Cortisol is the primary stress hormone produced by your dog’s adrenal glands, two small organs that sit just above the kidneys. It plays a central role in regulating metabolism, immune function, and your dog’s ability to cope with both physical and emotional stress. In healthy dogs, resting cortisol levels typically fall between 0.5 and 4.0 µg/dL, rising and falling naturally throughout the day and spiking during stressful events. Problems start when cortisol stays too high or drops too low for extended periods.
What Cortisol Does in a Dog’s Body
Cortisol affects nearly every system your dog relies on. Its most important jobs include converting stored energy into usable fuel (especially glucose), dialing inflammation up or down, and keeping the immune system in check. During a normal day, cortisol helps your dog maintain steady energy and a balanced metabolism.
When something stressful happens, like a loud thunderstorm or a vet visit, the brain kicks off a hormonal chain reaction. The hypothalamus signals the pituitary gland, which then tells the adrenal glands to release a burst of cortisol. This rapid spike mobilizes energy reserves, suppresses non-essential processes like digestion, and sharpens your dog’s focus on the immediate threat. Once the stressor passes, cortisol levels drop back to baseline. In one study comparing stressed and emotionally healthy dogs, cortisol roughly doubled from a resting average of about 2.0 ng/mL to 4.8 ng/mL after an acute stressor, then returned to normal.
This system works well for short-term challenges. The trouble comes when stress is chronic, like long-term confinement, ongoing anxiety, or disease, and cortisol stays elevated day after day. Sustained high cortisol suppresses the immune system, breaks down muscle, thins the skin, and disrupts the normal balance of blood sugar and fat storage.
Too Much Cortisol: Cushing’s Disease
Cushing’s disease (hyperadrenocorticism) is the most common cortisol disorder in dogs. It happens when the adrenal glands overproduce cortisol, usually because of a small tumor on the pituitary gland or, less often, a tumor on one of the adrenal glands themselves. Middle-aged and older dogs are most frequently affected.
The signs develop gradually and are easy to mistake for normal aging. The most recognizable combination is increased thirst, frequent urination, and a noticeably bigger appetite. Dogs often develop a “pot-bellied” appearance because cortisol redistributes fat to the abdomen and weakens the abdominal muscles. Other visible changes include:
- Skin and coat changes: thinning or fragile skin, hair loss (especially on the trunk), recurrent skin infections, and dark patches of pigmentation
- Activity level: reduced energy, lethargy, and heat intolerance
- Panting: excessive panting even at rest, which is specific to dogs with Cushing’s
- Recurrent infections: urinary tract infections that keep coming back despite treatment
Less commonly, Cushing’s can lead to high blood pressure, blood clots in the lungs, behavioral changes, or vision problems. Because the symptoms overlap with so many other conditions and creep in slowly, many owners don’t realize something is wrong until several signs are present at once.
Too Little Cortisol: Addison’s Disease
Addison’s disease (hypoadrenocorticism) is the opposite problem: the adrenal glands don’t produce enough cortisol, sometimes along with another hormone called aldosterone that controls sodium and potassium balance. It’s less common than Cushing’s but can be life-threatening if missed.
The hallmark symptoms are vague, which is why Addison’s is sometimes called “the great imitator.” In reported cases, 88 to 95% of affected dogs show poor appetite or complete refusal to eat, 85 to 95% are lethargic or depressed, and 68 to 75% experience vomiting. Weight loss, diarrhea, abdominal pain, weakness, and an inability to handle even mild stress round out the picture. These symptoms often wax and wane, improving on their own and then returning, which can delay diagnosis for months.
The most dangerous scenario is an Addisonian crisis, where cortisol and aldosterone drop so low that potassium builds up in the blood and sodium plummets. This can cause a sudden collapse, severe dehydration, and a dangerously slow heart rate. It’s a veterinary emergency.
How Vets Measure Cortisol
A single blood draw can measure your dog’s resting cortisol, but that number alone rarely tells the whole story because cortisol fluctuates throughout the day. Instead, vets use specific tests that challenge the adrenal glands and measure how they respond.
Screening With Baseline Cortisol
A baseline cortisol above 2 µg/dL effectively rules out Addison’s disease. If the result is 2 µg/dL or lower, further testing is needed. This makes a simple blood draw a useful first step when Addison’s is suspected.
ACTH Stimulation Test
This is the most common cortisol test in veterinary medicine. Your dog gets an injection of a synthetic hormone that tells the adrenal glands to produce cortisol at full capacity. Blood is drawn before the injection and again about an hour later. In a healthy dog, the post-injection cortisol lands between 8 and 20 µg/dL. A result above 22 µg/dL points toward Cushing’s disease. A result below 2 µg/dL after stimulation confirms Addison’s disease.
Dexamethasone Suppression Test
This test works in the opposite direction. Your dog receives a low dose of a synthetic steroid that should tell the adrenal glands to stand down. Blood is drawn before the injection and again eight hours later. In a healthy dog, cortisol drops below 1.1 µg/dL. If it stays above 1.4 µg/dL and your dog has the classic symptoms, Cushing’s disease is the likely diagnosis.
Urine Cortisol-to-Creatinine Ratio
This is a screening test you can collect at home by catching a morning urine sample. A ratio below 20 makes Cushing’s very unlikely, which is helpful for ruling it out. A ratio above 20 supports suspicion but doesn’t confirm the diagnosis on its own, because this test picks up nearly every dog with Cushing’s (100% sensitivity) but also flags many dogs who don’t have it (only 22% specificity). It’s best used as a first filter before moving to the more definitive tests above.
What Everyday Stress Does to Cortisol
Not all cortisol problems are caused by disease. Chronic environmental stress, like prolonged isolation, a chaotic household, shelter living, or ongoing conflict with other pets, can keep cortisol elevated enough to affect your dog’s health over time. The physical consequences mirror a milder version of Cushing’s: a weaker immune system, slower wound healing, digestive problems, and changes in behavior or mood.
Short-term stress is normal and healthy. A vet visit, a new environment, or a startling noise will spike cortisol temporarily, and that’s exactly what the system is designed to do. The concern is when the stressor never goes away and cortisol never fully returns to baseline. If your dog is showing chronic signs like recurring skin issues, GI upset, or anxiety-driven behaviors, it’s worth considering whether ongoing stress could be part of the picture.