Skip to content
Easy Peptide Info
Menu
Investigational drug

What is retatrutide?

Retatrutide explained in plain English: what it is, what the research shows, side effects, legal status and dosage, plus a calculator for syringe units. Doses shown come only from the label or published trials, each with its source. Also called Reta, Reta peptide, LY3437943, "GLP-3", "GLP3" or "GLP 3" (nickname).

Retatrutide is an investigational drug: it is not approved by the FDA or any other regulator yet. This page is educational; talk with a qualified healthcare professional.

Calculate
Vial unit

= 10,000 mcg

mL
Dose unit
Syringe type
Syringe size

Units to draw

–units

Enter your dose.

Syringe, no result yetU-100, 1 mL syringe holding up to 100 units. Enter your dose.0102030405060708090100

Saved calculations

No saved calculations yet. Save one from the results.

What is retatrutide?

Retatrutide is an investigational weight-loss drug made by Eli Lilly. It is a peptide that copies three natural gut hormones at once, which is why people online call it “reta” or “GLP-3.”

It is given as a weekly injection in clinical trials. It is not approved by the FDA or any other regulator yet, so it is only legally available to people taking part in those trials.

Whether you see it called “retatrutide peptide,” “reta peptide,” “peptide reta” or just “reta,” it is the same drug.

What does retatrutide do?

Retatrutide turns on three hormone receptors: GLP-1, GIP and glucagon. Together they lower appetite, slow how fast the stomach empties and may raise the energy the body uses.

Drugs like semaglutide act on one of these receptors and tirzepatide on two. Adding the glucagon receptor is the new part, and researchers think it helps explain the size of the weight loss seen so far.

What do the retatrutide trials show?

Retatrutide has produced some of the largest weight loss seen with any drug in trials. In the phase 2 trial published in 2023, people on the highest dose lost an average of about 24% of their body weight in 48 weeks.

The larger phase 3 TRIUMPH trials reported similar results in 2026:

  • TRIUMPH-1 (obesity or overweight, about 2,300 people): an average of 28.3% weight loss at 80 weeks on the highest dose, and 30.3% in a group followed to 104 weeks.
  • TRIUMPH-2 (obesity with type 2 diabetes): up to 20.8% average weight loss at 80 weeks, with better blood sugar.
  • TRIUMPH-3 (severe obesity with heart disease): up to 22.6% average weight loss at 80 weeks.
  • TRIUMPH-4 (obesity with knee arthritis): 28.7% average weight loss at 68 weeks, with less knee pain.

These are averages from trials with medical supervision and slow dose increases. Results in any one person can be very different.

Retatrutide (reta peptide) side effects

The most common side effects are stomach-related: nausea, diarrhea, constipation and vomiting. They were most common at higher doses and while the dose was being increased, and were mostly mild to moderate.

In TRIUMPH-1, about 4 to 11% of people on retatrutide stopped because of side effects, depending on the dose, compared with about 5% on placebo. Some people also reported dysesthesia, a tingling, burning or unusual skin feeling, which mostly settled during treatment.

Because retatrutide is still being studied, its long-term risks aren’t fully known. Drugs in the same family carry warnings about pancreatitis, gallbladder problems and low blood sugar when combined with some diabetes medicines.

Retatrutide is not approved anywhere, so there is no legal prescription price. Eli Lilly has said it plans to apply for FDA approval in the first quarter of 2027.

Products sold online as “retatrutide” or “reta” are unapproved research chemicals. Nobody checks what is in them, how pure they are or whether the amount on the label is right.

How do you reconstitute retatrutide?

In trials, retatrutide is given by trained staff. If you are working with a powder vial, the calculator above turns the vial size, the bacteriostatic water and a dose into syringe units, and the reconstitution guide explains each step.

See the dosage section below for what is known about doses, with sources.

Retatrutide dosage in clinical trials

Retatrutide is not approved, so there is no approved dose. In the phase 3 TRIUMPH trials, people started at 2 mg once a week and stepped up every 4 weeks to a target of 4, 9 or 12 mg.

