One warning, three wordings
The US warning, section 5.3, links kidney injury to volume depletion: fluid going out faster than it comes in. It describes postmarketing reports of kidney injury, some requiring haemodialysis, in people on GLP-1 receptor agonists or Zepbound®, most of whom had dehydrating stomach reactions first [1]. Section 6.2 adds acute kidney failure and worsening of chronic kidney failure to the list of voluntary reports, which carry no frequency [1].
Canada frames the same chain and adds that some reports came from people without known kidney disease [3]. The EU information for tirzepatide, sold there as Mounjaro®, asks patients to take precautions against both fluid depletion and electrolyte disturbances, and to consider this especially in older people [4].
| Source and measure | Zepbound® | Placebo |
|---|---|---|
| US label, Studies 1 and 2: acute kidney injury [1] | 0.5% | 0.2% |
| Canadian monograph, SURMOUNT-1, -2, -3: acute kidney injury [3] | 0.5% | 0.2% |
| US label: severe stomach and bowel reactions, 5 / 10 / 15 mg [1] | 1.7% / 2.5% / 3.1% | 1% |
| US label, Table 1: vomiting, 5 / 10 / 15 mg [1] | 8% / 11% / 13% | 2% |
| US label, Table 1: diarrhoea, 5 / 10 / 15 mg [1] | 19% / 21% / 23% | 8% |
| US label: stopped because of stomach reactions, 5 / 10 / 15 mg [1] | 1.9% / 3.3% / 4.3% | 0.5% |
Why the start and each step-up matter
The label’s monitoring advice names two moments: starting Zepbound® and raising the dose [1]. That is when most nausea, vomiting and diarrhoea happened in the trials, before becoming less frequent [1], and the step-up schedule, with at least four weeks at each dose, exists partly to reduce them [1]. Severe stomach reactions were as common in the sleep apnea trials as in the weight trials [1].
A 2025 meta-analysis of six randomised trials in people with overweight or obesity but no diabetes, the main Zepbound® population, found vomiting about six times and serious stomach events about three times as likely as on placebo (risk ratios 5.94 and 3.07) [8]. Relative risks do not tell you how many people are affected, but they show why the label keeps attention on fluids in this group.
How fluid loss turns into kidney injury
- Backed by the product information: stomach reactions cause dehydration, and dehydration can worsen kidney function up to acute kidney failure [1][3][4]. The same chain shows in another row: low blood pressure occurred in 1.6% on Zepbound® and 0.1% on placebo, sometimes alongside stomach reactions and dehydration [1].
- Plausible but not measured: Zepbound® lowers calorie intake, most likely by acting on appetite [1]. Whether people also drink less while their appetite is low, adding to the deficit, was not measured in the documents we checked.
- General medical knowledge: MedlinePlus defines acute kidney failure as a loss of the kidneys’ ability to clear waste and balance fluids and electrolytes over less than two days, and lists reduced blood flow from very low blood pressure, including from dehydration, among its causes [9].
Living with reduced kidney function
The US label recommends no dose adjustment for kidney impairment: after a single dose, tirzepatide levels were the same in people with mild, moderate or severe impairment or end-stage disease as in people with normal kidneys, and trial data in people with overweight or obesity agreed [1]. What it repeats is the monitoring advice when fluid-losing reactions occur [1].
The other two regulators add limits. In Canada’s weight trials, 850 people on Zepbound® (30.3%) had mild and 59 (2.1%) moderate impairment, but no one had severe impairment, and Canada does not recommend Zepbound® in end-stage kidney disease because experience is very limited [3]. The EU calls for caution in severe impairment and end-stage disease for the same reason [4]. Canada’s patient information asks you to tell your healthcare professional about serious kidney problems before starting [3].
