Tirzepatide vs Retatrutide: How the Two Compare

The short answer

Think of the two molecules as close cousins. Each one is a long, modified peptide chain built to copy natural gut hormones. Tirzepatide is called a "dual agonist" because it switches on two receptors. Retatrutide is called a "triple agonist" because it switches on three.

That one design choice is the main thing researchers are testing. The question in the trials is whether adding the glucagon receptor changes what the molecule does in the body, and what it costs in side effects.

Sources: Liu QK, Mechanisms of action and therapeutic applications of GLP-1 and dual GIP/GLP-1 receptor agonists, Front Endocrinol, 2024. Zafer M et al, Aliment Pharmacol Ther, 2025.

Side by side

This table pulls structure, targets and status into one place. Each cell comes from the source listed below it.

Our tirzepatide research vials and retatrutide research vials are sold for lab work only. Neither is a stand in for any medicine.

Sources: PubChem compound record CID 166567236 (tirzepatide), US National Library of Medicine. KEGG DRUG D12430, Retatrutide (USAN). Jastreboff AM et al, N Engl J Med, 2023. Therapeutic Goods Administration, Australian prescription medicine decision summary for tirzepatide, approved 22 December 2022, published 12 January 2023. Sport Integrity Australia, Retatrutide substance education page.

Tirzepatide action

GIP and GLP-1 are hormones the gut releases after a meal. They tell the pancreas to release insulin when blood sugar rises, and GLP-1 also slows how fast the stomach empties. Tirzepatide is one molecule that binds both of these receptors.

Reviews describe this as a step beyond older drugs that hit GLP-1 alone. A fatty side chain on the molecule helps it bind to albumin in the blood, so it lasts far longer than the natural hormones, which break down in minutes.

Sources: Liu QK, Mechanisms of action and therapeutic applications of GLP-1 and dual GIP/GLP-1 receptor agonists, Front Endocrinol, 2024.

Retatrutide action

Retatrutide keeps the GIP and GLP-1 activity and adds glucagon receptor activity. Glucagon is a hormone that usually raises blood sugar, so adding it may sound odd. Researchers study it because glucagon also affects how the liver handles fat and how much energy the body burns.

A 2025 review groups retatrutide with other "dual and triple agonists" being tested for fatty liver disease. It notes that much of the reasoning for the triple design comes from animal work and early human trials. For more on this molecule alone, see our guide on what retatrutide is.

Sources: Zafer M et al, Aliment Pharmacol Ther, 2025.

What trials examined

Both molecules have large trial programmes run by Eli Lilly. They were designed separately, years apart.

Tirzepatide trials

The SURPASS trials studied tirzepatide in type 2 diabetes. The SURMOUNT trials studied it in adults with obesity. SURMOUNT-1, published in 2022, enrolled 2,539 adults without diabetes and followed them for 72 weeks. Its main measures were the percent change in body weight and the share of people reaching set targets.

Retatrutide trials

A phase 2 trial published in 2023 enrolled 338 adults and ran for 48 weeks. Phase 3 has now reported in part. TRIUMPH-1, published in September 2026, enrolled 2,339 adults over 80 weeks and also looked at knee pain and sleep apnoea in subgroups. TRANSCEND-T2D-1, in the Lancet in 2026, looked at people with type 2 diabetes.

Why trials do not compare cleanly

It is tempting to line up numbers from SURMOUNT-1 and TRIUMPH-1. That can mislead. The trials enrolled different people, ran for different lengths of time and used different endpoints and analysis methods. A gap between two separate trials is not the same as a gap measured inside one trial.

Head to head trial

One trial does compare them directly. TRIUMPH-5 (NCT06662383) randomises adults with obesity to retatrutide or tirzepatide. Its record lists about 800 participants, and it was active but no longer recruiting as of July 2026. The record gives an estimated completion date of December 2026. No head to head findings had been published when this guide was written.

Sources: Jastreboff AM et al, N Engl J Med, 2022. Jastreboff AM et al, N Engl J Med, 2023. Jastreboff AM et al, N Engl J Med, 2026. Bajaj HS et al, Lancet, 2026. ClinicalTrials.gov, NCT06662383 (TRIUMPH-5): retatrutide compared with tirzepatide in adults with obesity, Record last updated July 2026.

Safety findings in trials

Across these trials, the most common adverse events for both molecules were gastrointestinal, meaning the stomach and bowel. Most were mild to moderate. In the 2023 retatrutide study, pulse rose, topped out around week 24, then fell back. The 2022 tirzepatide trial reported that a small share of people stopped because of side effects.

These are trial findings in supervised settings. They say nothing about the safety of products bought outside the medical system.

Sources: Jastreboff AM et al, N Engl J Med, 2022. Jastreboff AM et al, N Engl J Med, 2023. Jastreboff AM et al, N Engl J Med, 2026.

Status in Australia

Tirzepatide is a registered prescription medicine in Australia. The TGA approved it in December 2022, and healthdirect lists it as Schedule 4, prescription only. Whether any medicine suits a person is a question for their doctor, not for a research supplier.

Retatrutide has no TGA approval. Sport Integrity Australia warns that counterfeit retatrutide is being sold online illegally, sometimes labelled as a "research chemical", and says it is not on the 2026 Prohibited List, while GLP-1 drugs including tirzepatide sit on the WADA Monitoring Program. The TGA has also made clear that calling a product research only does not make selling it lawful.

Sources: Therapeutic Goods Administration, Australian prescription medicine decision summary for tirzepatide, approved 22 December 2022, published 12 January 2023. healthdirect Australia, Mounjaro (tirzepatide) medicine information, Schedule 4 Prescription Only Medicine. Sport Integrity Australia, Retatrutide substance education page. Therapeutic Goods Administration, Understanding your responsibilities when importing, compounding and supplying unapproved peptide products, Safety advisory, 13 April 2026.

Research use only

Glow Labs sells both compounds as lyophilised, or freeze dried, powder for lab research, as set out in our research use only notice. They are not medicines, are not for people and are not for animals. Each order leaves Gippsland tracked, and delivery takes 2-3 days. Certificates of analysis are available on request, and our peptide purity guide explains what they show.

FAQ

Sources: ClinicalTrials.gov, NCT06662383 (TRIUMPH-5): retatrutide compared with tirzepatide in adults with obesity, Record last updated July 2026. Therapeutic Goods Administration, Australian prescription medicine decision summary for tirzepatide, approved 22 December 2022, published 12 January 2023. Sport Integrity Australia, Retatrutide substance education page.