Does Retatrutide Affect Kidney Function? The Short Answer

The main kidney data for retatrutide come from a 2025 analysis of its two Phase 2 trials, one in adults with type 2 diabetes and one in adults with obesity without diabetes. Over 36 and 48 weeks, the higher doses were associated with less protein in the urine, and in the obesity trial with a higher estimated glomerular filtration rate (eGFR), the standard estimate of how well the kidneys filter blood:

• Albuminuria: on 12 mg, the urine albumin-to-creatinine ratio (UACR) fell by 37.0% compared with placebo in type 2 diabetes and by 31.5% in obesity.
• eGFR in obesity: after an initial dip, eGFR rose with the dose, ending 8.5 ml/min per 1.73 m² above placebo on 12 mg at 48 weeks (creatinine-based).
• eGFR in type 2 diabetes: after a similar early dip, eGFR returned to baseline and did not differ from placebo at 36 weeks.

The authors call the analysis exploratory and hypothesis-generating. Neither trial was designed to study the kidneys, people with an eGFR below 45 were excluded, and the authors note that the treatment periods were too short for kidney outcome events of the kind counted in dedicated kidney trials to occur. Whether retatrutide protects the kidneys over the long term is not known.

Where the Retatrutide Kidney Data Come From

The analysis was published online in Kidney International Reports in April 2025 by Hiddo Heerspink of the University Medical Center Groningen and six co-authors from Eli Lilly, which funded the study and was involved in its design, analysis and writing. It reused data from two randomized, placebo-controlled Phase 2 trials run in the United States:

• Type 2 diabetes trial: 281 adults, 36 weeks, retatrutide 0.5 mg to 12 mg, with dulaglutide 1.5 mg as an active comparator.
• Obesity trial: 338 adults with obesity or overweight and no diabetes, 48 weeks, retatrutide 1 mg to 12 mg.

Most participants had normal kidney function at the start. Mean creatinine-based eGFR was 91 ml/min per 1.73 m² in the diabetes trial and 90 in the obesity trial, and median UACR was 13 and 7 mg/g. Only 23% and 10% had a UACR of 30 mg/g or more, the level the authors class as micro- or macroalbuminuria. The analysis used the efficacy estimand, which leaves out data collected after participants permanently stopped the study drug; how this differs from other ways of counting is explained in why retatrutide weight loss numbers differ. The blood sugar results of the diabetes trial are covered in retatrutide for diabetes.

Retatrutide and Albuminuria (UACR)

Albuminuria, the leakage of the protein albumin into the urine, is an early marker of kidney damage. The changes below compare each retatrutide dose with placebo at the end of treatment.

In the diabetes trial, UACR stayed stable on placebo and did not change on dulaglutide compared with placebo, so retatrutide 12 mg also reduced it by 32.2% more than dulaglutide. In the obesity trial, UACR rose on placebo but was lower on retatrutide 8 mg and 12 mg than on placebo. In the diabetes trial the largest reduction was on 12 mg; for the obesity trial, the paper reports the reductions on 8 mg and 12 mg.

Among participants who started with a UACR of 30 mg/g or more, the reductions looked larger, but the subgroups were small (62 and 33 people) and the differences from placebo were not statistically significant. In the diabetes subgroup, 12 mg was associated with a 48.4% reduction; in the obesity subgroup, the estimates were 71.1% on 8 mg and 3.7% on 12 mg, with very wide confidence intervals.

The authors note that because most participants had normal albuminuria, the absolute reduction was modest. They also describe the reduction in type 2 diabetes as potentially clinically relevant, because treatments that lower albuminuria by more than 30% have been associated with a lower risk of clinical kidney outcomes in previous trials. That link has not been tested for retatrutide.

Retatrutide and eGFR: A Dip, Then a Rise

eGFR was estimated three ways: from creatinine, from cystatin C, and from both combined. Both trials showed an early drop in creatinine-based eGFR at week 12, but what happened next differed.

