The FLOW Trial: Semaglutide for Kidney Disease Explained

Semaglutide is a GLP-1 receptor agonist sold as Ozempic (up to 2.0 mg weekly, approved for type 2 diabetes) and Wegovy (2.4 mg weekly, approved for chronic weight management), both given as a subcutaneous injection. The FLOW trial used the 1.0 mg Ozempic dose. It is a different question from "does semaglutide cause weight loss" (the STEP trials) or "does semaglutide reduce cardiovascular events in obesity without diabetes" (SELECT). This article treats FLOW as answering a narrower, more specific question: does adding semaglutide to standard kidney-protective medication slow progression to kidney failure in people who already have type 2 diabetes and significant diabetic kidney disease.

The core answer, and its boundary

FLOW enrolled adults with type 2 diabetes, an estimated glomerular filtration rate (eGFR) of roughly 50 to 75 mL/min/1.73 m², and a urinary albumin-to-creatinine ratio (UACR) above 300 mg/g, all already on the maximum blood pressure medication they could tolerate. In that specific population, semaglutide 1.0 mg weekly reduced the combined risk of a major decline in kidney function, kidney failure, or kidney- or cardiovascular-related death, and the trial was stopped earlier than planned because the benefit crossed a prespecified statistical threshold. This finding does not establish that semaglutide protects the kidneys of people without diabetes, people with only mild albuminuria, or people with more advanced kidney failure, and it does not by itself constitute an FDA-approved kidney disease indication as of this writing. The exact hazard ratio and confidence interval reported in the original New England Journal of Medicine publication (Perkovic et al., 2024) should be verified by the reviewing clinician against the primary paper before being quoted as a fixed number in patient-facing material.

What FLOW actually tested

The trial enrolled 3,533 adults across many countries, all with type 2 diabetes and at least stage 3 chronic kidney disease, defined by the eGFR and UACR criteria above. Everyone was already on renin-angiotensin-aldosterone system (RAAS) blockade at the highest dose they could tolerate, meaning any benefit from semaglutide was measured on top of, not instead of, current standard nephroprotective care.

An independent data monitoring committee stopped the trial ahead of schedule because the prespecified kidney-outcome benefit had already been demonstrated. Trials stopped early for efficacy can sometimes overstate the true effect size in the interim analysis, which is a reason to treat the topline percentage as a strong but early signal rather than a final, precise number.

The trial also reported fewer cardiovascular deaths in the semaglutide group and modest weight loss compared with placebo. Because the weight loss in FLOW was smaller than what is typically seen in the higher-dose weight management trials, some researchers have argued the kidney benefit may be at least partly independent of weight loss magnitude, though the underlying mechanism has not been established. A newer prespecified pooled analysis across semaglutide's cardiovascular and renal outcome trials (SELECT, FLOW, and the oral semaglutide cardiovascular trial SOUL) examined kidney-related endpoints across programs; editors should confirm the specific comparative findings against that paper before citing exact figures (pooled analysis, 2026). Separately, mechanistic work using tissue-level methods is underway to characterize how semaglutide affects kidney tissue directly, independent of weight change; this line of research is described as exploratory and has not yet produced a settled mechanism (REMODEL mechanistic program, 2026).

How FLOW differs from the STEP, SELECT, and SURMOUNT trials

Semaglutide has separate phase 3 outcome trials for three different clinical questions, and mixing them up leads to overclaiming:

• STEP-1, STEP-2, STEP-3, STEP-5 (semaglutide 2.4 mg, Wegovy dose) measured body weight change over 68 to 104 weeks in adults with obesity, with and without type 2 diabetes, with and without added behavioral therapy. These trials support Wegovy's weight management indication. They did not enroll people selected for chronic kidney disease and did not measure kidney failure as an outcome.
• SELECT (semaglutide 2.4 mg) measured major cardiovascular events in adults with overweight or obesity and established cardiovascular disease, without diabetes. It supports a cardiovascular risk reduction claim in that population.
• FLOW (semaglutide 1.0 mg, the Ozempic diabetes dose) measured kidney disease progression in adults who already had type 2 diabetes and significant diabetic kidney disease.
• SURMOUNT-1, SURMOUNT-2, SURMOUNT-4 are tirzepatide (a dual GIP/GLP-1 agonist, brand names Zepbound and Mounjaro) trials measuring weight loss and weight maintenance. Tirzepatide does not yet have a completed phase 3 trial with kidney failure as a primary outcome.

Because these trials used different doses, different formulations, different comparator populations, and different primary endpoints, a reader should not assume that a result from one trial (for example, STEP-1's weight loss percentage) applies to a different population (for example, people with stage 3 CKD in FLOW).

Decision framework: is a given patient inside the FLOW evidence, or outside it?

