Cushing’s disease is a hormonal disorder in which a dog’s body produces too much cortisol, the stress hormone that normally helps regulate metabolism, immune function, and blood sugar. About 80 to 85 percent of cases are caused by a small, usually benign tumor on the pituitary gland at the base of the brain, which sends constant signals to the adrenal glands to keep producing cortisol. The remaining 15 to 20 percent are caused by a tumor on one of the adrenal glands themselves. It most commonly appears in middle-aged and older dogs, typically those over six years old.
How Excess Cortisol Affects the Body
Cortisol plays a role in nearly every organ system, so when levels stay chronically elevated, the effects are widespread. The hormone triggers the liver to store more fat and break down muscle protein, which is why one of the hallmark signs is a swollen, pot-bellied abdomen. That belly isn’t just fat redistribution. The abdominal muscles weaken and the liver enlarges, pushing the belly outward. At the same time, cortisol suppresses the immune system, making dogs more prone to skin infections and urinary tract infections.
Cortisol also interferes with how the kidneys concentrate urine. Dogs with Cushing’s disease often drink dramatically more water than normal and urinate far more frequently, sometimes having accidents indoors after years of being housetrained. Appetite increases noticeably too. These three signs together, excessive thirst, excessive urination, and a ravenous appetite, are the most common reasons owners first bring their dog to the vet.
Signs to Watch For
The symptoms of Cushing’s disease develop gradually, often over months, which is why many owners initially attribute them to normal aging. Beyond increased thirst, urination, and hunger, common signs include:
- Hair loss: Typically symmetrical on both sides of the body, often starting on the flanks and trunk while sparing the head and legs
- Thin, fragile skin: The skin may bruise easily or heal slowly from minor wounds
- Pot-bellied appearance: A sagging abdomen caused by muscle wasting, fat redistribution, and liver enlargement
- Panting: Excess cortisol redistributes fat to the chest and abdomen, making breathing harder
- Lethargy and muscle weakness: Dogs may struggle with stairs or seem less interested in walks
- Recurring skin or urinary infections: A weakened immune system makes infections more frequent
Because these changes creep in slowly, it can help to compare recent photos of your dog to pictures from a year or two ago. The physical changes are often more obvious in side-by-side comparison.
Pituitary vs. Adrenal Cushing’s
The distinction between pituitary-dependent and adrenal-dependent Cushing’s matters because it affects treatment options and outlook. In pituitary-dependent cases, the far more common form, a tiny tumor on the pituitary gland overproduces a hormone called ACTH, which tells the adrenal glands to churn out cortisol. Both adrenal glands enlarge in response. Most of these pituitary tumors are small and slow-growing, though a small percentage grow large enough to press on the brain and cause neurological symptoms like disorientation or circling.
In adrenal-dependent cases, a tumor on one of the adrenal glands produces cortisol on its own, independent of pituitary signals. About half of adrenal tumors are benign and half are malignant. The malignant ones can invade nearby blood vessels or spread to other organs, which makes imaging (usually an ultrasound or CT scan) important for surgical planning.
A Third Cause: Steroid Medications
There’s also a form called iatrogenic Cushing’s syndrome, which isn’t a disease at all but rather a side effect. Dogs that receive corticosteroid medications (like prednisone) for allergies, autoimmune conditions, or inflammatory diseases can develop identical symptoms if the medication is used at high doses or over long periods. The treatment is to gradually taper the steroid under veterinary supervision, not to stop it abruptly, since the adrenal glands need time to resume normal cortisol production.
How Cushing’s Disease Is Diagnosed
Diagnosing Cushing’s can be frustrating because no single test is perfectly accurate, and results sometimes need to be repeated. Vets typically start with blood work and a urinalysis, which may show elevated liver enzymes, high cholesterol, or dilute urine. These findings raise suspicion but don’t confirm the diagnosis. From there, two main hormone tests are used.