• Type 2 diabetes: the week-12 drop was statistically significant compared with placebo on 8 mg and 12 mg. After that, eGFR returned to baseline, and there were no differences from placebo at weeks 24 and 36. Cystatin C–based and combined eGFR did not differ from placebo at any point.
• Obesity: eGFR dropped at week 12 in all groups, including placebo. After that it rose with the dose on retatrutide and stayed flat on placebo. The authors write that eGFR ended 5 to 10 ml/min per 1.73 m² above baseline with creatinine and 10 to 15 with cystatin C, and that the increase was mostly reversed 4 weeks after the drug was stopped.

The early dip is consistent with the transient eGFR decreases seen with other GLP-1 and GIP/GLP-1 drugs, according to the authors. The full pattern, an early dip followed by a rise above baseline, has not been observed with any other drug, to their knowledge. Because it came with lower albuminuria, they suggest the higher filtration was accompanied by lower pressure inside the kidney's filtering units, but the mechanism is not established.

Why Weight Loss Complicates eGFR Results

eGFR is calculated from blood markers, not measured directly, and both markers can be affected by changes in body composition. As the authors explain, creatinine comes mainly from skeletal muscle, so losing muscle can lower it and make eGFR look higher without a real change in filtration, and cystatin C is mainly produced in fat tissue, so losing fat could affect it too. With retatrutide producing large weight loss, both effects are plausible.

The authors looked for this. In the obesity trial, weight change correlated with creatinine-based and combined eGFR, but not with cystatin C–based eGFR; in the diabetes trial, there was no consistent link. During the 4-week washout, body weight rose by 2.5% and 3.2% in the 8 mg and 12 mg groups while eGFR moved back toward baseline, which the authors read as a drug effect unrelated to body mass. On that basis, they suggest that cystatin C–based eGFR is the preferred method for monitoring eGFR during retatrutide treatment. A directly measured GFR, using the tracer iohexol, is the subject of a dedicated trial with no published results yet (see below). How retatrutide affects muscle is covered in retatrutide muscle loss.

Blood Pressure and Kidney Changes

Retatrutide lowered blood pressure in a dose-dependent way in both trials, which could in principle help explain lower albuminuria. On 12 mg, systolic pressure fell by 12.2 mm Hg compared with placebo at 36 weeks in type 2 diabetes and by 10.5 mm Hg at 48 weeks in obesity; dulaglutide did not lower blood pressure. In the obesity trial, at least one blood pressure medicine was stopped in 41% and 30% of participants on 8 mg and 12 mg.

However, changes in blood pressure and in UACR were not consistently correlated, and neither were changes in UACR and eGFR. The authors conclude that lower blood pressure is unlikely to explain the albuminuria reduction, and that weight loss, lower HbA1c and direct effects through GIP and glucagon receptors in the kidney may also contribute. These remain hypotheses. The wider blood pressure data are covered in retatrutide and blood pressure.

Kidney Safety in the Retatrutide Trials

Kidney-related adverse events were rare in the trials reported so far:

• Phase 2, type 2 diabetes: one serious adverse event of acute kidney injury, in the placebo group; one participant on 12 mg had mild kidney impairment and one on 8 mg had moderate dehydration.
• Phase 2, obesity: one serious event of acute kidney injury on 8 mg, considered possibly secondary to a COVID-19 infection, and three other events of chronic kidney disease or kidney failure, one on placebo and two on retatrutide. Dehydration was reported in 3 participants on retatrutide and 1 on placebo.
• TRIUMPH-1 (Phase 3, 80 weeks): severe or serious acute kidney events occurred in 2 participants (0.3%) on 4 mg, none on 9 mg, 2 (0.3%) on 12 mg and none on placebo, among 2,335 participants in the safety analysis.

The Phase 2 analysis found no clinically significant changes in blood electrolytes. Hypotension or orthostatic hypotension was reported in 4 participants in the diabetes trial, all on retatrutide, and in 8 participants on retatrutide against 1 on placebo in the obesity trial.

