What is Cushing's Disease? It's a common disease on older dogs that can lead to diabetes if left untreated. It's an over production of cortisol which is a hormone produced by the Adrenal Glands. Cortisol is one of the hormones responsible for healthy skin and energy (although there are several other factors as well.) Signs of this disease can be as follows: increased thirst and urination, hair loss, lethargy etc... Though it can be difficult to diagnose, testing is available to make diagnosing or ruling out much easier.