Polyuria and polydipsia are medical terms to describe peeing and drinking more than normal amounts. With polyuria (PU), the body makes more urine than normal, which in turn causes a condition called polydipsia (PD), from Greek polýdipsos "causing great thirst", which means your dog or cat is more thirsty than normal. How much water your pet regularly drinks can vary from day to day, but when a pattern of more than usual intake and outtake occurs, it throws the body out of whack. Finding out the cause involves your veterinarian looking at your pet's patterns and running some tests.

The body systems that control water intake and urine production are the kidneys, pituitary gland and hypothalamus, an area in the front of the brain. Changes in the volume of your blood, which is mostly water, creates a regulatory system to tell these systems how much you should drink and urinate. Causes of PU/PD include low blood pressure, fever, pain, and certain medications. These conditions cause the release of a hormone from the pituitary gland in the brain. This hormone then travels to the kidney to tell your kidneys to keep water in the body. If the kidneys are diseased or damaged, they will lose too much fluid. For example, if blood volume and blood pressure are too low, the hormone is released and the kidneys make less urine. If blood pressure is normal, the pituitary gland does not release the hormone.

Finding the cause for PU/PD can be difficult and require numerous tests. The most common causes in the dog are chronic kidney disease, hyperadrenocorticism (Cushing's), and diabetes. In cats the most common causes are chronic kidney disease, diabetes, and hyperthyroidism. There are other possible causes, including medications like steroids, anti-seizure drugs, and heart disease drugs. To diagnose PU/PD blood tests, urine tests, ultrasounds, and X-rays can be helpful. PU/PD can have many causes, luckily, many of the causes can be successfully managed and the prognosis is generally good.