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Retatrutide

Also known as LY3437943, GLP-3 (community nickname), Reta, Triple G, Triple agonist (GIP, GLP-1, glucagon)

Investigational, not approvedMetabolic & weight loss

Last reviewed · Awaiting clinical review

Main safety concerns

Still investigational and not FDA approved. Do not use it if you or a close relative has had medullary thyroid cancer or MEN2. Nausea and other gut effects are common, and they flare after each dose increase.

Educational information, not medical advice. If you have symptoms that worry you, contact a clinician or emergency services.

What is known

An investigational once weekly injectable that switches on three metabolic hormone receptors at once and produced large weight loss in trials.

Status:
Still in trials and not approved anywhere. No approved retatrutide product exists yet.[6]
Strongest evidence for any claim:

See the evidence claim by claim

On this page

What it is and how it works

Retatrutide is a single molecule that activates three receptors tied to metabolism at the same time: , , and . The GLP-1 and GIP actions lower appetite and improve blood sugar control, while the glucagon action nudges up energy expenditure and fat burning. A fatty acid chain lets it stick to albumin in the blood, which is what stretches its life out to once weekly dosing. Some people call it GLP-3, but that is a community nickname, not a real receptor class.[1] [2]

Evidence by claim

Each claim is graded on its own. Tap a grade to see what it does and does not mean.

  • Produces large weight loss in adults with obesity, roughly 25 to 30 percent of body weight on the top dose depending on how the trial counts people who stopped early.

    Source type: Randomized trial, Manufacturer statement

    The pivotal phase 3 obesity trial (TRIUMPH-1) ran 2,339 people on 4, 9, or 12 mg against placebo. The May 2026 topline reported 17.6, 23.7, and 25.0 percent. The fuller results presented at the 2026 ADA Scientific Sessions ran higher for people who stayed on treatment, about 19, 26, and 28 percent at 80 weeks, reaching about 30 percent at 104 weeks on the top dose. The gap between the two is the difference between counting everyone and counting completers. Full peer reviewed publication is still pending.

    [2]New England Journal of Medicine 2023 (opens source in a new tab)· Randomized trial[5]Eli Lilly and Company 2026 (opens source in a new tab)· Manufacturer statement

  • Improves blood sugar in people with type 2 diabetes.

    Source type: Review

    Supported by phase 2 data pooled in a meta analysis. Not yet confirmed by completed phase 3 trials.

    [3]PMC (peer reviewed meta analysis) 2025 (opens source in a new tab)· Review

  • Reduces liver fat in fatty liver disease.

    Source type: Randomized trial

    From a phase 2a trial. Early but promising.

    [4]Nature Medicine 2024 (opens source in a new tab)· Randomized trial

  • Long term safety is still not established.

    Source type: Manufacturer statement, Regulatory record

    The phase 3 weight loss trials are done, but they were not built to answer this. The trial that is, TRIUMPH-Outcomes, is tracking heart and kidney events and is not estimated to finish until February 2029. So the honest state of things is that we now know retatrutide works and we still do not know what years of it do to you.

    [5]Eli Lilly and Company 2026 (opens source in a new tab)· Manufacturer statement[6]ClinicalTrials.gov 2026 (opens source in a new tab)· Regulatory record

Reported side effects

  • SeriousAcute pancreatitis(rare)[2]One serious case in the phase 2 obesity trial, along with symptomless rises in pancreatic enzymes. Seek care for severe, lasting abdominal pain.
  • CautionNausea(common)[2]The most common effect. It tends to spike in the days after each dose increase, then settle.
  • CautionVomiting or diarrhea(common)[2]
  • CautionConstipation(common)[2]
  • CautionFaster heart rate(common)[2]A known effect across this drug class.
  • CautionTingling or altered skin sensation(uncommon)[2]Reported as mild to moderate in trials, and it did not cause people to stop.
  • InfoReduced appetite(common)[2]Expected, and part of how the drug works.

Interactions and combination risks

  • WarningInsulin or sulfonylureas[2]

    Raises the risk of low blood sugar. These medicines may need to be lowered under medical supervision.

  • CautionOral medications[2]

    Retatrutide slows stomach emptying, which can change how quickly swallowed drugs are absorbed.

