Retatrutide in Australia: an investigational medicine, not an approved one.
Retatrutide (LY3437943) is an experimental medicine from Eli Lilly that has produced some of the largest average weight losses reported in obesity trials. That is why it is heavily searched, and why unapproved products carrying its name are being sold online. This page sets out what retatrutide is, every trial result reported to date, its regulatory position as of 20 October 2026, and the safety alerts and enforcement action Australian authorities have issued.
Retatrutide is an investigational once-weekly injection from Eli Lilly that activates three hormone receptors (GIP, GLP-1 and glucagon). As of 20 October 2026 it is not approved by the TGA or any comparable regulator, and it is legally available only inside Lilly's clinical trials. Products sold online as retatrutide or "Reta" are unapproved, and Australian health authorities have linked them to liver injury and a torn oesophagus.
- Not approved anywhere. The TGA states that retatrutide "has not been approved by the TGA or any comparable international regulator". Source: TGA safety alert, 14 September 2026.
- Not on the ARTG, and unlawful to supply. Retatrutide products are unapproved therapeutic goods. The TGA: "It is unlawful to import, advertise, manufacture and supply unapproved peptide products in Australia." Source: TGA media release, 17 August 2026.
- Trials only. Lilly says retatrutide is "legally available only to participants in Lilly's clinical trials" and "cannot be legally sold or marketed for human use". Source: Lilly, 23 July 2026.
- No filing anywhere yet. Lilly plans to submit a Biologics License Application to the US FDA in the first quarter of 2027. No Australian approval date exists. Source: Lilly, 29 September 2026.
- Active safety alerts. Victoria's Chief Health Officer has linked unapproved products labelled Retatrutide to six cases of acute liver injury (19 June 2026), and the TGA has reported a counterfeit "retatrutide" vial that contained undeclared semaglutide (14 September 2026). Sources: Victorian Department of Health; TGA.
What is retatrutide?
Retatrutide is a single, laboratory-made peptide that activates three hormone receptors at once: GIP, GLP-1 and glucagon. In trials it is given as an injection once a week, and it has a half-life of about six days.
The medicines already registered in Australia for weight management act on fewer of these receptors. Semaglutide (Ozempic, Wegovy) is a GLP-1 receptor agonist. Tirzepatide (Mounjaro) activates two receptors, GIP and GLP-1. Retatrutide adds the glucagon receptor, which is why the 2023 Phase 2 paper in the New England Journal of Medicine calls it a "triple-hormone-receptor agonist". The retatrutide vs tirzepatide comparison covers the difference in detail.
The same paper reports how strongly retatrutide acts at each receptor compared with the body's own hormones. It is less potent at the human glucagon receptor (about 0.3 times) and the GLP-1 receptor (about 0.4 times), and more potent at the GIP receptor (about 8.9 times).
Retatrutide is not a supplement or a "research chemical". Lilly describes it as investigational, and it has been studied in obesity, type 2 diabetes, knee osteoarthritis pain and obstructive sleep apnoea. In July 2026 Lilly said it had the data package "to support global submissions" for obesity, knee osteoarthritis pain and sleep apnoea. Having data to submit is not the same as approval: no regulator has yet assessed the full data set.
What did the retatrutide trials show?
In every trial reported so far, people taking retatrutide lost substantially more weight on average than people taking placebo, with the largest losses usually on the 12 mg dose. Of the results below, the Phase 2 trial, TRANSCEND-T2D-1 and TRIUMPH-2 have journal publications; the rest are company-reported toplines.
