Retatrutide and the liver and kidneys

Two very different stories share the word "liver". In the trials, retatrutide reduced liver fat dramatically and caused only rare, short-lived changes in liver blood tests. In Australia in 2026, people using unlicensed products labelled retatrutide developed acute liver injury, with a contaminant suspected. Keeping those two apart is the whole point of this page. For the kidneys, the risk is simpler: severe vomiting or diarrhoea can dehydrate you enough to injure them.

The liver in the trials

ALT is an enzyme that leaks into the blood when liver cells are damaged, so it is the standard blood test for liver injury. In the 48-week Phase 2 trial, about 1% of people on retatrutide had a rise in ALT to more than three times the upper limit of normal, and these rises were transient.^[1] That is the kind of finding that trial doctors watch and repeat, rather than a signal of serious hepatotoxicity. Lilly's Phase 3 announcements have not reported liver-test data; the full papers will.

Meanwhile, the liver was one of the places retatrutide showed the clearest benefit. A sub-study of the Phase 2 trial enrolled 98 people with MASLD (fatty liver disease) and liver fat of at least 10%. After 24 weeks, liver fat had fallen by 42.9%, 57.0%, 81.4% and 82.4% on the four doses, against a 0.3% rise on placebo, and 86% of people on the highest dose reached a normal liver fat level.^[2] Retatrutide's third target, the glucagon receptor, is thought to be part of why it clears liver fat so effectively.^[2]

So the trial drug, given at a known dose to people with healthy or fatty livers, was on balance good for the liver.

The liver injuries were not the trial drug

On 19 June 2026 the Victorian Department of Health issued a health alert after six cases of acute liver toxicity since January in people using an unapproved peptide product labelled Retatrutide. The alert said the clinical picture suggested additional contaminants may be contributing, and that all such products were at risk.^[3] Further cases have been reported since.

ABC News reported the cases in detail: a 32-year-old woman in Melbourne developed acute liver failure within a week of two doses, spent about a month in hospital, and came close to needing a transplant; two women in their 20s were treated for liver injury; and a hepatologist involved said, of the products, that nobody knew what they were.^[5]

The distinction is crisp:

• The trial drug reduced liver fat and produced rare, transient enzyme rises.^[1][2]
• The injuries occurred in people using unlicensed products of unknown composition, with a suspected contaminant.^[3]

That does not make retatrutide innocent by default. Nobody has proved what caused the injuries, and the liver enzyme rises in the trial show the drug can touch the liver. But it means a product that has never been tested cannot be judged by trial data, in either direction. The full account is on the liver-failure cluster page, and testing of what vials actually contain is on what is actually in the vials.

The kidneys: it is about fluid

Retatrutide is not known to be directly toxic to the kidneys. The risk is indirect. Vomiting and diarrhoea are its most common side effects, covered on the gut effects page, and both drain water and salts. The Mounjaro SmPC warns that these reactions may lead to dehydration, which could cause a deterioration in kidney function including acute kidney failure, and that older people are more susceptible; the Wegovy SmPC carries the same warning.^[4][6]

The Australian reporting shows the extreme end. A man in his 40s developed major kidney injury from extreme dehydration after having diarrhoea about 40 times a day on a product labelled retatrutide.^[5] A Melbourne gastroenterologist described another young man losing an estimated eight litres of fluid a day and needing intravenous rehydration in hospital.^[7] Neither man had a clinician checking on him until he was already seriously ill. In a trial, someone would have.

The NHS lists the warning signs of dehydration as thirst, headache, dizziness, dark strong-smelling urine, passing urine less often, tiredness and a dry mouth, and says to get urgent help if you are unusually tired, dizzy on standing, or passing very little urine.^[8]

People with existing kidney or liver disease

The Phase 2 trial excluded anyone with an eGFR (a measure of kidney function) below 45, and anyone with liver disease other than fatty liver.^[9] So the trial safety data come from people whose kidneys and livers were working reasonably well.

Lilly is now running TRANSCEND-T2D-3, a Phase 3 trial of retatrutide in people with type 2 diabetes and moderate or severe kidney impairment who are on insulin; it is expected to finish in late 2026.^[10] Until it reports, there is no evidence on retatrutide in people with significant kidney disease, and none at all in significant liver disease. This is on the what we do not know yet list.

Trial product versus what is sold online

Every reassuring number on this page comes from a pharmaceutical-grade product at a known dose. Every alarming case comes from an unlicensed product of unknown strength and purity. A clinician in a trial would adjust treatment; outside a trial there is no clinician and no known dose. Unlicensed products carry the drug's own risks plus unknown extra ones, and the liver-injury cluster is the clearest example yet of what "unknown" can mean.