Canada raises one more point specific to its product. Zepbound® is sold there only as a multi-dose KwikPen, each dose of which contains 5.4 mg of benzyl alcohol as a preservative; people with kidney or liver impairment should be told about the possible risk of metabolic acidosis, acid build-up in the blood, if it accumulates over time [3]. In the US, the multi-dose vial and KwikPen contain the same amount per dose, while the single-dose pen and vial do not list it [1].
What kidney measurements in SURMOUNT showed
Two tests are used to follow kidney health: a blood test that estimates how well the kidneys filter (eGFR), and a urine albumin-to-creatinine ratio (UACR), because albumin leaks into urine when kidneys are damaged; the NIH treats a UACR above 30 mg/g as a possible sign of kidney disease [11]. A post hoc analysis of SURMOUNT-1 (2,539 people without diabetes) and SURMOUNT-2 (938 with type 2 diabetes) compared both measures after 72 weeks [5].
Compared with placebo, UACR fell by 8.4% in SURMOUNT-1 and 31.1% in SURMOUNT-2, with larger falls in people who started above 30 mg/g [5]. Estimated kidney function did not worsen; in SURMOUNT-1 a cystatin-C-based estimate was 3.2 units higher than on placebo, while SURMOUNT-2 showed no difference between groups [5]. Several authors were Lilly employees, the analysis was not planned when the trials began, and it measured markers rather than kidney failure or dialysis. None of the product documents lists kidney protection as a use of Zepbound® [1][3][4].
A separate post hoc analysis of adults aged 65 and over across SURMOUNT, the sleep apnea trials and SUMMIT found no clinically meaningful difference from placebo in renal adverse events [6]. Outside trials, an analysis of FDA spontaneous reports for tirzepatide placed dehydration among the signals more often tied to serious outcomes, though such data cannot prove cause [7].
Other reasons kidneys can struggle
MedlinePlus lists many causes of sudden kidney failure unrelated to Zepbound®: very low blood pressure from bleeding, burns, severe infection, surgery or dehydration; infections of the kidney itself; blood clots in kidney vessels; a blocked urinary tract; and medicines including non-steroidal anti-inflammatory painkillers (NSAIDs), certain antibiotics and blood pressure medicines, and contrast dye used for scans [9].
Dehydration itself has other sources too: fever, heavy sweating in hot weather or during exercise, and medicines or illnesses that make you pass more urine [10]. MedlinePlus notes that older adults may lose their sense of thirst, and that people with diabetes or kidney problems are more prone to dehydration [10]. If any of these apply alongside stomach side effects, they add up.
What the sources describe
- Drink fluids to lower the chance of dehydration; the Medication Guide and Canada’s patient information both ask for this [2][3].
- Fluid needs differ from person to person, so MedlinePlus suggests asking your provider how much you should drink each day [10].
- When you are unwell, take extra fluids; if keeping liquids down is hard, MedlinePlus suggests small sips of water or ice chips [10].
- Report nausea, vomiting or diarrhoea that does not settle to your provider promptly [2].
- MedlinePlus advises avoiding medicines that can injure the kidneys; ask your pharmacist before using an NSAID painkiller while you are losing fluids [9].
Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Eli Lilly and Company.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Confusion, fainting, no urine, a racing heartbeat or fast breathing | Get medical help right away | Emergency | MedlinePlus [10] |
| Dark yellow, strong-smelling urine, extreme thirst, or feeling dizzy or light-headed | Stop Zepbound® and seek immediate medical help | Emergency | Canadian patient information [3] |
| Nausea, vomiting or diarrhoea that keeps going | Your healthcare provider, straight away | Today | Medication Guide [2] |
| Passing much less urine than usual, or urine that stops | Contact your provider | Today | MedlinePlus [9] |
| Known kidney disease, or kidney or liver problems while using a multi-dose KwikPen | Your prescriber, before starting or stepping up | At your next appointment | US label [1]; Canadian monograph [3] |
| Regular use of NSAID painkillers, diuretics or blood pressure medicines | Your prescriber or pharmacist | At your next appointment | MedlinePlus [9] |