| Trial | Who took part | Doses and length | Main result (highest dose) | Reported |
|---|---|---|---|---|
| Phase 2 | 338 adults with obesity, or overweight plus a weight-related condition; no diabetes | 1, 4, 8, 12 mg vs placebo; 48 weeks | Weight −24.2% (12 mg) vs −2.1% placebo | NEJM, 26 June 2023 |
| TRIUMPH-4 | 445 adults with obesity or overweight and knee osteoarthritis; no diabetes | 9, 12 mg vs placebo; 68 weeks | Weight −28.7% vs −2.1% (efficacy); −23.7% vs −4.6% (treatment-regimen) | Lilly topline, 11 December 2025 |
| TRANSCEND-T2D-1 | 537 adults with type 2 diabetes managed by diet and exercise | 4, 9, 12 mg vs placebo; 40 weeks | A1C −1.9% vs −0.8% (baseline 7.9%); weight −16.8%, still falling at 40 weeks | Topline 19 March 2026; The Lancet, June 2026 |
| TRIUMPH-1 | 2,339 adults with obesity or overweight plus a related condition; no diabetes | 4, 9, 12 mg vs placebo; 80 weeks | Weight −28.3% vs −2.2% (efficacy); −25.0% vs −3.9% (treatment-regimen) | Lilly topline, 21 May 2026 |
| TRIUMPH-2 | 1,152 adults with obesity or overweight and type 2 diabetes | 4, 9, 12 mg vs placebo; 80 weeks | Weight −20.8% vs −4.0%; A1C −1.5% vs −0.2% (baseline 7.7%) | Topline 23 July 2026; The Lancet, 29 September 2026 |
| TRIUMPH-3 | 1,949 adults with a BMI of 35 or more and established cardiovascular disease | 9, 12 mg vs placebo; 80 weeks | Weight −22.6% vs −3.2%; heart-event results not statistically significant | Lilly topline, 23 July 2026 |
Phase 3 figures use the efficacy estimand unless marked. TRIUMPH-1 to TRIUMPH-4 and TRANSCEND-T2D-1 are the five Phase 3 studies Lilly described as positive in July 2026. Sources: NEJM Phase 2 paper and Lilly releases listed below.
Beyond the averages. In the Phase 2 trial, everyone on 12 mg lost at least 5% of body weight by 48 weeks, 93% lost at least 10% and 83% lost at least 15%, compared with 27%, 9% and 2% on placebo; 26% on 12 mg lost 30% or more. In TRIUMPH-1, 45.3% of the 12 mg group lost 30% or more.
Other outcomes. In TRIUMPH-4, the WOMAC knee-pain score fell by 4.4 points (74.3%) on 12 mg, compared with 2.4 points (40.3%) on placebo. In the TRIUMPH-1 sub-trials, knee pain fell by up to 4.3 points and the apnoea–hypopnoea index in people with moderate-to-severe sleep apnoea fell by up to 36.1 events an hour (60.6%). In TRANSCEND-T2D-1, up to 46% of participants reached an A1C below 5.7%.
How should retatrutide results be read?
With care: the headline figures are averages from closely supervised trials, usually calculated the more favourable of two ways, in populations that differ from trial to trial.
- Two estimands. The "efficacy estimand" estimates the result if everyone had stayed on treatment. The "treatment-regimen estimand" counts everyone, whether or not they stopped. Lilly's headline numbers use the first, which is larger: 28.3% versus 25.0% on 12 mg in TRIUMPH-1.
- The 30% figure is a subgroup. A widely shared figure of 30.3% comes from a 104-week extension of TRIUMPH-1 in 532 people with a BMI of 35 or more who tolerated their dose. It is not the main 80-week result.
- Diabetes changes the picture. People with type 2 diabetes lost less on average: 20.8% in TRIUMPH-2, against 28.3% in TRIUMPH-1. These are different trials, so the gap is indicative only.
- Heart outcomes are unresolved. In TRIUMPH-3, the hazard ratios for major cardiovascular events (MACE-5 0.82, 95% CI 0.55–1.22; MACE-3 1.12, 0.64–1.96) were not statistically significant, and there were fewer events than expected. The trial neither shows a heart benefit nor rules out a risk.
- Still to come. Lilly says the TRIUMPH-2 sleep apnoea sub-trial "will be presented at a future medical meeting". The head-to-head trial against tirzepatide, TRIUMPH-5, has not reported.
Side effects were common and led some participants to stop. The retatrutide side effects guide sets out the rates trial by trial.
Has retatrutide caused harm in Australia?
