What Is Retatrutide? How It Works and Its Trial Status

Retatrutide in brief

Retatrutide is a single lab-made peptide chain. It is designed to switch on three different receptors. Most earlier compounds in this family act on one receptor, or on two. That three-way action is why researchers call it a triple agonist. It is also why online posts often give it the nickname "GLP-3".

That nickname is informal. There is no hormone called GLP-3. The trial papers do not use the name. In everyday talk it is also called "reta".

Sources: Coskun T et al, Cell Metab, 2022. Sport Integrity Australia, Retatrutide (Reta) explained, Substance education.

The three receptors

A receptor is a protein on the surface of a cell. When the right molecule fits it, the cell responds. Retatrutide is designed to fit three of them. Here is what each receptor does as part of normal biology.

• GLP-1 receptor: responds to glucagon-like peptide 1, a gut hormone released after eating. It is involved in insulin release and in signals about fullness.
• GIP receptor: responds to glucose-dependent insulinotropic polypeptide, another gut hormone. It helps control insulin release after a meal.
• Glucagon receptor: responds to glucagon, a hormone from the pancreas. It tells the liver to release stored sugar. It is also studied for its role in how the body uses energy.

Sport Integrity Australia notes that these hormones are linked with glucose control and insulin release. They are also linked with hunger. The Lilly team tested the molecule in cells for its discovery paper. Its activity at the glucagon and GLP-1 receptors was balanced. It was more active at the GIP receptor.

Sources: Coskun T et al, Cell Metab, 2022. Sport Integrity Australia, Retatrutide (Reta) explained, Substance education.

What it is made of

Retatrutide is a chain of 39 amino acids. That length is listed in the US Food and Drug Administration's substance registry. KEGG DRUG lists it as a modified peptide. Its formula and weight below are for that full modified molecule.

There is no PubChem compound record for retatrutide by name. These figures come from the FDA registry and KEGG DRUG instead.

Sources: FDA Global Substance Registration System, Retatrutide (UNII NOP2Y096GV): 39-residue sequence. KEGG DRUG D12430, Retatrutide (USAN): formula and molecular weight.

The trials so far

Retatrutide has moved through each stage of clinical testing. Below are the main published trials. Each one shows its size, its length and what it measured.

Phase 2 trials

• Obesity, 2023: a trial of 338 adults ran for 48 weeks. Its main measure was the percent change in body weight.
• Type 2 diabetes, 2023: a US trial took 281 adults. It looked mainly at HbA1c, a long-term blood sugar measure, over 24 weeks. Body weight was a later measure at 36 weeks.
• Liver fat, 2024: a phase 2a substudy took 98 people from the obesity trial. It measured liver fat in people with a condition called metabolic dysfunction-associated steatotic liver disease.

Phase 3 trials

The phase 3 programme is called TRIUMPH. Its design paper describes four trials in more than 5,800 people. They test the compound in obesity and in two related conditions. Those are knee osteoarthritis and obstructive sleep apnoea.

• TRIUMPH-1, 2026: 2,339 adults with obesity but without diabetes took part for 80 weeks. Its main measure was the percent change in body weight. The trial also measured knee pain and breathing pauses during sleep in subgroups.
• Type 2 diabetes, 2026: a 40-week phase 3 trial took 537 adults in the USA, Mexico and India. It studied retatrutide as the only diabetes treatment. It measured HbA1c and body weight.

These trials ran under strict conditions, with medical supervision. What they found does not predict what would happen to anyone.

Sources: Jastreboff AM et al, Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial, N Engl J Med, 2023. Rosenstock J et al, Lancet, 2023. Sanyal AJ et al, Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial, Nat Med, 2024. Giblin K et al, Diabetes Obes Metab, 2026. Jastreboff AM et al, Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1), N Engl J Med, 2026. Bajaj HS et al, Lancet, 2026.

Adverse events

Every trial paper reports side effects. Across the trials, the most common were gastrointestinal: nausea, diarrhoea, vomiting and constipation.

• In the 2023 obesity trial, these events were more frequent in higher study arms. Most were mild to moderate. Heart rate rose, peaked at 24 weeks and then declined.
• In the 2023 diabetes trial, 35 percent of people on retatrutide reported mild to moderate gastrointestinal events. On placebo, the figure was 13 percent.
• In the 2026 phase 3 diabetes trial, 2 to 5 percent of people on retatrutide stopped because of adverse events. No one on placebo stopped for that reason.

Sport Integrity Australia adds that the long-term safety of retatrutide has not been fully studied. It says this remains relatively unknown. A 2025 review that pooled three trials called for larger and longer studies.

Sources: Jastreboff AM et al, Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial, N Engl J Med, 2023. Rosenstock J et al, Lancet, 2023. Bajaj HS et al, Lancet, 2026. Abdrabou Abouelmagd A et al, Proc (Bayl Univ Med Cent), 2025. Sport Integrity Australia, Retatrutide (Reta) explained, Substance education.

Vs tirzepatide

Tirzepatide is the closest relative. Both are 39 amino acid peptides. Tirzepatide targets the GIP and GLP-1 receptors. Retatrutide targets those two and the glucagon receptor too. The other key difference is status. In Australia, tirzepatide is a registered prescription medicine sold as Mounjaro. Retatrutide is not approved anywhere.

For a full side by side, read our guide to tirzepatide vs retatrutide.

Sources: FDA Global Substance Registration System, Retatrutide (UNII NOP2Y096GV): 39-residue sequence. Therapeutic Goods Administration, Australian Product Information summary: Mounjaro (tirzepatide), AusPMD.

Status in Australia

Here is where retatrutide stands in Australia.

Sport Integrity Australia also says counterfeit peptides, including retatrutide, are being sold online illegally. Some are labelled as "research chemicals" or "not for human consumption". It says their purity and concentration are often unknown. They may also be contaminated with substances banned in sport. In June 2026 the Victorian Department of Health issued a health alert. It was about liver toxicity linked to products labelled Retatrutide. Our peptide purity guide explains how labs test what is in a vial.

Sources: Sport Integrity Australia, Retatrutide (Reta) explained, Substance education. Therapeutic Goods Administration, Unapproved peptide product promoters and suppliers are put on notice, Media release, 20 July 2026. Therapeutic Goods Administration, Understanding your responsibilities when importing, compounding and supplying unapproved peptide products, Safety advisory, 13 April 2026. Department of Health, Victoria, Toxicity linked to unapproved peptide product labelled Retatrutide, Health alert, 19 June 2026. Australian New Zealand Clinical Trials Registry, Trial search: retatrutide (seven records, searched October 2026).

Research use only

Glow Labs supplies retatrutide as a freeze-dried research compound for laboratory study only. It is not the trial medicine, and it is not approved for human consumption. Nothing on this page is medical advice. Orders are sent from Gippsland, Victoria, with tracked delivery across Australia in 2-3 days. For handling the powder, see how to store peptides.

FAQ

Sources: Jastreboff AM et al, Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial, N Engl J Med, 2023. Sport Integrity Australia, Retatrutide (Reta) explained, Substance education. Therapeutic Goods Administration, Australian Product Information summary: Mounjaro (tirzepatide), AusPMD.