The low-dose dexamethasone suppression test is the most commonly recommended screening test. Your dog receives a small injection of a synthetic steroid, and blood samples are drawn at 4 and 8 hours afterward. In a healthy dog, the injection signals the body to temporarily reduce its own cortisol production. In a dog with Cushing’s, cortisol levels stay elevated despite the signal. If the 8-hour cortisol level remains above a certain threshold, the result supports a Cushing’s diagnosis. This test can also sometimes help distinguish between pituitary and adrenal forms based on whether cortisol partially drops at the 4-hour mark.
The ACTH stimulation test works differently. Your dog receives an injection of synthetic ACTH, the hormone that tells the adrenal glands to produce cortisol. A blood sample is taken one hour later. If cortisol spikes unusually high, it suggests the adrenal glands are overactive. This test is less sensitive for adrenal tumors, missing up to 41 percent of adrenal-dependent cases, but it’s the only test that can identify iatrogenic Cushing’s caused by steroid medications. An abdominal ultrasound is often added to look at the size and shape of the adrenal glands and check for tumors.
Treatment Options
For pituitary-dependent Cushing’s, the most common approach is daily medication to reduce cortisol production. The standard drug works by blocking an enzyme the adrenal glands need to manufacture cortisol. The typical starting dose depends on body weight, and many vets begin conservatively and adjust upward based on follow-up testing. The goal isn’t to eliminate cortisol entirely (dogs need some to survive) but to bring it back into a normal range.
An older medication takes a more aggressive approach by actually destroying layers of adrenal gland tissue. It’s effective but carries a higher risk of side effects, including the possibility of dropping cortisol too low and causing an adrenal crisis. For this reason, the enzyme-blocking drug has become the more popular first choice.
For adrenal tumors, surgery to remove the affected gland is often the best option if the tumor hasn’t spread. Success rates are high: in a study of 70 dogs, over 95 percent survived to go home after surgery, and the 1-year survival rate was 92 to 95 percent regardless of the surgical technique used. The 3-year survival rate ranged from 81 to 89 percent. However, adrenal surgery is complex and carries risks including blood pressure swings and blood clots during the procedure, so it’s typically performed by a veterinary surgeon with specialized training.
Surgical removal or radiation of pituitary tumors is possible at certain specialty centers and carries an average survival time of 2 to 5 years, though these procedures are less widely available and more expensive than medical management.
Ongoing Monitoring
Cushing’s disease isn’t cured by medication; it’s managed. That means regular veterinary visits and blood work for the rest of your dog’s life. After starting medication, the first follow-up hormone test is typically done 10 to 14 days later, timed 4 to 6 hours after the morning dose. Any time the dose is adjusted, another test follows 10 to 14 days after the change.
Once your vet finds a dose that’s working well, testing moves to 30 days, then 90 days, and then every 3 months going forward. Between visits, you’ll want to watch for signs that cortisol has dropped too low, which can be a medical emergency. Symptoms of too little cortisol include loss of appetite, vomiting, diarrhea, weakness, and collapse. If you notice these, stop the medication and contact your vet immediately.
What to Expect Long-Term
With treatment, many of the most bothersome symptoms improve within the first few weeks to months. Excessive drinking and urination are usually the first to resolve, followed by gradual improvements in energy, skin, and coat quality. Hair regrowth can take several months. The pot-bellied appearance may improve but doesn’t always fully resolve, particularly in dogs who have had the disease for a long time before diagnosis.
Medical therapy for pituitary-dependent Cushing’s carries an average survival time of about 2 to 2.5 years from diagnosis. One study of dogs treated with twice-daily medication found a median survival of roughly 2.7 years, with some dogs living nearly 5 years. These numbers reflect the fact that most dogs are already middle-aged or older at diagnosis and may eventually pass away from unrelated causes. Many dogs with well-managed Cushing’s maintain a good quality of life for the remainder of their years, continuing to enjoy walks, meals, and time with their families in comfort.