 PTSD causes biochemical changes in the brain and body, that differ from other psychiatric disorders such as major depression.Individuals diagnosed with PTSD respond more strongly to a dexamethasone suppression test than individuals diagnosed with clinical depression.Most people with PTSD show a low secretion of cortisol and high secretion of catecholamines in urine, with a norepinephrine/cortisol ratio consequently higher than comparable non-diagnosed individuals.