  • WarningOther GLP-1 or incretin drugs (semaglutide, tirzepatide)

    Stacking with another incretin agonist is not studied and raises the chance of severe gut effects.

Who should avoid it

  • SeriousPersonal or family history of medullary thyroid cancer, or MEN2

    Drugs in this class caused thyroid C cell tumors in rodents. No human cases have shown up in trials, but the precaution stands.

  • SeriousPregnancy or breastfeeding

    No safety data, and rapid weight loss is not advised during pregnancy.

  • WarningHistory of pancreatitis

    A possible pancreatitis signal means extra caution is warranted.

Dosing

Placed after the evidence and risks on purpose. Nothing here is a recommendation for you.

Doses studied in human trials
Route(s)subcutaneous, once weekly
Typical rangeTrials have used 1 mg up to 12 mg once weekly. The phase 3 obesity trial started everyone at 2 mg and settled at 4, 9, or 12 mg. The example low schedule below, which no trial tested, starts lower than all of it.
FrequencyOnce weekly
Half life used in the model6 days
Cycle guidanceDoses get raised in steps, never jumped to. Phase 3 stepped up every 4 weeks along 2, 4, 6, 9, and 12 mg so the gut had time to adjust at each level.
NotesWith a around 6 days, retatrutide builds up over the first month of steady dosing before it levels off at a plateau. This is why gut side effects often ease a few weeks into a given dose, and why raising the dose too quickly tends to bring them back. Try the plotter below to see the buildup.
[1] [2] [5]

Not tested in any trial

Example low schedule, assembled by the editors

Built from the trial doses above, but no study ran this sequence. It is shown to explain the reasoning about staying low, not as a protocol to follow.

The trial data give little reason to keep climbing once a dose is working. In the phase 3 obesity trial, 4 mg per week took off about 17.6 percent of body weight, and 4.1 percent of people quit over side effects, which is about the same share as the people on placebo. Climbing to 12 mg bought roughly 7 more points of weight loss and nearly tripled that quit rate to 11.3 percent. Most of the benefit shows up early on the ladder and most of the misery shows up at the top of it. There is no prize for climbing.

  1. 1

    1 mg once weekly

    Held for 4 to 6 weeks

    Half the dose phase 3 started people on. A gentler introduction for your gut, and the entire point of starting here.

  2. 2

    2 mg once weekly

    Held for 4 to 6 weeks

    In this example, a step up only follows a full window at 1 mg without enough effect. A bad week is not a full window.

  3. 3

    4 mg once weekly

    Held for 4 to 6 weeks

    The lowest dose phase 3 studied, and it delivered about 70 percent of the weight loss that 12 mg did while barely moving the quit rate. Plenty of people have no good reason to go past this step.

  4. 4

    6 mg once weekly

    Held for as long as it keeps working

    Where this example stops. Also a real step on the phase 3 ladder rather than a number we made up.

Ceiling: 6 mg once weekly

Trials went to 12 mg, so higher doses are studied and they do move the scale further. This example stops at 6 mg anyway. Side effects climb at every step, and the trial that will tell us what retatrutide does to hearts and kidneys over years does not report until 2029, so nobody knows the long term picture yet at any dose. Going past 6 mg is not something this page can support. If 6 mg is not doing what was hoped, that is a conversation for a clinician.[5] [6]

No trial ran this ladder. Phase 3 started at 2 mg and stepped up every 4 weeks to 4, 9, or 12 mg. This example starts lower, moves slower, and stops earlier than that. It is a cautious reading of strong trial data, not a tested regimen. That is why it is graded below the dosing data it is built on.

Educational information, not medical advice or a prescription.[2] [5]

For the equipment itself, see syringes, needles, and the rest of the kit.

Saturation model (simplified)

A textbook one compartment model of how Retatrutide could build up with repeated doses. It is a shape, not a measured blood level. The starting values mirror the table above for illustration only.

This is not syringe units. The dose below is the actual amount of compound, in micrograms (mcg) or milligrams (mg). If you only know your dose as units on the syringe, use the reconstitution calculator to convert units to mcg or mg first.
Simplified model

Modeled amount in the body over time

Assumes evenly spaced doses, instant absorption, and one compartment first order clearance at the half life you entered. The vertical axis is modeled amount remaining in mg, not a measured blood concentration, and real levels vary between people.

