Quick answer: retatrutide kidney data so far come mainly from an analysis of two phase 2 trials. Higher doses lowered urine albumin (protein in the urine, a sign of kidney stress) by about 28% to 37% versus placebo, and estimated kidney filtration was unchanged in people with diabetes and higher in people with obesity.[1] These were short trials in people with mostly healthy kidneys. Dedicated kidney trials are still running, and retatrutide is not FDA-approved.
This page explains those results, what they can and cannot tell you, and what the ongoing trials will add. For an overview of the drug, see the retatrutide profile.
Two kidney measures, explained
Kidney studies mostly track two numbers:
- eGFR (estimated glomerular filtration rate): an estimate of how well the kidneys filter blood, calculated from blood levels of creatinine, cystatin C or both. Higher is generally better.
- UACR (urine albumin-to-creatinine ratio): how much albumin, a protein, leaks into the urine. A lower number usually means less kidney stress.
Creatinine comes mainly from muscle, and cystatin C partly from fat tissue, so large weight loss can shift these estimates without a real change in filtration.[1] Keep that in mind when reading eGFR results.
What the phase 2 kidney analysis found
Researchers looked back at kidney data from the 36-week type 2 diabetes trial (281 people) and the 48-week obesity trial (338 people). Most participants had normal kidney function, with average eGFR around 90 and only about 5% to 6% below 60.[1]
| Measure | Type 2 diabetes trial (12 mg vs placebo) | Obesity trial (12 mg vs placebo) |
|---|---|---|
| Urine albumin (UACR) | −37.0% | −31.5% |
| eGFR (creatinine-based) | No difference at 36 weeks | +8.5 mL/min/1.73 m² |
| Systolic blood pressure | −12.2 mmHg | −10.5 mmHg |
Source: Heerspink et al., Kidney International Reports 2025.[1]
Other findings from the same analysis:[1]
- On 8 mg in the obesity trial, UACR fell 28.0% and eGFR rose 5.3 units.
- In the diabetes trial, 12 mg lowered UACR 32.2% more than dulaglutide, a GLP-1 drug.
- eGFR first dipped around week 12 on retatrutide, a pattern also seen with GLP-1 and tirzepatide-type drugs, then recovered.
- In the obesity trial, the eGFR rise had mostly disappeared 4 weeks after stopping the drug.
What these results mean
A 30% or greater fall in albuminuria has been linked, in other treatments, to a lower chance of kidney disease getting worse. The authors noted the drop seen with retatrutide in diabetes was in that range.[1]
But they also listed clear limits:[1]
- It was a post hoc analysis, done after the trials ended, without adjustment for multiple comparisons.
- Few participants had kidney disease, and most had normal albumin levels, so the absolute changes were small.
- The trials were too short for any kidney outcomes, such as kidney failure, to occur.
- The researchers called the results hypothesis-generating.
The rise in eGFR in the obesity trial is unusual. The authors said they knew of no other drug with this pattern, and its cause is not understood.[1] It does not yet mean the kidneys are working better in a lasting way.
The authors also suggested that eGFR based on cystatin C may be the better way to track kidney function on retatrutide. In the obesity trial, weight changes tracked with creatinine-based eGFR but not with the cystatin C version, so weight loss itself could be skewing the creatinine estimate.[1]
Kidney safety signals in the trials
The same analysis reviewed kidney-related side effects:[1]
- Acute kidney injury: one serious case on retatrutide 8 mg in the obesity trial, considered possibly related to a COVID-19 infection, and one serious case on placebo in the diabetes trial.
- Other kidney events: one mild kidney impairment report on 12 mg in the diabetes trial. In the obesity trial, three reports of chronic kidney disease or kidney failure, two on retatrutide and one on placebo.
- Dehydration: four people in the obesity trial (three on retatrutide), and one moderate case on 8 mg in the diabetes trial.
- Electrolytes: no clinically significant changes in either trial.
Vomiting and diarrhea are common with retatrutide, especially at higher doses. Severe or prolonged fluid loss can strain the kidneys, which is why staying hydrated matters. See retatrutide side effects for rates by dose.
Kidney stones and urinary infections
We found no mention of kidney stones among the side effects in the published retatrutide trial summaries or Lilly’s releases. Urinary tract infections were somewhat more common than on placebo in TRIUMPH-1: 7.5%, 8.8% and 8.4% on 4, 9 and 12 mg, versus 5.3%. Lilly said most were mild to moderate.[8]
In a study of people describing their own use of unapproved retatrutide online, 1.8% mentioned kidney or urinary problems of any kind, a figure that cannot show cause.[9]
Trials testing retatrutide in kidney disease
| Trial | Who | Main measure | Status |
|---|---|---|---|
| TRANSCEND-CKD (phase 2b) | 146 adults with obesity and CKD | Measured GFR at 24 weeks | Completed Oct 2025; results not yet published |
| TRANSCEND-T2D-3 (phase 3) | about 320 adults with diabetes and moderate or severe kidney impairment, on insulin | HbA1c at 52 weeks | Primary completion estimated Oct 2026 |
| TRIUMPH-Outcomes (phase 3) | about 10,000 adults with heart disease and/or CKD | Heart and kidney events | Primary completion estimated Feb 2029 |
Sources: TRANSCEND-CKD,[2][3] TRANSCEND-T2D-3,[5][7] TRIUMPH-Outcomes.[4]
TRANSCEND-CKD is the most direct test. It measures kidney filtration with an injected tracer (iohexol) rather than estimating it from blood tests, and uses MRI to look at kidney blood flow and fat around the kidneys. Its participants had an average measured GFR of 49, meaning moderately reduced kidney function.[2]
TRIUMPH-Outcomes includes a kidney composite endpoint: kidney failure, a sustained drop in eGFR of 40% or more, or death from kidney or heart causes.[4]
Lilly has also completed a small study of how the body handles a single dose of retatrutide in people with severe kidney impairment or end-stage kidney disease. No results had been posted as of October 2026.[6]
For how an approved drug in this class has been studied in kidney disease, see Ozempic and kidney disease.
Questions to ask a clinician
- What are my eGFR and urine albumin results, and how often should they be checked?
- Which approved medicines protect the kidneys in someone like me?
- How should I manage fluids if a weight-loss drug causes vomiting or diarrhea?
- Would I qualify for a retatrutide kidney trial?
For the bigger safety picture, see is retatrutide safe?, and for blood pressure, which also affects the kidneys, see retatrutide blood pressure and heart rate.
