Budesonide Side Effects in Dogs and Cats

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

Budesonide is a prescription glucocorticoid (steroid) given to dogs and cats for inflammatory conditions, most often chronic inflammatory bowel disease and other chronic enteropathies [1][2]. It is a locally acting steroid with high first-pass metabolism through the liver, which means less of the active drug reaches the general circulation compared with prednisone or prednisolone [1][3]. That design lowers the risk of systemic steroid side effects, but it does not eliminate them. Dogs and cats on budesonide can still develop increased thirst and urination, increased appetite, weight gain, panting, vomiting, diarrhea, adrenal gland suppression, liver enzyme changes, and unmasking of diabetes. The most important monitoring step is a baseline blood panel, urinalysis, and then scheduled rechecks, because many of these effects are detected on lab work before an owner notices anything at home [4].

This article is educational and is not a substitute for veterinary diagnosis or treatment.

At a Glance

What Budesonide Is and What It Treats

Budesonide belongs to the glucocorticoid class of medications. Glucocorticoids reduce inflammation by changing how immune cells behave, and they are a mainstay of treatment for inflammatory and immune-mediated disease in small animals. Budesonide is different from older steroids such as prednisone and prednisolone because it is designed to act mostly where it is applied or absorbed in the gut, then to be broken down quickly by the liver before it can circulate widely through the body [1][3].

That property is why veterinarians reach for budesonide in dogs with chronic enteropathy, also called idiopathic inflammatory bowel disease. The goal is to calm inflammation in the intestinal lining while producing fewer of the whole-body steroid effects that owners dislike, such as heavy drinking, heavy urination, and constant hunger [1][2].

Budesonide is also used in other forms and settings. It has been studied as an inhaled medication in dogs with airway disease, and it has been studied as a topical preparation for canine skin [5][6]. The side effect profile differs somewhat by route. An inhaled or topical product delivers drug mostly to the target tissue, while an oral product is swallowed and absorbed through the gut. Most owner questions about budesonide side effects concern the oral form used for gastrointestinal disease, so that is the focus here.

How Budesonide Works and Why It Has Fewer Systemic Effects

After a dog or cat swallows budesonide, the drug is absorbed from the gastrointestinal tract. From there it passes through the liver before reaching the rest of the body. The liver metabolizes budesonide extensively, converting much of it into less active compounds. This is called first-pass metabolism, and it is the reason systemic exposure is lower than with prednisolone [1][3].

A pharmacokinetic study in dogs with inflammatory bowel disease measured plasma and urine concentrations of budesonide and its metabolite after oral dosing. The drug was rapidly absorbed, and the ratio of unchanged budesonide to its metabolite in urine was very low, which supports the idea that most of the drug is converted before it can act systemically [1]. In practical terms, the drug does its anti-inflammatory work in the gut wall and then gets cleared.

Lower systemic exposure does not mean no systemic exposure. Some drug always escapes first-pass metabolism, and the amount that escapes can vary between animals, between formulations, and with liver function. A dog with liver disease may clear budesonide more slowly, which can raise blood levels and increase the risk of side effects. This is one reason baseline blood work matters before starting treatment and why rechecks matter afterward.

What Budesonide Does Not Cover

Budesonide is not an antibiotic, an antiparasitic, or a pain reliever. It does not treat infections, and in fact its immune-suppressing effects can make some infections worse or allow dormant infections to flare [7]. It is not a substitute for a proper diagnosis. A dog with chronic diarrhea may have inflammatory bowel disease, but it may also have parasites, a food-responsive enteropathy, a bacterial imbalance, or cancer. Steroids can mask or worsen some of these conditions, so a veterinarian needs to sort out the cause before or alongside starting budesonide.

Budesonide also does not replace dietary management. Many dogs with chronic enteropathy improve with a change in diet, and some improve with diet alone. Budesonide is typically one part of a plan that may include diet, parasite control, and other medications.