02468wk 02468101214plateau average

Plateau average (modeled)

4.9 mg

Peak / trough

7.2 / 3.2

Time to about 90% of plateau

2.8 wk

Share of plateau at cycle end

100%

Retatrutide: in this model the amount reaches about 90% of its plateau after 2.8 weeks, and is at 100% of that plateau when dosing stops at week 12.

Show the modeled values as a table
Modeled amount by week, in mg
WeekRetatrutide (mg)
04
15.8
26.6
36.9
47.1
57.2
67.2
77.2
87.2
97.2
107.2
117.2
123.2
131.4
140.6

An educational estimate, not a clinical simulation or dosing advice.

Reconstitution

Vial sizes5 mg, 10 mg, 15 mg
DiluentBacteriostatic water for multi dose vials, or sterile water for single use
ConcentrationExample: a 10 mg vial plus 1 mL of water gives 10 mg/mL, so 4 mg is 0.4 mL, which is 40 units on a U-100 syringe. Adjust the water volume to land on an easy unit count.
NotesA finished retatrutide product is expected to arrive as a prefilled pen. Research material is sold as lyophilized (freeze dried) vials, commonly 5 mg to 15 mg.

General reconstitution technique

Units and volume arithmetic

Converts between an amount and syringe units for the vial and diluent you enter. It starts empty and does not suggest an amount. Open the full calculator

Inputs

What do you want to convert?
  1. mg

    Total amount printed on the vial label.

    Sizes sold:
  2. mL

    Volume of bacteriostatic water already in the vial.

  3. Check the unit. 1 mg = 1,000 mcg, so the wrong one is a 1,000x error.

  4. U-100

    Printed on the syringe wrapper. Results over this size are shown as invalid.

Result

Fill in steps 1 to 3 to see the arithmetic. Nothing here is a suggested amount.

Settings live in the address bar, so a pasted link reopens this calculator as you left it.

Educational arithmetic only. It does not choose an amount for you and is not medical or dosing advice. Verify every calculation independently.

Storage and stability

Dry powder (lyophilized)

TemperatureFreeze for long term storage, or 2 to 8 short term
Shelf lifeMany months when frozen
NotesKeep dry and out of light until you mix it.

After mixing

Temperature2 to 8 (refrigerated)
Shelf lifeAbout 4 weeks
NotesDo not freeze after mixing. Discard if the solution turns cloudy.

General storage and stability guide

COA and purity notes

Common adulterantsunderdosed or mislabeled vials, retatrutide sold as a blend with other GLP-1 drugs, endotoxin or contaminants from non sterile production
MislabelingBecause there is no approved retatrutide product yet, all research material is unregulated. Actual content can differ from the label, so a recent third party COA matters.
NotesNot FDA approved. The quality of research material is not overseen by any regulator.

How to read a COA

Sources

  1. [1]LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b multiple ascending dose trial

    The Lancet 2022 (opens source in a new tab)· Randomized trial

  2. [2]Triple Hormone Receptor Agonist Retatrutide for Obesity, a Phase 2 Trial

    New England Journal of Medicine 2023 (opens source in a new tab)· Randomized trial

  3. [3]Efficacy and safety of retatrutide for obesity: a systematic review and meta analysis of randomized controlled trials

    PMC (peer reviewed meta analysis) 2025 (opens source in a new tab)· Review

  4. [4]Triple hormone receptor agonist retatrutide for metabolic dysfunction associated steatotic liver disease: a randomized phase 2a trial

    Nature Medicine 2024 (opens source in a new tab)· Randomized trial

  5. [5]Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1 topline results, announced 21 May 2026)

    Eli Lilly and Company 2026 (opens source in a new tab)· Manufacturer statement

  6. [6]The Effect of Retatrutide Once Weekly on Cardiovascular Outcomes and Kidney Outcomes in Adults Living With Obesity (TRIUMPH-Outcomes), NCT06383390. Estimated completion February 2029.

    ClinicalTrials.gov 2026 (opens source in a new tab)· Regulatory record

Last reviewed 16 July 2026 · editorial status: reviewed