Constipation

Constipation is one of the more underappreciated problems in cats with chronic kidney disease, and it tends to be underrecognized until it becomes serious. Many owners and even some vets do not connect reduced litter box output to kidney disease, but the two are closely linked. Understanding why constipation happens in CKD cats, catching it early, and managing it consistently can make a significant difference to how your cat feels day to day and can prevent acute episodes that require emergency care.

The connection between kidney disease and constipation is primarily driven by dehydration. CKD cats produce large volumes of dilute urine because their damaged kidneys can no longer concentrate it effectively. This means the body is constantly losing more fluid than it ideally takes in. The intestines respond to this by extracting as much water as possible from stool as it passes through, leaving it dry, hard, and difficult to pass.

At the same time, the uremic toxins that build up in CKD have been shown to affect gut motility directly. Research suggests that indoxyl sulfate, one of the major uremic toxins, may slow colonic movement, meaning stool spends longer in the large intestine and becomes even drier in the process.

Several other factors common in CKD cats compound the problem. Low potassium levels, which are frequent in CKD, can impair muscle function throughout the body including in the gut. High calcium levels, when present, can also contribute. Some medications prescribed for CKD cats, including certain phosphorus binders and sucralfate, have constipation as a known side effect. Pain medications used in older cats, particularly opioid-based ones, can also slow gut transit.

Older age and reduced activity, which often accompany CKD, add further risk. A cat that is not moving around much is also not stimulating gut motility in the way a more active cat would.

More common than many vets and owners realize. A 2022 survey-based study by Jones, Quimby and colleagues found that 42% of CKD cats defecated less than once per day, compared to only 15% of apparently healthy cats. The same study noted that constipation in CKD cats is likely under-recognized, with subclinical cases going unnoticed until they become acute.

A 2025 follow-up study by George, Quimby and colleagues used smart litter box monitors over 30 days to objectively measure defecation frequency, confirming that CKD cats defecated less frequently than healthy cats and had more days with no defecation events at all. The authors noted that constipation can destabilize a CKD cat significantly, sometimes requiring emergency treatment and hospitalization.

The practical implication is that monitoring your cat’s litter box output is not optional. It is one of the most valuable things you can do at home.

The most obvious signs are the ones you would expect: reduced frequency of stools, straining in the litter tray, or stools that are noticeably dry and hard when you see them. But constipation in cats can present in ways that are much less obvious.

Changes in litter box frequency. Knowing your cat’s normal is essential. Most healthy cats defecate at least once a day. A CKD cat producing a stool every two or three days, or less, is showing a pattern worth monitoring closely and discussing with your vet. Consider cleaning the litter tray daily and keeping a simple note of what you find. It takes 30 seconds and can catch a problem before it becomes a crisis.

Straining or prolonged time in the tray. A cat that spends an unusually long time in the litter box, adopts an exaggerated posture, or makes multiple unsuccessful visits may be constipated. This symptom can also indicate a urinary problem, so if you are unsure whether your cat is passing urine normally, contact your vet promptly. Inability to urinate is a genuine emergency.

Hard, dry, or very small stools. If you do see stools, check their consistency. Normal cat stool should be firm but not rock-hard, and not crumbling or chalky. Stools that are very small, very dry, or resemble pellets are a sign the intestine is removing too much water.

Reduced appetite and lethargy. A constipated cat often feels generally unwell. Backed-up stool is uncomfortable and the pressure it creates can cause nausea and appetite loss that looks similar to uremia-driven symptoms. If your cat’s appetite suddenly worsens without another obvious explanation, constipation is worth considering.

Vomiting around litter tray time. Some cats vomit before, during, or immediately after attempting to defecate when severely constipated. This happens because distension of the colon triggers the vomiting reflex via stretch receptors. If your cat’s vomiting episodes consistently occur around litter box visits, constipation may be the cause even if you have not noticed reduced stool output.

Urinating outside the litter tray. A full colon puts physical pressure on the bladder, reducing how much it can hold and sometimes triggering inappropriate urination. Many owners assume inappropriate urination points to a urinary tract infection or behavioral problem and never investigate the bowel. If your cat is urinating in unusual places and a UTI has been ruled out, ask your vet about the possibility of constipation.

What looks like diarrhea. If your cat has severe constipation with impacted stool, sometimes only liquid or semi-liquid material can squeeze past the blockage. This is called overflow incontinence and looks exactly like diarrhea. Treating it as diarrhea makes the real problem worse. If you see what appears to be diarrhea in a cat who has recently had reduced stool output, or in a cat who seems uncomfortable and is straining, raise this with your vet before giving any anti-diarrhea treatment.

