The placebo effect and depression. This sounds like a perfect time to live in the present if you're disturbed by the past and future. — Question
I agree, though maintaining a present focus can be very unpleasant when in the grip of mental illness. The underlying cause of depression can be based in past experience, but working at a subconscious level, leaving you with a miserable present experience, with no obvious immediate cause. The tendency is to try to escape the present through various means, be it excessive sleeping, alcohol and drugs, television, video games, or other activities requiring little motivation and effort.
is the depression causing the anxiety or the anxiety causing the depression? — Question
Though I have little experience with anxiety, I could imagine how having to deal with it for an extended period of time could lead to depression. Left untreated, with no resolution in sight, it is easy to see how someone could start to have feelings of hopelessness.
Having experienced major depression for several years, without developing problems with anxiety, I doubt that a strong causal relationship exists in that direction. When depressed, the tendency is to shut down and escape the present. There isn't much of a future focus, aside from the loss of hope regarding positive change.
As for the placebo effect, I can see how it could apply to someone in a depressed state. For example, telling someone they are being given an effective antidepressant, and instead substituting a sugar pill. The expectation and hope tied to the possibility of recovery could have an effect on the brain's functioning, even though there has been no real change in present circumstances.