GLP-1s and Kidney Health: What the FLOW Trial Found

FLOW (Evaluate Renal Function with Semaglutide Once Weekly) was a large, randomized, placebo-controlled trial designed specifically to test whether semaglutide could protect the kidneys in people with type 2 diabetes and chronic kidney disease (CKD) — a combination that affects roughly 1 in 3 adults with diabetes and is a leading cause of dialysis and kidney transplant. Published in the New England Journal of Medicine in 2024 (Perkovic et al.), the trial enrolled 3,533 participants across 28 countries and followed them for a median of over 3 years. It matters because, until FLOW, GLP-1 kidney benefits were mostly inferred as a side effect noticed in diabetes and cardiovascular trials like SUSTAIN-6 and SELECT — FLOW was the first trial built from the ground up to answer the kidney question directly, with kidney failure and kidney-related death as the primary outcome, not an afterthought.

Semaglutide reduced the risk of the trial's primary composite outcome — a combination of kidney failure, a sustained 50% or greater drop in kidney filtration rate (eGFR), or death from kidney or cardiovascular causes — by 24% compared with placebo. The result was strong enough that the trial's independent data monitoring committee recommended stopping it roughly a year ahead of schedule in late 2023, because continuing would have meant denying an established benefit to the placebo group. Participants on semaglutide also showed a slower rate of eGFR decline over time and fewer cardiovascular events, consistent with earlier trials like [GLP-1s and Fatty Liver: What ESSENCE Found](/blog/glp1-fatty-liver-mash-essence-trial-results), which similarly showed organ-level benefits beyond the scale. Based on FLOW, the FDA approved a new indication for Ozempic in 2025 specifically to reduce the risk of kidney disease worsening, kidney failure, and cardiovascular death in adults with type 2 diabetes and CKD.

The exact mechanism is still being studied, but researchers believe it's a combination of several effects working together, not just better blood sugar control. GLP-1 receptors are present in the kidney itself, and animal and mechanistic studies suggest semaglutide reduces inflammation and oxidative stress within kidney tissue, lowers the pressure inside the kidney's filtering units (glomeruli), and improves blood vessel function. Weight loss and modest blood pressure reduction likely contribute too, but statistical analyses of FLOW suggest the kidney benefit was only partly explained by changes in blood sugar, weight, and blood pressure — meaning something more direct is happening. This 'more than the sum of its parts' pattern has shown up elsewhere too, including in [GLP-1s and sleep apnea](/blog/glp1-sleep-apnea-surmount-osa-tirzepatide-results), where breathing improvements also outpaced what weight loss alone would predict.

FLOW specifically enrolled adults with type 2 diabetes who also had chronic kidney disease, defined by specific ranges of eGFR and urine albumin levels — this was not a general population or a weight-loss-only population. If you have type 2 diabetes and any degree of reduced kidney function, this trial is directly relevant to a conversation with your doctor, even if weight loss isn't your main goal. If you don't have diabetes, or you're taking a GLP-1 purely for weight management with normal kidney function, FLOW doesn't tell us your kidney risk changes one way or another — that population wasn't studied here. It's also worth noting FLOW tested semaglutide specifically; tirzepatide hasn't had an equivalent dedicated kidney outcomes trial published as of this writing, so we can't yet say whether the dual GIP/GLP-1 mechanism produces the same effect.

Ask specifically whether your current eGFR and urine albumin-to-creatinine ratio (uACR) fall into the range studied in FLOW, and whether a GLP-1 could be added to or replace part of your current regimen with kidney protection as an explicit goal, not just blood sugar control. Bring up how this fits alongside other kidney-protective medications you may already be on, like SGLT2 inhibitors, since many people with diabetic kidney disease end up on both classes together based on trial evidence. If you're managing diabetes, menopause, and weight simultaneously, kidney function is also worth tracking alongside the [heart-related tests worth asking for in menopause](/blog/apob-and-lipoprotein-a-in-menopause-tests-to-ask-for), since cardiovascular and kidney risk tend to move together as estrogen declines.