Fast breathing or elevated heart rate. In cases of very severe constipation, toxin buildup and pain can cause rapid breathing or an elevated heart rate. These are signs of significant distress and require same-day veterinary attention.

Contact your vet promptly if your cat:

• Has not produced a stool in more than two days
• Is straining without producing anything
• Appears to be in pain or distress in or around the litter tray
• Is showing the unexpected symptoms described above, particularly if more than one is present
• Has been vomiting alongside reduced litter tray output
• Has what appears to be diarrhea but also seems uncomfortable or has recently had reduced stool frequency

A cat with impacted stool needs veterinary treatment. Do not attempt to manage severe acute constipation at home with laxatives alone: a blocked colon needs to be cleared before maintenance treatments will work properly.

When constipation has progressed to the point where the cat cannot pass stool at all, or the stool is impacted, veterinary intervention is needed. The treatments used depend on how severe the problem is.

Fluid therapy. Because dehydration is such a major driver of constipation in CKD cats, intravenous or subcutaneous fluids are often the first step when a cat presents with significant constipation. Rehydrating the cat softens the stool and restores gut motility to some degree. This alone can sometimes resolve mild to moderate constipation, particularly in cats who have become acutely dehydrated.

Enemas. Your vet can administer an enema to help soften and move impacted stool. This is usually done at the clinic. If your cat has chronic severe constipation, some vets will teach owners how to give enemas at home, but this is a clinical decision for your vet to make.

One critical safety note: enemas containing sodium phosphate, sold under brand names such as Fleet in the USA, must never be used in cats. They can cause life-threatening electrolyte imbalances including severe phosphorus and calcium abnormalities, and these risks are heightened in cats with CKD. Only use enemas that your vet has specifically approved for your cat.

Manual evacuation. If an enema is not sufficient, your vet may need to manually remove impacted stool under sedation or anesthesia. This is uncomfortable and requires recovery time afterward, which is why preventing constipation from reaching this stage is so important.

Once an acute episode has been resolved, the focus shifts to preventing it from recurring. The treatments described in the next section are the tools for doing that.

The goal of chronic management is to prevent constipation from developing or recurring, using the least intervention necessary. Most cats can be managed well with a combination of good hydration and one or two additional treatments. A small number of cats with severe chronic constipation or megacolon need prescription medications on an ongoing basis.

Hydration first

Hydration is the foundation of constipation management in CKD cats. No laxative or dietary intervention will work as well as it should if your cat is chronically dehydrated. The intestines are constantly extracting water from stool when the body is short of fluid, and this overrides everything else.

Make sure your cat has access to plenty of water in appealing forms: multiple water sources, wet food as the main diet, and water added to food where it is accepted. Cats already receiving subcutaneous fluids regularly will often find constipation improves along with their hydration status. If your cat is not yet on subcutaneous fluids but constipation is a persistent problem alongside moderate or advanced CKD, raising the question of fluid therapy with your vet is worthwhile.

For more detail on supporting hydration, see Maintaining Hydration in Cats with Kidney Disease.

Diet and fibre

Feeding wet food rather than dry is one of the most important dietary changes for a constipated CKD cat. The water content of wet food contributes meaningfully to overall hydration and stool consistency. Dry food contributes very little moisture and leaves the intestine with more work to do.

Adding modest amounts of dietary fibre can help bulk up and soften stools, making them easier to pass. Sources that work for some cats include canned plain pumpkin, cooked peas, and psyllium husk in small amounts. Fibre works by retaining water in the stool, so it is important that the cat is adequately hydrated when fibre is added: fibre given to a dehydrated cat can make constipation worse. Start with a very small amount, around half a teaspoon of pumpkin or a pinch of psyllium, and increase gradually based on response.

Fibre should not be used if the cat already has impacted stool. It is a preventative tool, not a treatment for acute blockage.

Polyethylene glycol 3350 (PEG 3350 / MiraLax)

PEG 3350, sold over the counter in the USA as MiraLax and in Canada as RestoraLax or Lax-A-Day, is an osmotic laxative that retains water within the colon rather than drawing it from the rest of the body. This is an important distinction from some other laxatives, making it gentler on overall hydration. It is well tolerated in cats, tasteless and odourless, and can be mixed into food. It is currently the most commonly recommended laxative for constipation management in CKD cats.

Dosing is highly individual and needs to be titrated to the response you see. A commonly used starting dose is one-eighth of a teaspoon per day. If this produces no improvement after two to three days, the dose can be increased incrementally. The goal is consistent, normally formed stools, not diarrhea. If stools become too loose, the dose should be reduced.

