What it is

Retatrutide is an investigational triple agonist: it acts on the GLP-1, GIP and glucagon receptors at once. That third arm is what separates it from the dual agonists that came before it, and it is the reason its synthesis is more demanding than a GLP-1 compound like semaglutide.

It is worth clearing up a naming problem you will see on vendor listings. Retatrutide is sometimes sold as “GLP-3”. There is no such receptor. The label is a marketing invention, and its presence on a product page is a reasonable early signal about how carefully that vendor describes what it sells.

Retatrutide is not an approved medicine in any jurisdiction. It is in clinical trials, and material sold on the research market is not clinical-grade product.

What does the research on retatrutide actually show?

Retatrutide has completed Phase 3. On 21 May 2026 Eli Lilly reported results from TRIUMPH-1, in which 2,339 adults with obesity were randomised for 80 weeks: the 12 mg dose produced 28.3% mean weight loss against 2.2% on placebo. That makes retatrutide the most clinically advanced compound covered anywhere on this site, and it is still not an approved medicine in any country.

Weekly dose	Mean weight loss	In pounds	Stopped for adverse events
4 mg	19.0%	47.2 lb	4.1%
9 mg	25.9%	64.4 lb	6.9%
12 mg	28.3%	70.3 lb	11.3%
Placebo	2.2%	5.5 lb	4.9%

The earlier Phase 2 trial, published in the New England Journal of Medicine in 2023, enrolled 338 adults and ran 48 weeks. Mean weight change at 48 weeks was -24.2% on 12 mg retatrutide against -2.1% on placebo, and 75% of the 8 mg group lost at least 15% of body weight. Both trials used pharmaceutical-grade retatrutide manufactured under GMP by the sponsor.

How well is retatrutide tolerated in trials?

The adverse events reported in TRIUMPH-1 were mostly gastrointestinal: nausea, diarrhoea and constipation, and mostly mild to moderate. Dysesthesia, a skin sensitivity described as tingling or burning, occurred in 5.1%, 12.3% and 12.5% of the 4 mg, 9 mg and 12 mg groups respectively. Discontinuation because of adverse events rose with dose, from 4.1% at 4 mg to 11.3% at 12 mg, against 4.9% on placebo.

What this evidence does not cover

Primary sources

• Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. N Engl J Med, 2023 (PMID 37366315)
• Eli Lilly. TRIUMPH-1 Phase 3 topline results, 21 May 2026
• ClinicalTrials.gov NCT05929066: TRIUMPH-1 (completed)
• ClinicalTrials.gov NCT04881760: Phase 2 (completed)
• Retatrutide on Wikipedia

The pricing problem

Retatrutide has one of the widest price spreads we track. Quotes run from roughly $300 per single milligram for analytical reference standards down to about $375 for a 30 milligram vial. That is a difference of more than an order of magnitude per milligram.

Both numbers can be legitimate. A certified reference standard is a different product from bulk research material, sold for a different purpose. The problem is that vendor listings rarely tell you which one you are looking at.

Price per effective milligram

A headline price per milligram is misleading when purity varies, because you are paying for the impurity fraction too. The figure that matters is cost per effective milligram, meaning price divided by the mass that is actually the target sequence.

Two listings from our price analysis show how this inverts a decision. A 10 mg vial at $110 with 99.4 percent purity works out to $1.11 per effective milligram. A cheaper vial at $95 with 91 percent purity works out to $1.04 per effective milligram. Nominally the better deal, while carrying a 9 percent impurity load into the experiment.

Whether that saving is worth an unknown 9 percent contaminant is a judgement call. But it should be made knowingly, and a per-milligram price alone hides it. Independently re-testing a suspicious batch typically costs $300 to $500 per sample, which is the number to weigh against the saving.

What to check on the documentation

For retatrutide specifically, identity matters as much as purity. The triple-agonist sequence is long and expensive to synthesise correctly, which creates an incentive to substitute a cheaper dual agonist and label it as retatrutide.

That makes mass spectrometry the critical document rather than HPLC alone: HPLC tells you how pure the sample is, mass spectrometry tells you whether it is the right molecule. A certificate showing purity but no identity confirmation does not answer the question that matters here. Check also that the batch or lot number on the certificate matches the batch being sold.

Our Retatrutide analysis

Reconstitution calculator

Work out the concentration and the units on the syringe from what is printed on your vial. Arithmetic only — it does not recommend a dose. More on how it works.