How Budesonide Is Given

Budesonide is given by mouth, usually once daily. In the controlled trial that compared budesonide with prednisone for canine inflammatory bowel disease, dosing was weight-based and ranged from 1 mg once daily in small dogs up to 5 mg once daily in dogs over 30 kg [2]. A separate pharmacokinetic study used a body-surface-area based dose of 3 mg/m² once daily [1]. These are study doses, not a dosing chart for home use. The exact dose for any individual pet is set by the prescribing veterinarian based on weight, condition, formulation, and other health factors.

Practical points that reduce problems:

• Give the medication at the same time each day unless the veterinarian says otherwise.
• Follow the label or the veterinarian's instructions about giving it with or without food.
• Do not split, crush, or compound the medication unless the veterinarian or pharmacist confirms it is safe for that specific product.
• Do not stop suddenly after long-term use. Steroids suppress the adrenal glands, and abrupt withdrawal can cause a crisis. Tapering is usually required, and the taper plan comes from the veterinarian.
• Keep a simple log of appetite, water intake, urination, vomiting, diarrhea, and energy. This log is genuinely useful at recheck visits.

Common Budesonide Side Effects

Even with reduced systemic exposure, a meaningful number of dogs on budesonide show steroid-type side effects. In the randomized trial comparing budesonide and prednisone for canine IBD, the frequency of owner-reported adverse effects was similar between the two groups [2]. That finding surprises many owners, because budesonide is often described as the gentler steroid. The honest summary is that budesonide tends to produce fewer or milder systemic effects in many patients, but in a head-to-head trial the overall rate of reported side effects was not clearly lower than prednisone [2]. A later evidence review of the same comparison noted that remission rates and adverse effect frequency were similar between the two drugs, while pointing out that the evidence base is limited and more studies are needed [8].

Increased Thirst and Urination (Polyuria and Polydipsia)

Increased drinking and urination are the most recognizable steroid effects. Steroids change how the kidney handles water and can increase urine output, which drives the pet to drink more. Owners may notice a water bowl that empties faster, more trips outside, or accidents in a previously reliable dog. In cats, a litter box that needs more frequent cleaning is the common clue.

These signs are usually manageable but should be reported. Heavy urination can be a sign of diabetes, which steroids can unmask, so new or worsening thirst and urination deserve a veterinary call rather than watchful waiting.

Increased Appetite (Polyphagia) and Weight Gain

Steroids increase appetite. A dog that previously ate politely may start begging, scavenging, and eating faster. Weight gain follows from the extra calories plus steroid-related changes in body composition and fluid retention. Weight gain is one of the most common owner complaints during steroid therapy.

Managing this is practical. Measure food rather than free-feeding, use a measured scoop, and resist extra treats. If the pet is constantly hungry, ask the veterinarian whether the dose can be adjusted or whether a higher-fiber diet would help. Do not change the dose on your own.

Panting and Restlessness

Dogs on steroids often pant more, especially at rest or at night. Some become restless or pace. This can be distressing for owners, but it is usually a direct drug effect rather than pain or anxiety. It tends to improve as the dose is reduced. Report severe or sudden panting, especially if it comes with weakness, collapse, or a distended abdomen, because those can signal a more serious problem.

Gastrointestinal Upset

Vomiting, diarrhea, and reduced appetite can occur. This is a particular challenge in pets being treated for gastrointestinal disease, because it can be hard to tell whether a symptom is the disease or the drug. In the budesonide versus prednisone trial, adverse effects were reported in both groups at similar rates [2]. If vomiting or diarrhea worsens after starting budesonide, contact the veterinarian. Do not assume it is just the medication and wait.

Muscle Weakness and Changes in Appearance

Long-term steroid use can cause muscle wasting, a pot-bellied appearance, and thinning of the skin. These changes are more associated with higher systemic steroid exposure, but they can appear with budesonide over time, particularly at higher doses or in animals with reduced liver clearance.