The Australian alerts concern unapproved products sold under the retatrutide name, not the medicine studied in Lilly's trials. Victoria has reported acute liver injury in people who used them, and the TGA has reported a counterfeit vial that led to hospital treatment.
| Date | Issued by | What it says |
|---|---|---|
| 7 May 2026 | TGA | Warning on importing unapproved peptides. Products identified only by codes, or without a clear active ingredient and strength, will not be released under the Personal Importation Scheme and may be seized and destroyed by Australian Border Force. |
| 10 June 2026 | TGA | Unapproved peptide products added as a compliance priority. |
| 19 June 2026 | Victorian Department of Health (Chief Health Officer Dr Caroline McElnay) | Six cases of acute liver injury in Victoria since January 2026 in people who used unapproved products labelled Retatrutide, also sold as "Reta", "R-10" and "R-20", bought online, through friends and via social media. Findings included raised liver enzymes (transaminases), with possible raised bilirubin and blood-clotting problems. "Additional contaminants may be contributing"; testing was underway. |
| 19 June 2026 | TGA and the Chief Medical Officer | National statement naming retatrutide alongside BPC-157, GHK-Cu, TB-500 and CJC-1295. TGA reports and state and territory hospitalisation data show liver damage, severe allergic reactions requiring hospitalisation, and inflammation. No numbers were published. |
| 20 July 2026 | TGA | Promoters and suppliers of unapproved peptides "put on notice". |
| 14 September 2026 | TGA | A person had uncontrollable vomiting and a torn oesophagus and needed hospital treatment. TGA testing found no retatrutide in the vial, only undeclared semaglutide at about 8 times the level in ARTG-registered semaglutide products. |
In August 2026 the ABC reported that at least seven Victorians had been seriously unwell with liver injury or failure. That is a media figure, not an official count. Victoria's alert says similar cases "may" have occurred elsewhere; no national count has been published.
Is retatrutide legal in Australia?
No product sold as retatrutide is on the ARTG, so all of them are unapproved therapeutic goods. The TGA says it is unlawful to import, advertise, manufacture and supply unapproved peptide products in Australia, and its guidance on importing, compounding and supplying unapproved peptides sets out the responsibilities involved.
Enforcement action in 2026 has included two large seizures. In April, a joint operation by Australian Border Force, the TGA and Victoria Police seized more than $2 million of steroids, performance and image enhancing drugs and peptides, and three people were charged. On 4 August, the TGA and NSW Police executed warrants at two NSW homes allegedly linked to a social media influencer who imported, relabelled and sold peptide and steroid products, seizing more than $120,000 of products including retatrutide.
Under the Therapeutic Goods Act 1989, maximum penalties include civil penalties of up to $1.82 million per breach for individuals and $18.2 million for corporations, and criminal penalties of up to 7 years' imprisonment. In the United States, Lilly has filed six lawsuits against sellers of products marketed as retatrutide, including research-use-only sellers, a medical spa and a compounding pharmacy.
Why are "research peptide" retatrutide products dangerous?
Because nobody outside the seller knows what is in the vial. The TGA puts it plainly: "Any retatrutide product accessed outside of clinical trials could be a counterfeit product."
The vial the TGA tested in September 2026 contained no retatrutide at all. It held semaglutide at about eight times the strength of registered products, and the person who used it was hospitalised.
Victoria's alert on liver injury says "additional contaminants may be contributing". Testing was still underway when the alert was issued, so the cause has not been confirmed.
No product sold as retatrutide has been through TGA evaluation. Calling it a "research peptide" does not change that: the TGA says supplying unapproved peptide products is unlawful.
The weight-loss and safety figures above come from Lilly's medicine, used under trial supervision. A product of unknown content and strength cannot be expected to behave the same way.
What can you do instead?
If you are thinking about medicine for weight, talk to a GP about the options that are registered in Australia. If you have already used a product sold as retatrutide, stop using it and tell a doctor.
Several GLP-1-based medicines are registered in Australia, including tirzepatide (Mounjaro), which the TGA approved for chronic weight management in September 2024. Whether any medicine suits you is a clinical decision that depends on your health history. Our guide to weight-loss medication in Australia and GLP-1 medicines in Australia explain what is registered and how access works, without recommending any of them.
If you have used a product labelled retatrutide, Reta, R-10 or R-20, Victoria's health department advises not to use it, to see a doctor about any symptoms, and to call the Poisons Information Centre on 13 11 26 for advice. Tell the doctor exactly what you took. In an emergency, call 000.
Retatrutide may one day reach regulators, but there is no confirmed Australian timeline. Until then, the only lawful access is as a participant in one of Lilly's clinical trials.
Is retatrutide approved in Australia?
No. As of 20 October 2026 the TGA states that retatrutide has not been approved by the TGA or any comparable international regulator. It is not on the ARTG, and Lilly says it is legally available only to participants in its clinical trials.
What is retatrutide?
