The lines, side by side
Three documents set the rules a US prescriber works from: the FDA-approved label for the original brand, Glucophage, whose kidney wording a current generic label repeats with only the product name changed; the American Diabetes Association Standards of Care 2026; and the KDIGO 2022 guideline on diabetes in chronic kidney disease, which KDIGO says remains its current published diabetes guideline while a 2026 update is in development. All of them use eGFR in mL/min/1.73 m². They agree at the bottom line and differ in the band above it.
| eGFR | FDA label | ADA 2026 | KDIGO 2022 |
|---|---|---|---|
| 60 or above | Check eGFR before starting and at least once a year | May be used safely at 30 or above | Usual dosing; check kidney function at least once a year |
| 45 to 59 | No change in the label's renal section; this band falls inside the contrast-scan rule (30 to 60) | No separate rule stated | Same dose; consider a reduction with conditions that predispose to low blood flow or low oxygen; check every 3 to 6 months |
| 30 to 44 | Starting not recommended; if already taking it, assess benefit and risk of continuing | Do not start below 45; if already taking it, reduce the dose below 45 | Halve the maximum dose; if starting, begin at half the dose and go no higher than half the maximum; check every 3 to 6 months |
| Under 30 | Contraindicated; discontinue | Stop | Stop, and do not start; also stop when dialysis begins, whichever comes first |
The label's wording is exact. It contraindicates metformin "in patients with an estimated glomerular filtration rate (eGFR) below 30 mL/minute/1.73 m2", says "Initiation of GLUCOPHAGE/GLUCOPHAGE XR is not recommended in patients with eGFR between 30-45 mL/min/1.73 m2", and, for people already taking it whose eGFR "falls below 45", says to "assess the benefit and risk of continuing therapy." The generic label we checked on DailyMed, revised June 2026, carries the same three rules.
Where the three sources disagree
Starting metformin at an eGFR of 30 to 44. The label does not recommend it. The ADA is firmer: "metformin should not be started in those whose eGFR is <45 mL/min/1.73 m²." KDIGO points the other way. Its Recommendation 4.1.1, graded 1B, a strong recommendation, is to treat people with type 2 diabetes, chronic kidney disease and an eGFR of 30 or above with metformin, and its Figure 27 sends an eGFR of 30 to 44 down a separate path that reads "Initiate at half the dose and titrate upwards to half of maximum recommended dose." So a clinician following KDIGO and one following the label or the ADA can reach different answers for the same person, and each is following a published source.
Lowering the dose below 45. The label's renal section sets no reduced dose; it asks the prescriber to weigh benefit and risk. The ADA says the dose "should be reduced once eGFR is <45". KDIGO is the only one of the three that names an amount: it says the maximum dose should be halved once eGFR declines to 30 to 45.
The 45 to 59 band. Only KDIGO says anything specific here: keep the same dose, consider reducing it "in the presence of conditions that predispose patients to hypoperfusion and hypoxemia," and check eGFR every 3 to 6 months instead of once a year.
Why the cutoff is an eGFR, and why it moved
Older labels drew the line with creatinine alone. The Glucophage label posted by the FDA in 2008 listed as a contraindication "serum creatinine levels ≥1.5 mg/dL [males], ≥1.4 mg/dL [females] or abnormal creatinine clearance." The ADA's 2026 kidney section records that the FDA revised its guidance in 2016, "recommending use of eGFR instead of serum creatinine to guide treatment and expanding the pool of people with kidney disease for whom metformin treatment should be considered." (The FDA's 2016 safety communication page, which the ADA cites, returned a not-found page when we tried to open it on October 28, 2026, so we quote the label and the ADA rather than the communication.)
Because eGFR is calculated from creatinine, anything that moves creatinine without changing filtration can carry a reading across one of these lines. Some medicines do exactly that, and our guide to a high creatinine that is not kidney damage explains how to tell an artifact from a real decline. Age matters too: eGFR falls with age in people without kidney disease, which we cover in eGFR by age. Neither changes the metformin thresholds, which are the same at every age, but both are reasons to confirm a reading near 45 or 30 before a decision rests on it.