For approved drugs in the same class, the US labels of tirzepatide and semaglutide warn about acute kidney injury due to fluid loss, mostly in people whose nausea, vomiting or diarrhea led to dehydration. Retatrutide causes the same gastrointestinal side effects, which are covered in retatrutide side effects; urinary tract infections, which were more common on retatrutide than on placebo in TRIUMPH-1, are covered in retatrutide and urinary tract infections.

Retatrutide vs Semaglutide and Tirzepatide on the Kidneys

Lower albuminuria is not unique to retatrutide. In their discussion, the authors cite sustained reductions in people with chronic kidney disease (CKD) and type 2 diabetes on semaglutide and dulaglutide, a 52% reduction with semaglutide 2.4 mg in people with CKD without diabetes, and lower albuminuria with tirzepatide in people with type 2 diabetes or obesity. They also note that semaglutide reduced the risk of a composite kidney end point in a dedicated kidney outcome trial.

That is the main difference in the evidence: semaglutide has kidney outcome data, while retatrutide has a post hoc analysis of biomarkers in people who mostly had healthy kidneys. The only direct comparison, against dulaglutide in the diabetes trial, favored retatrutide 12 mg for UACR. These are not head-to-head comparisons with semaglutide or tirzepatide.

What Is Still Unknown About Retatrutide and the Kidneys

• Effects in people with kidney disease. Only 5.9% and 5.3% of participants had an eGFR below 60, and anyone below 45 was excluded.
• Measured, not estimated, filtration. A Phase 2 trial of retatrutide on kidney function in people with overweight or obesity and CKD (NCT05936151) is described in the 2025 paper as using iohexol to measure GFR directly. Lilly's listing gives an enrollment goal of 146, dates from July 2023 to October 2025 and completed enrollment, and shows no results.
• Long-term kidney outcomes. TRIUMPH-Outcomes (NCT06383390), a Phase 3 trial with an enrollment goal of 10,000, is testing whether retatrutide lowers cardiovascular events or prevents worsening kidney function; the listing runs to February 2029. Retatrutide's longer-term safety is covered in retatrutide long-term safety.
• Kidney data from Phase 3. The published TRIUMPH-1 paper reports kidney adverse events but not eGFR or albuminuria.

Retatrutide Sold Online: Why the Trial Data Don't Apply

Retatrutide is not approved and, according to its developer, is legally available only through clinical trials; its regulatory position is tracked in retatrutide approval status. The company says anything sold to consumers outside those trials is illegal, and warns that illicit retatrutide products may contain "unknown ingredients, harmful contaminants and impurities." The kidney findings above come from trials that excluded people with reduced kidney function and monitored participants closely.

Sources

• Heerspink HJL, Lu Z, Du Y, et al. The Effect of Retatrutide on Kidney Parameters in Participants With Type 2 Diabetes Mellitus and/or Obesity. Kidney Int Rep. 2025;10:1980–1992. DOI: 10.1016/j.ekir.2025.03.049.
• Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med. Published September 29, 2026. DOI: 10.1056/NEJMoa2604169. (TRIUMPH-1)
• Lilly Trials. A Study of Retatrutide (LY3437943) on Renal Function in Participants With Overweight or Obesity and Chronic Kidney Disease With or Without Type 2 Diabetes. NCT05936151, trial listing.
• Lilly Trials. The Effect of Retatrutide Once Weekly on Cardiovascular Outcomes and Kidney Outcomes in Adults (TRIUMPH-Outcomes). NCT06383390, trial listing.
• Eli Lilly. What to know about retatrutide. Last updated September 2026.
• Eli Lilly. US prescribing information for tirzepatide for weight reduction, section 5.3. Revised August 2026.
• Novo Nordisk. US prescribing information for semaglutide injection and tablets for weight reduction, section 5.5. Revised June 2026.

Medical Disclaimer: This article is for informational purposes only and is not medical advice. Retatrutide is investigational and is not approved by the FDA for any use. It is not available by prescription, and Lilly says anything sold to consumers under its name outside its clinical trials is illegal. The figures described here are those reported in clinical trials under medical supervision.