass loss varies widely and no trial has used strength or physical function as a primary endpoint.

    [11] [10]

  • Unverified identity and purity of material outside the trial supply chain

    Not quantified · With no approved manufacturer, nothing about the composition, concentration, or contaminant profile of material labeled "retatrutide" outside a sponsor trial is regulated or independently guaranteed. Every efficacy and safety number on this page was generated with pharmaceutical-grade product under trial monitoring, and none of it transfers automatically to anything else.

    [2]

Published lists are never exhaustive, so report anything unexpected to a licensed provider.

Storage, handling & reconstitution

Lyophilized storage
There is no lyophilized retatrutide anywhere in the studied supply chain. Every published result was generated with a sponsor-supplied ready-to-use injection solution, so no freeze-dried presentation of this compound has ever been manufactured to a standard, characterized for stability, or assigned an expiry by any manufacturer or regulator. This page therefore has no lyophilized-storage guidance to summarize, and general freeze-dried-peptide convention is not a retatrutide finding.
Reconstituted storage
The trials' injection solution was handled as investigational pharmaceutical material inside a sponsor's quality system: refrigerated, protected from light, and used within the sponsor's own assigned expiry. No published study establishes a solution shelf life for retatrutide outside that system, and no regulator or approved manufacturer has assigned a beyond-use date to anything sold under this name.
Reconstitution
Not applicable. Every published retatrutide result comes from a sponsor-supplied ready-to-use injection solution, and no lyophilized retatrutide exists in any studied supply chain. No reconstitution procedure for this compound appears anywhere in the published literature. There is nothing here to summarize, and this page will not improvise a procedure for material no published study has ever described preparing.
Handling notes
The gap between this compound's trial evidence and its regulatory status is the whole point of this section. Human trials used pharmaceutical-grade product manufactured and handled under a sponsor's quality system; nothing published extends any of those handling assumptions to material outside it.

The how-to guides cover the conventions behind these fields, and what the published stability data does and does not establish: Storage, Reconstitution, Handling.

Goal pages that include Retatrutide

Each one starts from the goal rather than the molecule, and grades what the evidence supports for that goal specifically.

  • Weight Loss

    A research reference for the incretin compounds mapped to weight loss, covering what the registrational trials measured, what happens when treatment stops, what the body-composition data show, and which parts of the picture come from a label rather than from a trial.

Questions for your provider

Bring this page to a licensed provider. A provider can order labs, review your medications and history, and tell you whether anything here is relevant to your situation. This page can't. Peptide Health Lab does not prescribe and does not sell peptides.

Want a structured starting point for that conversation? The Stack Builder turns your goals into a research-cited outline you can review together.

Citations

14 sources · every identifier checked against PubMed

Before you act on any of this

This page is educational only and is not medical advice. It does not diagnose, treat, or prescribe. Review it with a licensed provider before making any health decision. Peptide Health Lab does not sell peptides.

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