There are many researchers who are not even sure what it is that causes depression. Many believe we now have more reasons than one, the source for depression symptoms and consequently leads to depression. The first main reason that the researchers believe causes depression, the physical changes inside the brain of the form in the Depression. Hormone levels are supposedly not in a very reasonable balance. Part of the real reason for the depression is the physical nature on the changes that occur within one's body. But most of it is caused by the chemical changes in the entire body.