Behavioral Changes

Some pets become irritable, anxious, or unusually vocal on steroids. Cats may seem more agitated or hide more. These changes are usually dose-related and improve with tapering. Report marked behavior changes so the veterinarian can weigh the benefits of the drug against the impact on the pet's quality of life.

Serious Budesonide Side Effects

Serious effects are less common than the nuisance effects above, but they are the reason monitoring exists. They include adrenal suppression, liver problems, unmasking of diabetes, and immune suppression that allows infections to take hold.

Adrenal Suppression

The adrenal glands produce cortisol, the body's natural steroid. When a pet receives an external steroid, the adrenal glands can reduce their own production. This is called adrenal suppression or suppression of the hypothalamic-pituitary-adrenal (HPA) axis.

Budesonide can suppress the HPA axis in dogs. In a 30-day clinical trial in dogs with inflammatory bowel disease, oral budesonide at 3 mg/m² once daily caused significant suppression of the HPA axis, measured by basal cortisol, ACTH-stimulated cortisol, and endogenous ACTH [4]. That is a direct and important finding. It means budesonide is not adrenal-sparing in every patient, and it means a dog on budesonide may not respond normally to stress, illness, surgery, or anesthesia.

How budesonide compares with other steroids on this measure is more nuanced. In a study of healthy Beagle dogs, inhaled budesonide at 200 µg twice daily for four weeks did not suppress cortisol production, while oral prednisolone at 1 mg/kg once daily strongly suppressed it, and inhaled fluticasone also suppressed ACTH-stimulated cortisol [5]. That study used the inhaled route, so it does not directly answer questions about oral budesonide for gut disease. Taken together, the evidence shows that route, dose, and formulation all matter, and that oral budesonide can suppress the adrenal axis even though it is designed to limit systemic exposure [5][4].

Practically, adrenal suppression means:

• Do not stop budesonide abruptly after long-term use. The veterinarian will design a taper.
• Tell any veterinarian treating your pet for a new problem that the pet is on budesonide.
• If the pet becomes severely ill, vomits repeatedly, collapses, or seems weak and unresponsive, seek emergency care and mention the steroid.
• Before surgery or major procedures, the veterinarian may need to adjust or supplement steroid coverage.

Liver Effects (Hepatopathy)

The liver is central to how budesonide is handled, and it is also a site where steroid effects can show up. Steroids commonly raise serum alkaline phosphatase (SAP) activity in dogs. In the 30-day budesonide trial in dogs with IBD, there was no significant difference in SAP activity before and after treatment [4]. That is reassuring but not a guarantee, because the study was small and short.

The bigger concern is pre-existing liver disease. Because budesonide depends on the liver for clearance, a dog with compromised liver function may clear the drug more slowly, leading to higher blood levels and more systemic effects. Dogs with known liver disease need careful baseline assessment and closer monitoring when starting budesonide. In general toxicity studies of steroids in dogs, treatment-related changes have been observed in the liver along with the adrenals, thymus, lymph nodes, and spleen, which is the expected pattern for a glucocorticoid [9]. Any new jaundice, profound lethargy, vomiting, or abdominal swelling on budesonide warrants prompt veterinary attention.

Unmasking of Diabetes Mellitus

Steroids raise blood glucose. They increase glucose production by the liver and reduce glucose uptake by tissues. In a pet with borderline diabetes, or with an underlying tendency toward it, budesonide can push blood sugar over the threshold and bring out obvious diabetes. The classic signs are the same as the steroid thirst and urination signs but more severe: heavy drinking, heavy urination, weight loss despite a good or increased appetite, and in dogs, cataracts.

Cats deserve special mention. Cats tolerate budesonide well in general, but they are prone to hyperglycemia on steroids, and stress alone can raise a cat's blood sugar. Monitoring blood glucose and urine glucose in cats on budesonide is a reasonable precaution, especially in cats that are older, overweight, or already have borderline glucose values. Any cat that starts drinking and urinating heavily on budesonide should be evaluated for diabetes.

