Prednisone can cause side effects in dogs ranging from mild nuisances like excessive thirst to serious complications like stomach ulcers, diabetes, and life-threatening adrenal crisis if the drug is stopped too abruptly. Most dogs on a short, low-dose course will only experience the milder end of this spectrum, but longer treatment at higher doses significantly raises the stakes. Understanding which effects are harmless (if annoying) and which ones demand immediate attention can help you advocate for your dog during treatment.
The Side Effects Nearly Every Dog Gets
Increased thirst is the single most common side effect, reported in about 39% of dogs in a large UK veterinary study. Increased urination follows close behind at 28%, and ravenous appetite affects roughly 14%. These three effects are so predictable that veterinarians sometimes call them the “PU/PD/PP” triad. They typically appear within about 12 days of starting oral prednisone, though injectable steroids can trigger them even sooner, around 8 days.
These effects aren’t dangerous on their own, but they can seriously disrupt daily life. Your dog may need to go outside far more often, have accidents indoors, drain the water bowl repeatedly, or beg relentlessly for food. Panting and restlessness are also common. All of these tend to resolve once the dose is tapered down or the medication is discontinued.
Digestive Problems and Stomach Ulcers
Vomiting occurs in about 16% of dogs on prednisone, and diarrhea in roughly 15%. In a controlled trial where healthy dogs received prednisone, fecal quality worsened significantly across all treatment groups, with 12 dogs experiencing 30 episodes of outright diarrhea during the study period. These digestive issues are uncomfortable but usually manageable.
The more serious concern is stomach ulceration. Prednisone reduces the production of protective compounds in the stomach lining, leaving it vulnerable to acid damage. A dog with a developing ulcer may vomit (sometimes with blood), lose interest in food, or pass dark, tarry stools, a sign of bleeding in the upper digestive tract. The risk climbs when prednisone is combined with certain pain medications like NSAIDs, a combination most veterinarians avoid for exactly this reason.
Silent Urinary Tract Infections
Prednisone suppresses the immune system, which opens the door to infections the body would normally fight off. Urinary tract infections are particularly sneaky in dogs on long-term steroids. In one study of 71 dogs receiving chronic corticosteroid therapy for skin conditions, 39% had documented urinary tract infections. The troubling part: standard urine sediment analysis alone wasn’t reliable enough to catch them. Because prednisone also masks inflammation, your dog may not show the typical signs of a UTI like straining or frequent small urinations. The increased urination from prednisone itself can further camouflage the problem. Periodic urine cultures are the most reliable way to catch these infections before they spread to the kidneys.
Muscle Wasting and Skin Changes
With prolonged use, prednisone breaks down muscle tissue and inhibits new muscle growth. Dogs develop visible muscle loss, particularly along the hind legs and spine, giving them a pot-bellied appearance as abdominal muscles weaken while the liver enlarges. Larger dogs are hit harder: the odds of developing muscle atrophy increase by about 30% for every additional 5 kilograms of body weight.
The skin thins and becomes fragile. Wounds heal slowly, and some dogs develop secondary skin infections like pyoderma or recurring ear infections. In severe cases, a condition called calcinosis cutis can develop, where calcium deposits form hard, crusty plaques in the skin. These are painful, prone to infection, and slow to resolve even after the medication is stopped.
Steroid-Induced Diabetes
Prednisone forces the body to release more glucose into the bloodstream while simultaneously making cells resistant to insulin, the hormone that normally clears that glucose. In most dogs, the pancreas compensates by producing extra insulin. But if the pancreas can’t keep up, especially in dogs that are already predisposed, full-blown diabetes mellitus can develop. This is more likely with immunosuppressive doses (1.5 mg/kg/day or higher) and prolonged courses. Signs include excessive thirst and urination beyond what prednisone alone would cause, weight loss despite a good appetite, and cloudy eyes from rapid cataract formation. In some dogs, the diabetes resolves when prednisone is discontinued. In others, it becomes permanent and requires lifelong insulin therapy.
Liver Enzyme Spikes
If your vet runs bloodwork while your dog is on prednisone, you’ll almost certainly see elevated liver enzymes, particularly alkaline phosphatase (ALP). This can look alarming on paper, but it’s largely a predictable pharmacological effect rather than a sign of liver damage. Prednisone triggers the production of a specific steroid-induced form of ALP in the liver, kidneys, and intestinal lining. The enzyme levels can rise dramatically, sometimes several-fold, yet the liver tissue itself remains healthy. That said, very prolonged or high-dose steroid use can cause a condition called steroid hepatopathy, where the liver cells become swollen with stored glycogen and the liver physically enlarges. Your vet can distinguish between benign enzyme induction and true liver problems through additional tests if needed.
Behavioral and Mood Changes
Prednisone doesn’t just affect the body. Dogs on corticosteroids often show decreased interest in play and exploration, behaviors associated with positive emotional states. At the same time, irritability and aggression can increase. Some dogs bark more. Others become clingy or restless, unable to settle comfortably.
The appetite surge prednisone causes can also create new behavioral problems. Dogs that were never food-possessive may begin guarding their bowl, counter-surfing, or snapping when food is nearby. If your dog lives with children or other pets, this shift is worth taking seriously. Keeping meals predictable and avoiding unpredictable physical contact during feeding can reduce the risk of a bite incident.
Adrenal Crisis From Stopping Too Quickly
This is arguably the most dangerous risk of prednisone, and it comes not from taking the drug but from stopping it. When a dog receives prednisone for more than a week or two, the adrenal glands scale back their own cortisol production because the medication is supplying it externally. If the drug is withdrawn abruptly, the adrenal glands can’t ramp back up fast enough, leaving the body without adequate cortisol. This is called an Addisonian crisis.
The signs can escalate quickly: weakness, lethargy, vomiting, diarrhea, abdominal pain, and dehydration that progresses to collapse and shock. Hypothermia and a dangerously slow heart rate (seen in about 17% of affected dogs) are red flags. Without emergency treatment, an adrenal crisis can be fatal. This is why prednisone is always tapered gradually rather than stopped cold, giving the adrenal glands time to resume normal function.
Why Dose and Duration Matter
Not all prednisone prescriptions carry equal risk. The dose ranges used in dogs fall into distinct categories: physiologic replacement sits below 0.3 mg/kg/day, anti-inflammatory doses range from 0.5 to 1.0 mg/kg/day, and immunosuppressive doses start at 1.5 to 2 mg/kg/day and go up to 4 mg/kg/day. Most dogs (about 58% in one Australian prescribing survey) receive anti-inflammatory doses, which carry a lower side-effect burden. Only about 10% are prescribed immunosuppressive doses, typically for serious autoimmune diseases.
The concern is that some dogs end up on inappropriately high doses for conditions that don’t require them. In that same survey, 36% of dogs prescribed 2 mg/kg/day or more were being treated for uncomplicated skin and ear problems, conditions that could often be managed with lower doses or alternative therapies. Higher doses over longer periods compound every risk on this list: more muscle loss, greater infection susceptibility, higher diabetes risk, and a longer, more delicate taper when it’s time to stop. If your dog has been on prednisone for weeks and the side effects are worsening, asking your vet about the lowest effective dose or steroid-sparing alternatives is a reasonable conversation to have.