Doses tested in published clinical trials. They are not approved doses, and trial participants were closely monitored.

Retatrutide doses, with sources
WhenDoseHow often
TRIUMPH phase 3, start2 mg[1]Once a week
TRIUMPH phase 3, steps every 4 weeks2 → 4 → 6 → 9 → 12 mg[1]Once a week
TRIUMPH phase 3, target doses4 mg, 9 mg or 12 mg[1]Once a week
Phase 2 trial, doses tested1 mg to 12 mg[2]Once a week
  1. Eli Lilly (2026), TRIUMPH-1 phase 3 results
  2. Jastreboff et al. (2023), Retatrutide phase 2 trial, NEJM

Medical disclaimer: this dosage information is for education only and comes from the source shown for each row. It is not medical advice and not a recommendation for you. Only a licensed prescriber who knows your health can decide whether Retatrutide is right for you and at what dose. Don't start, change or stop a medicine based on this page, and don't use research peptides or unapproved drugs based on trial doses.

Retatrutide concentration chart

The concentration of a Retatrutide vial depends only on its size and the water you add. Each unit on a U-100 syringe holds one hundredth of a mL.

Retatrutide concentration by vial size and water
Vial + waterConcentrationPer unit (U-100)
5 mg + 1 mL5,000 mcg/mL (5 mg/mL)50 mcg per unit (0.05 mg per unit)
5 mg + 2 mL2,500 mcg/mL (2.5 mg/mL)25 mcg per unit (0.025 mg per unit)
5 mg + 3 mL1,666.67 mcg/mL (1.66667 mg/mL)16.67 mcg per unit (0.01667 mg per unit)
10 mg + 1 mL10,000 mcg/mL (10 mg/mL)100 mcg per unit (0.1 mg per unit)
10 mg + 2 mL5,000 mcg/mL (5 mg/mL)50 mcg per unit (0.05 mg per unit)
10 mg + 3 mL3,333.33 mcg/mL (3.33333 mg/mL)33.33 mcg per unit (0.03333 mg per unit)
20 mg + 1 mL20,000 mcg/mL (20 mg/mL)200 mcg per unit (0.2 mg per unit)
20 mg + 2 mL10,000 mcg/mL (10 mg/mL)100 mcg per unit (0.1 mg per unit)
20 mg + 3 mL6,666.67 mcg/mL (6.66667 mg/mL)66.67 mcg per unit (0.06667 mg per unit)

Frequently asked questions

What does retatrutide do?

It acts like three gut hormones at once (GLP-1, GIP and glucagon), which lowers appetite, slows digestion and may increase the energy the body burns. In trials this led to large weight loss.

What are the reta peptide side effects?

The most common are nausea, diarrhea, constipation and vomiting, mostly while the dose is being raised. Some people in trials also reported a tingling or burning skin feeling called dysesthesia.

What is GLP3 (GLP-3)?

"GLP3" (also written GLP-3 or GLP 3) is an internet nickname for retatrutide, because it acts on three hormone receptors. It is not a real hormone or an official drug name.

How much does GLP3 (retatrutide) cost?

There is no official GLP3 cost or retatrutide price, because retatrutide is not approved or sold as a medicine yet. Products sold online as retatrutide are unapproved research chemicals, and their contents are not checked.

Is retatrutide FDA approved?

No. As of October 2026 retatrutide is still investigational. Eli Lilly has said it plans to ask the FDA for approval in early 2027.

Is retatrutide stronger than tirzepatide or semaglutide?

In separate trials, retatrutide produced more average weight loss than has been reported for those drugs, but no head-to-head trial has been published, so a direct comparison isn't possible yet.

Sources

  1. Jastreboff et al. (2023), Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial, New England Journal of Medicine
  2. AJMC (2026), Retatrutide Achieves Up to 30.3% Average Weight Loss in Phase 3 TRIUMPH-1 Trial
  3. Eli Lilly, retatrutide successful in two additional Phase 3 obesity trials

Last updated .

More peptide guides and calculators