Immune Suppression and Infection Risk

Glucocorticoids suppress the immune system. That is part of how they control inflammatory disease, but it also means a pet on budesonide may be less able to fight infections. The most dramatic illustration in the veterinary literature is a case report of a young Pomeranian on long-term budesonide for presumed inflammatory bowel disease who developed disseminated Strongyloides stercoralis infection involving the lungs, small intestine, and kidney [7]. The dog was euthanized after respiratory collapse. This is a single case, and it does not mean every pet on budesonide will develop a disseminated parasite infection. It does mean that immune suppression from budesonide is real, that it can be serious, and that pets on steroids with chronic diarrhea should be screened for parasites and monitored for new or worsening respiratory or gastrointestinal signs.

Owners should watch for:

• New or worsening cough, difficulty breathing, or rapid breathing
• Persistent or bloody diarrhea
• Fever, lethargy, or poor appetite
• Non-healing wounds or skin infections
• Any sign of illness that seems out of proportion to the pet's condition

Budesonide Side Effects in Cats

Cats generally handle budesonide well, and it is used in cats for chronic gastrointestinal and inflammatory conditions. The main practical concern in cats is blood sugar. Steroids can cause hyperglycemia in cats, and cats can be tipped into clinical diabetes by steroid therapy. Cats also hide illness well, so subtle changes in water intake, litter box use, appetite, and weight are the clues owners should track.

Cats on budesonide should have baseline blood work and urinalysis, and rechecks that include glucose monitoring. If a cat develops increased thirst, increased urination, weight loss despite a good appetite, or new lethargy, the veterinarian should assess for diabetes. Cats can also develop the same general steroid effects as dogs, including increased appetite, weight gain, and behavioral changes, though these are often less dramatic.

Which Pets Should Not Receive Budesonide

Budesonide is not appropriate for every pet. A veterinarian will weigh the risks and benefits, but situations that raise concern include:

• Known or suspected liver disease, because budesonide clearance depends on the liver
• Diabetes mellitus or borderline hyperglycemia, because steroids raise blood glucose
• Active systemic infections, including fungal infections, because steroids suppress the immune response
• Pets with a history of adverse reactions to glucocorticoids
• Pets on other immune-suppressing medications, because the combined effect increases infection risk
• Pregnant or breeding animals, unless the veterinarian specifically recommends it
• Pets with certain eye conditions, such as corneal ulcers, because steroids can worsen some ocular diseases

This list is not exhaustive. Always give the veterinarian the full medication and supplement history before starting budesonide.

Drug Interactions to Know About

Budesonide is metabolized by liver enzymes, so drugs that affect those enzymes can change budesonide levels. This is a genuine interaction concern, and the veterinarian should review every medication the pet receives. Categories to discuss include:

• Other corticosteroids, such as prednisone or prednisolone, because the effects add up
• Certain antifungal medications, which can slow budesonide breakdown and raise blood levels
• Certain antibiotics, including some macrolides, which can have similar effects
• Nonsteroidal anti-inflammatory drugs (NSAIDs), because steroids plus NSAIDs increase the risk of gastrointestinal ulceration
• Diuretics such as furosemide, because steroids can worsen potassium loss
• Antidiabetic medications, because steroids raise blood glucose and can reduce their effectiveness
• Vaccines, because immune suppression can reduce vaccine response

Do not stop or start any medication, supplement, or herbal product without telling the veterinarian. Some over-the-counter products affect liver enzymes.

Monitoring: What to Expect and When

Monitoring is the single most important thing an owner can do to catch budesonide side effects early. The schedule below reflects standard small animal practice for a pet starting a glucocorticoid for a chronic inflammatory condition. The exact timing is set by the veterinarian based on the pet's condition, dose, and other health problems.

Additional monitoring may include an ACTH stimulation test to assess adrenal function, especially before anesthesia or if the pet becomes ill, and specific testing if an infection is suspected. The 30-day study in dogs with IBD used basal cortisol, ACTH-stimulated cortisol, endogenous ACTH, SAP activity, and urine specific gravity to track budesonide effects [4]. That gives a sense of the tools available, though not every pet needs every test at every visit.