This is not a treatment algorithm and does not replace an individualized medical evaluation. It is a way to check whether a specific clinical situation actually matches what FLOW tested, versus a situation where the FLOW result is being extrapolated beyond its evidence.

Next steps if a patient falls inside the FLOW criteria: confirm RAAS blockade is already optimized, check baseline eGFR and UACR, use a gradual dose escalation, and recheck eGFR and UACR periodically (a reasonable interval discussed in obesity and diabetes care guidance is roughly every three months during the first year, though the exact cadence should follow the treating clinician's judgment and local guideline). If a patient falls outside the criteria (no diabetes, mild albuminuria, or eGFR outside the studied range), semaglutide may still be reasonable for other indications, but calling it "kidney protection" for that specific patient is extrapolation beyond FLOW's evidence and should be described to the patient as such.

Regulatory status and what "off-label" means here

Semaglutide 1.0 mg (Ozempic) is FDA-approved for the management of type 2 diabetes. FLOW's results support using semaglutide within that existing type 2 diabetes indication in patients who also have chronic kidney disease, since the FDA-approved use already covers this population's underlying diagnosis. As of this writing, semaglutide does not carry a separate, standalone FDA-approved indication specifically for chronic kidney disease. Readers and clinicians should check the current FDA label directly, since indications and labeling can change, at the FDA's own drug information pages rather than relying on a cached PDF link (drug label status should always be verified against Drugs@FDA for the current date). Wegovy, the 2.4 mg weight management formulation, is a separate product with a separate approved indication and was not the dose studied in FLOW.

Safety considerations specific to chronic kidney disease

Three points are worth stating plainly rather than folding into a general safety list.

First, semaglutide is not cleared by the kidneys, which is one practical reason it is used across a range of kidney function without the dose adjustments required for some other diabetes medications. This is consistent with its general pharmacology, though any individual dosing decision at advanced kidney impairment should follow the current FDA label and the treating clinician's judgment, since FLOW itself excluded patients with very low eGFR.

Second, the main acute risk in this population is not a kidney-specific drug toxicity but dehydration from nausea or vomiting during dose escalation, which can transiently worsen kidney function in someone who already has reduced kidney reserve. Gradual titration and clear guidance to patients about fluid intake and when to pause escalation if GI symptoms are severe are standard practice, not unique to this trial.

Third, diabetic retinopathy has been reported as a signal of interest in some semaglutide trials in people with type 2 diabetes; routine ophthalmologic monitoring already recommended for people with diabetes remains appropriate and is not something FLOW changes.

Semaglutide versus tirzepatide for kidney disease specifically

Tirzepatide has shown larger average weight loss than semaglutide in head-to-head-adjacent trial comparisons, and it has a discontinuation trial (SURMOUNT-4) showing that stopping the drug leads to substantial weight regain, a pattern that likely generalizes to semaglutide as well: these are chronic therapies, and their benefits should be expected to wane after discontinuation. However, no completed phase 3 tirzepatide trial has kidney failure as a primary, prespecified outcome the way FLOW does for semaglutide. A clinician choosing between the two agents for a patient with type 2 diabetes and chronic kidney disease is weighing a larger, but kidney-outcome-unproven, weight-loss effect against a smaller, but directly kidney-outcome-proven, semaglutide effect. Neither choice is self-evidently correct; it depends on the patient's priority (weight loss magnitude versus documented renal outcome evidence) and on other individual factors that a specific evidence page like this one cannot resolve.

Evidence boundary: what is established, what is plausible, what is not established

Established: In a specific trial population, adults with type 2 diabetes, eGFR roughly 50 to 75, and macroalbuminuria, already on maximum RAAS blockade, adding semaglutide 1.0 mg weekly reduced a composite kidney and cardiovascular death outcome compared with placebo, and the trial was stopped early for efficacy.

Plausible but unproven: That the mechanism is partly independent of weight loss; that the FLOW benefit generalizes to people with milder albuminuria, no diabetes, or eGFR outside the studied range; that similar benefit would be seen with tirzepatide or other GLP-1 or dual agonists.

Not established: A standalone FDA-approved kidney disease indication for semaglutide; a head-to-head kidney outcomes comparison between semaglutide and tirzepatide; long-term (beyond the trial's follow-up) durability of the kidney benefit after treatment is stopped.

When to seek urgent care rather than wait for a routine follow-up

Persistent vomiting, inability to keep fluids down, signs of dehydration (dizziness, very dark urine, markedly reduced urination), or a sudden drop in urine output in someone with known chronic kidney disease on semaglutide warrants prompt medical evaluation rather than waiting for a scheduled lab check. This is general safety guidance for anyone with reduced kidney reserve on a GLP-1 agent, not a FLOW-specific finding.