Retatrutide (LY3437943) is an investigational medicine from Eli Lilly. It is a single peptide that activates three hormone receptors, GIP, GLP-1 and glucagon, and in trials it is given as a once-weekly injection. It is being studied for obesity, type 2 diabetes, knee osteoarthritis pain and sleep apnoea.
How much weight did people lose on retatrutide in trials?
In TRIUMPH-1, an 80-week trial in adults without diabetes, the 12 mg group lost an average of 28.3% of body weight under the efficacy estimand, or 25.0% regardless of whether people stopped treatment, compared with 2.2% and 3.9% on placebo. These are company-reported topline results.
Is it legal to get retatrutide in Australia?
No. Products sold as retatrutide are unapproved therapeutic goods. The TGA says it is unlawful to import, advertise, manufacture and supply unapproved peptide products in Australia, and imports identified only by codes, or without a clear active ingredient and strength, may be seized and destroyed.
When will retatrutide be available in Australia?
There is no confirmed date. The only filing plan Lilly has published is a US Biologics License Application in the first quarter of 2027. Any Australian approval date quoted online is speculation, and approval is never guaranteed.
What are Reta, R-10 and R-20?
They are names used for unapproved products labelled as retatrutide. The Victorian Department of Health linked products sold under these names to six cases of acute liver injury in Victoria between January and June 2026, and advised people not to use them.
Is retatrutide the same as Mounjaro?
No. Both are made by Eli Lilly, but Mounjaro contains tirzepatide, which activates two receptors (GIP and GLP-1) and is registered in Australia. Retatrutide adds a third receptor, glucagon, and is not approved anywhere.
Related explainers: Retatrutide side effects · Retatrutide vs tirzepatide · GLP-1 pills in Australia · Tirzepatide in Australia
Primary sources checked for this page.
- Jastreboff et al., "Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial", NEJM, published online 26 June 2023.
- Eli Lilly: TRIUMPH-4 topline, 11 December 2025.
- Eli Lilly: TRANSCEND-T2D-1 topline, 19 March 2026.
- Eli Lilly: TRIUMPH-1 topline, 21 May 2026.
- Eli Lilly: ADA results, TRIUMPH-1 sub-trials and TRANSCEND-T2D-1, 6 June 2026.
- Eli Lilly: TRIUMPH-2 and TRIUMPH-3 topline, 23 July 2026.
- Eli Lilly: TRIUMPH-2 detailed results (EASD and The Lancet), 29 September 2026.
- TGA safety alert: counterfeit retatrutide product, 14 September 2026.
- Victorian Department of Health: toxicity linked to unapproved peptide product labelled Retatrutide, 19 June 2026.
- TGA and Chief Medical Officer: public health risks of unapproved peptide products, 19 June 2026.
- TGA: risks of importing unapproved peptide products, 7 May 2026.
- TGA: compliance focus on unapproved peptide products, 10 June 2026.
- TGA: peptide promoters and suppliers put on notice, 20 July 2026.
- TGA: NSW seizure of peptides and steroids, 17 August 2026.
- TGA: ABF, TGA and Victoria Police seizure, 17 April 2026.
- TGA: understanding your responsibilities with unapproved peptide products (undated, retrieved 20 October 2026).
- ABC News: peptide tests and liver damage hospitalisations, 24 August 2026 (media report).
- Healio: Lilly lawsuits against six retatrutide sellers, 14 August 2026 (media report).
Editorial method: Australian regulator and state health department sources were checked first, peer-reviewed trial publications second, and company releases third. Lilly's topline results are company-reported and, unless a journal is named, not yet peer reviewed. Media figures are labelled as such. We do not publish approval dates, scheduling or case counts that no primary source confirms. Clinical review by a named Australian health professional is pending. See the Preptide editorial policy.
Important: General information only, not medical advice. Retatrutide is an investigational medicine of Eli Lilly that is not approved in Australia and is not lawfully available outside clinical trials; do not purchase or use products sold under its name. Mounjaro is a registered trademark of Eli Lilly. Preptide is independent and is not affiliated with, endorsed by or sponsored by Eli Lilly. Preptide is food, not medication, and does not prescribe, sell, recommend or promote prescription medicines. Talk to your doctor or pharmacist about any medicine. In an emergency call 000. Read our editorial policy and Health Acknowledgement.