Owners can support monitoring by keeping a simple daily record:

• How much water the pet drinks (measure the bowl if possible)
• How often the pet urinates, and whether there are accidents
• Appetite and food intake
• Vomiting or diarrhea episodes
• Energy level and behavior
• Weight, if a home scale is available

Bring this log to every recheck. Patterns that are obvious over weeks can be invisible day to day.

How Budesonide Compares With Other Steroids

The main alternative to budesonide for inflammatory bowel disease in dogs is prednisone or prednisolone. The key comparison points:

• Efficacy: In a randomized controlled trial of 40 dogs with newly diagnosed idiopathic IBD, remission rates were 78% in the budesonide group and 69% in the prednisone group, a difference that was not statistically significant [2]. A later evidence review concluded that no significant difference in remission rates was observed between the two drugs [8].
• Side effects: In the same trial, the frequency of owner-reported adverse effects was similar between budesonide and prednisone [2]. The evidence review reached the same conclusion [8].
• Adrenal effects: In healthy dogs, oral prednisolone strongly suppressed cortisol production, while inhaled budesonide did not [5]. Oral budesonide, however, has been shown to suppress the HPA axis in dogs with IBD [4]. Route and formulation matter.
• Liver handling: Budesonide undergoes extensive first-pass metabolism, which is its main design advantage [1][3]. Prednisolone is more systemically available.

The practical takeaway is that budesonide is a reasonable option for dogs with chronic enteropathy, and it may produce fewer systemic effects in some patients, but it is not a free pass. It can cause the same categories of side effects, and it requires the same monitoring discipline.

Topical budesonide formulations have also been studied in dogs. A skin penetration study found that the formulation strongly affects how much budesonide penetrates and is retained in canine skin, with one formulation delivering substantially more drug to the skin than others [6]. That matters for topical therapy, where the goal is to keep drug at the site of action and limit systemic absorption, but it also means different topical products are not interchangeable.

What to Do About Side Effects at Home

Most common budesonide side effects are managed with dose adjustment, timing changes, and supportive care. The veterinarian may lower the dose, change how it is given, or add another medication. Never adjust the dose yourself.

Practical steps owners can take:

• For increased thirst and urination: Keep fresh water available. Do not restrict water unless the veterinarian specifically instructs it, because restricting water in a pet on steroids can be dangerous. Provide more frequent bathroom breaks.
• For increased appetite and weight gain: Measure food. Use a fixed scoop. Limit treats and table food. Ask about a higher-fiber or weight-management diet.
• For panting and restlessness: Keep the pet cool and calm. Report severe or sudden panting.
• For vomiting or diarrhea: Contact the veterinarian. Do not assume it is the drug. A pet being treated for gut disease that worsens needs evaluation.
• For behavioral changes: Note what changed and when. Report it at the next visit or sooner if it is severe.
• For any sign of diabetes: Increased thirst, increased urination, weight loss despite good appetite, or new cataracts warrant prompt testing.
• For any sign of infection: Cough, breathing difficulty, fever, lethargy, or non-healing wounds need veterinary attention.

Never stop budesonide abruptly after long-term use. The adrenal glands may not recover quickly, and stopping suddenly can cause a life-threatening crisis. The veterinarian will provide a taper plan.

Limitations and When to Contact a Veterinarian

This article is educational and is not a substitute for veterinary diagnosis or treatment. Every pet is different, and the right dose, monitoring plan, and duration of treatment depend on the individual animal, the underlying disease, and other health conditions. Your veterinarian is the only person who can give advice for your pet.

Contact a veterinarian promptly if any of the following occur:

• Heavy drinking or urination that is new or worsening
• Vomiting that does not stop, or vomiting with blood
• Diarrhea that is severe, bloody, or accompanied by lethargy
• Weight loss despite a good appetite
• New cough, difficulty breathing, or rapid breathing
• Collapse, severe weakness, or unresponsiveness
• Yellow gums, eyes, or skin
• A distended or painful abdomen
• Seizures or sudden blindness
• Any sign that seems severe or is getting worse quickly

Seek emergency care immediately for collapse, difficulty breathing, seizures, or a pet that cannot stand. Tell the emergency team that the pet is on budesonide and when the last dose was given.