The MiraLax packaging carries a warning about use in patients with kidney disease, which causes understandable concern. This warning relates to the high-dose bowel-cleansing use in humans before procedures, which can cause electrolyte imbalances. At the low doses used for routine constipation management in cats, PEG 3350 does not have this effect. That said, always discuss any new medication with your vet before using it, and ask your vet to monitor your cat’s electrolytes periodically if PEG 3350 is used long term.

Choose a product that contains only PEG 3350 without added electrolytes, as the versions with electrolytes are designed for bowel cleansing and are not needed for constipation management.

Lactulose

Lactulose is another osmotic laxative, available as a syrup. Unlike PEG 3350, lactulose draws water into the colon from the rest of the body, which means it can contribute to dehydration if used in excess or without adequate fluid intake. It requires a prescription in the USA.

Lactulose has a secondary benefit that is potentially relevant to CKD cats: some studies in human CKD patients have found that lactulose may help reduce BUN and creatinine levels by promoting excretion of nitrogen compounds through the stool rather than the urine. Whether this effect is clinically meaningful in cats has not been well established, but it is a reason some vets prefer lactulose over PEG 3350 for CKD cats specifically.

On the downside, lactulose is a sugar syrup and is sticky and difficult to give. Some cats find the taste aversive. It should not be used in diabetic cats. It may also cause hypercalcemia with prolonged use in some cats.

Dosing is similarly individual and needs to be titrated. Your vet will guide the starting dose based on your cat’s size and the severity of constipation.

Slippery elm bark

This herbal supplement coats and soothes the digestive tract and has both mild laxative and anti-inflammatory properties. Some owners find it helpful as part of a constipation management plan, particularly in conjunction with dietary changes. It is generally considered safe but can affect the absorption of other medications if given at the same time, so space it away from medications and supplements by at least an hour. Inform your vet before using it.

Cisapride

Cisapride is a prescription prokinetic medication that stimulates muscle contractions in the colon, helping it move stool forward more effectively. It is most useful when constipation is driven primarily by reduced gut motility rather than just dry stool, and is often used alongside laxatives like PEG 3350 rather than instead of them.

Because cisapride was withdrawn from the human market in 2000 due to cardiac side effects in people, it is only available through compounding pharmacies in the USA. It appears to be safe for use in cats at the doses used in veterinary medicine, with the cardiac risks seen in humans linked to a specific gene channel that is much less relevant in cats. Nonetheless, it should be used cautiously in cats with known heart conditions, and it has interactions with several other medications including cimetidine and ondansetron. Your vet will assess whether it is appropriate for your cat and whether any medications your cat takes create a concern.

A typical dose is 2.5 to 5 mg per cat given two to three times daily, though dosing is adjusted to the individual.

What to avoid

Mineral oil. Do not give mineral oil orally. Because it has no smell or taste, cats can easily inhale it while swallowing, which can cause aspiration pneumonia. It should only ever be used rectally and only under veterinary direction.

Hairball remedies as a laxative. Products like Laxatone or Petromalt are designed to help pass hairballs and have limited effectiveness for the ongoing constipation seen in CKD cats. Long-term use may also reduce absorption of fat-soluble vitamins. They are not appropriate as a primary constipation treatment.

Enemas containing sodium phosphate. As noted above, these are dangerous for cats and must not be used.

Keeping track

Given how commonly constipation in CKD cats is under-recognized, building a simple monitoring habit is worthwhile. Clean the litter tray daily if possible and note whether a stool was present. If your cat goes two days without producing anything, contact your vet rather than waiting to see if it resolves. A minor constipation problem that is caught early is far easier to manage than one that has progressed to impaction.

• Jones SE, Quimby JM, Summers SC, Adams SM, Caney SMA and Rudinsky AJ (2022). Survey of defecation habits in apparently healthy and chronic kidney disease cats. Journal of Feline Medicine and Surgery 24(2), pp131-141.
• George ZM, Quimby JM, Jones S, Brusach KB and Rudinsky AJ (2025). Quantification of defecation frequency in cats with and without chronic kidney disease. Journal of Feline Medicine and Surgery 27. DOI: 10.1177/1098612X251348011.
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• Collier A (2025). Constipation, obstipation and megacolon in small animals. MSD Veterinary Manual.
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• 2022 ISFM consensus guidelines on management of the inappetent hospitalised cat. Taylor S et al. Journal of Feline Medicine and Surgery 24, pp614-640.