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What the lines protect against
The concern is lactic acidosis. The label states that metformin "is substantially excreted by the kidney, and the risk of metformin accumulation and lactic acidosis increases with the degree of renal impairment." The ADA puts the size of that risk in context: very high circulating levels, such as after an overdose or acute kidney injury, have been associated with lactic acidosis, "However, the occurrence of this complication is very rare" and it "primarily occurs when the estimated glomerular filtration rate (eGFR) is <30." For people at 30 to 45, the ADA adds, "there is an increased risk for periodic decreases of eGFR to ≤30," which is the reason that band carries caution even though the drug is allowed in it.
The label lists the other risk factors alongside kidney function: certain drugs (it names carbonic anhydrase inhibitors such as topiramate), age 65 or older, a radiological study with contrast, surgery and other procedures, hypoxic states such as acute congestive heart failure, excessive alcohol intake and hepatic impairment. That is why monitoring speeds up as kidney function falls. The label asks for an eGFR "at least annually in all patients" and more often in people at risk of declining kidney function, "e.g., the elderly"; KDIGO asks for every 3 to 6 months once eGFR is under 60.
Contrast scans and surgery
This rule reaches people whose eGFR is otherwise fine for metformin, because it applies up to an eGFR of 60. The label says to stop metformin "at the time of, or prior to, an iodinated contrast imaging procedure" in three groups:
- people with an eGFR between 30 and 60;
- people with a history of liver disease, alcoholism or heart failure;
- people who will be given intra-arterial iodinated contrast.
Then: "Re-evaluate eGFR 48 hours after the imaging procedure; restart" metformin "if renal function is stable." The label's patient leaflet describes these procedures as "x-ray tests with injectable dyes or contrast agents." On our reading, someone with an eGFR above 60 and none of the three listed conditions is outside the label's stop rule; the imaging team may still have its own protocol, so tell them you take metformin either way.
For surgery, the label's reason is fluid, not dye: withholding food and fluids "may increase the risk for volume depletion, hypotension, and renal impairment," so metformin "should be temporarily discontinued while patients have restricted food and fluid intake." When to stop and restart is for the surgical team to set.
What to do next
Find your band on our eGFR reference page, which carries the KDIGO categories with their source and date. The bands that touch metformin decisions each have their own page: G3a, 45 to 59, G3b, 30 to 44 and G4, 15 to 29. Enter your own result in the lab result lookup to see where it lands.
Long-term metformin has a second lab to keep track of. The label asks for vitamin B12 "at 2 to 3 year intervals", and KDIGO says to monitor for deficiency after more than 4 years of treatment; our vitamin B12 page has the ranges. For a full list of the tests that fit your age and history, build your personal screening plan.
Frequently asked questions
Can I keep taking metformin with an eGFR of 40?
The label allows it, with a benefit-and-risk review once eGFR is below 45. The ADA says the dose should be reduced below 45, and KDIGO says to halve the maximum dose at 30 to 45 and check eGFR every 3 to 6 months. Starting metformin fresh at 40 is where the sources split: the label does not recommend it, the ADA says not to, and KDIGO's dosing figure starts it at half the dose and goes no higher than half the maximum.
My eGFR came back at 28. Do I have to stop metformin?
The label tells prescribers to discontinue metformin when eGFR falls below 30, and every source here agrees. Whether one reading reflects a new baseline or a dip during an illness is your prescriber's call, so contact them promptly rather than waiting for the next routine visit. If you have symptoms the label lists for lactic acidosis, such as unusual muscle pain, trouble breathing, unusual sleepiness, stomach upset with vomiting, or a slow or irregular heartbeat, the label says to stop metformin and call your healthcare provider right away.
Do I need to stop metformin before a CT scan with contrast?
Under the label, yes if your eGFR is 30 to 60, if you have a history of liver disease, alcoholism or heart failure, or if the contrast will be injected into an artery. eGFR is then rechecked 48 hours after the scan and metformin restarted if kidney function is stable.
Does metformin damage the kidneys?
None of the sources here says it does. The ADA rates metformin's effect on chronic kidney disease progression as neutral and notes "there is no documented direct kidney benefit" either. The eGFR limits exist because the kidneys clear the drug, not because the drug harms them.
When to talk with a clinician
Raise it at your next visit if your eGFR has crossed 60, 45 or 30 since metformin was started, and sooner if it has fallen below 30. Before any scan or procedure, tell the team you take metformin and ask for your most recent eGFR. If you are being started on metformin with an eGFR under 45, it is fair to ask which guideline the dose follows, because the label, the ADA and KDIGO do not agree on that case.