Frequently Asked Questions

Are budesonide side effects in dogs common?

Yes, steroid-type side effects are common in dogs on budesonide. In a randomized trial comparing budesonide with prednisone for canine inflammatory bowel disease, the frequency of owner-reported adverse effects was similar between the two groups [2]. Increased thirst, increased urination, increased appetite, and weight gain are the most frequently reported.

Is budesonide safer than prednisone for dogs?

Budesonide is designed to have lower systemic exposure than prednisone because of high first-pass liver metabolism [1][3]. In practice, some dogs tolerate it better, but a controlled trial found similar remission rates and similar rates of owner-reported adverse effects between budesonide and prednisone [2]. It is not automatically safer for every dog.

Can budesonide cause liver problems in dogs?

Budesonide is cleared by the liver, so dogs with pre-existing liver disease may clear it more slowly and develop higher blood levels. A 30-day study in dogs with inflammatory bowel disease found no significant change in serum alkaline phosphatase activity, but the study was small and short [4]. Liver monitoring is part of routine rechecks.

Does budesonide suppress the adrenal glands in dogs?

Yes, it can. A 30-day clinical trial in dogs with inflammatory bowel disease found significant suppression of the hypothalamic-pituitary-adrenal axis on oral budesonide at 3 mg/m² once daily [4]. This is why budesonide should not be stopped abruptly after long-term use and why the adrenal axis may need testing before surgery or during serious illness.

Can budesonide cause diabetes in dogs or cats?

Steroids raise blood glucose and can unmask diabetes in a pet that was already borderline. Cats are particularly prone to steroid-related hyperglycemia. Monitor for increased thirst, increased urination, and weight loss despite a good appetite, and have blood glucose checked at rechecks.

Do cats get the same budesonide side effects as dogs?

Cats generally tolerate budesonide well, but they can develop increased appetite, weight gain, and behavioral changes. The main concern in cats is hyperglycemia and unmasking of diabetes. Cats on budesonide should have regular blood work and urinalysis, including glucose monitoring.

How often should a pet on budesonide have blood work?

A reasonable schedule is a baseline CBC, biochemistry panel, and urinalysis before starting, a recheck at 2 to 4 weeks, and then monitoring every 3 to 6 months while the pet remains on the medication. The veterinarian may adjust this based on the pet's condition and dose.

Can I stop budesonide suddenly if my pet seems fine?

No. Long-term steroid use can suppress the adrenal glands, and stopping suddenly can cause a life-threatening crisis [4]. Always taper under veterinary direction, even if your pet looks completely normal.

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Sources

1. Plasma concentrations and therapeutic effects of budesonide in dogs with inflammatory bowel disease.
2. Randomized, controlled trial of budesonide and prednisone for the treatment of idiopathic inflammatory bowel disease in dogs.
3. Pharmacokinetic studies of a potent glucocorticoid (budesonide) in dogs by high-performance liquid chromatography.
4. Clinical effects of short-term oral budesonide on the hypothalamic-pituitary-adrenal axis in dogs with inflammatory bowel disease.
5. Endocrine effects of inhaled budesonide compared with inhaled fluticasone propionate and oral prednisolone in healthy Beagle dogs.
6. The effects of formulation on the penetration and retention of budesonide in canine skin in vitro.
7. Disseminated Strongyloides stercoralis infection in a dog following long-term treatment with budesonide.
8. In dogs with chronic enteropathy (idiopathic inflammatory bowel disease) is budesonide more effective than prednisolone or prednisone in resolving clinical signs?
9. 28-day oral toxicity study with soft corticosteroid BNP-166 in rats and dogs, followed by a 14-day recovery period.