Steroids cause a predictable set of side effects in cats, starting with increased thirst, urination, and appetite within the first days of treatment. These early changes are nearly universal and usually manageable, but longer courses carry more serious risks including diabetes, hidden infections, skin fragility, and behavioral changes like increased anxiety. What you’ll see depends largely on the dose, the type of steroid, and how long your cat stays on it.
The Most Common Early Side Effects
Almost every cat on corticosteroids will show three trademark changes: drinking more water, urinating more, and acting noticeably hungrier. These tend to appear within the first few days and are dose-dependent, meaning higher doses produce more obvious effects. Weight gain often follows the increased appetite, especially if your cat is free-fed. Some cats also become lethargic or seem less interested in play. Vomiting or nausea can occur but is less common.
These effects typically resolve once the steroid is tapered down or stopped. They’re worth knowing about so you’re not alarmed when your cat empties the water bowl twice a day or starts begging for food constantly.
Infection Risk and Hidden Symptoms
Steroids suppress the immune system, which is often exactly why they’re prescribed for allergies or inflammatory bowel disease. The tradeoff is that your cat becomes more vulnerable to infections. Upper respiratory infections are a particular concern in cats, as steroids can unmask dormant infections that were previously kept in check by the immune system.
Urinary tract infections are especially tricky. Studies estimate that up to 30% of animals on long-term steroids develop latent urinary tract infections. The problem is that steroids also suppress the inflammation that normally signals an infection, so your cat may not show the usual signs like straining to urinate or crying in the litter box. The infection can quietly progress without obvious symptoms, which is why routine urine checks become important for cats on extended steroid courses.
Bacterial skin infections can also develop or worsen. If your cat’s skin condition seems to improve initially but then flares in a different way, a secondary infection may be the cause.
Diabetes Risk
Cats are more prone to steroid-induced diabetes than dogs. Corticosteroids raise blood sugar by making cells less responsive to insulin, and cats already tend toward insulin resistance compared to other species. Overweight cats and older cats face the highest risk.
Signs of diabetes overlap with normal steroid side effects (increased thirst, increased urination), which can make it hard to distinguish. If these symptoms persist or intensify, especially after your cat has been on steroids for several weeks, blood glucose testing can clarify what’s happening. In some cases, steroid-induced diabetes resolves once the medication is stopped. In others, particularly in cats that were already prediabetic, it becomes a permanent condition requiring insulin.
Behavioral and Anxiety-Related Changes
Steroids don’t just affect the body. Research from the University of Pennsylvania found that cats on corticosteroids showed significantly more anxious behaviors than both healthy cats and cats with the same inflammatory conditions who weren’t treated with steroids. Specifically, steroid-treated cats had higher rates of separation-related problem behaviors, compulsive grooming, and other compulsive behaviors like repetitive pacing or apparent hallucinatory responses.
The key finding was that these compulsive behaviors appeared only in cats receiving steroids, not in cats with the same underlying diseases who were treated differently. This strongly suggests the medication itself drives the anxiety rather than the illness. If your cat starts over-grooming, seems more clingy or distressed when left alone, or develops odd repetitive movements while on steroids, the medication is a likely contributor.
Skin and Muscle Changes With Long-Term Use
Cats kept on steroids for months can develop a condition called iatrogenic hyperadrenocorticism, essentially a drug-induced version of Cushing’s syndrome. A study of 12 cats with this condition found progressive skin lesions as the most consistent sign, along with thinning of the skin that makes it fragile and prone to tearing. Other signs included thigh muscle wasting, lethargy, loss of appetite, and increased thirst and urination.
Hair loss (alopecia) and a redistribution of body fat can also occur with prolonged use. The skin changes are particularly important to recognize because fragile skin in cats can tear with normal handling, creating wounds that heal slowly due to the same immune suppression the steroids cause.
Why Cats Get Prednisolone, Not Prednisone
If your vet prescribed prednisolone specifically, there’s a good reason. Prednisone is a prodrug that needs to be converted by the liver into its active form, prednisolone. Cats perform this conversion poorly. A study measuring blood levels after a single oral dose found that prednisolone given directly produced roughly four times higher active drug levels compared to the same dose of prednisone. This means prednisone is largely ineffective in cats, and prednisolone is the standard choice.
Dosing also matters in a way that might surprise you. The same study found that body condition affects drug levels, suggesting that overweight cats may need doses calculated based on their ideal lean weight rather than their actual weight.
Why Steroids Can’t Be Stopped Abruptly
When a cat takes steroids for more than a short course, the body’s adrenal glands reduce their own natural cortisol production because the medication is filling that role. Stopping suddenly can leave the body without enough cortisol, which can cause weakness, vomiting, and in severe cases, a dangerous adrenal crisis.
Tapering typically involves gradually reducing the dose or spacing out doses over days to weeks, giving the adrenal glands time to resume normal function. Your vet will adjust the tapering schedule based on how long your cat has been on steroids and at what dose. The general approach is to reduce the dose in steps, sometimes switching from daily to every-other-day dosing before stopping entirely. Never adjust or discontinue your cat’s steroid dose on your own.
What to Watch For at Home
During short courses of a week or two, expect the increased thirst, hunger, and urination. These are normal and temporary. Keep fresh water available and be prepared for more frequent litter box cleaning.
For longer courses, the signs worth tracking more carefully include:
- Persistent or worsening thirst and urination, which could signal diabetes rather than a routine steroid effect
- Skin changes, including thinning, easy tearing, or new infections
- Behavioral shifts, particularly increased anxiety, compulsive grooming beyond what’s normal for your cat, or new separation distress
- Muscle loss, especially visible in the hind legs
- Signs of hidden infection, such as changes in litter box habits, increased sneezing, or nasal discharge
Cats on long-term steroids generally benefit from periodic blood work and urine testing to catch problems like elevated blood sugar or silent urinary infections before they become serious. How often depends on the dose and your cat’s individual risk factors, but every few months is a common interval for cats on ongoing therapy.