I usually take out 8 or so for the average depressed person. It gives me a starting point. Acute depression is often helped but because the condition causing it may still exist, results are not as good. This may require professional help or even drugs. I'm not sure ALL depression is psychological, but certainly most of it is.
Emotions come out of the subconscious mind.
Therefore the subconscious must be REprogrammed to effect a cure. Depression may be self-induced, in a period of acute grief. It hangs on in Pavlovian fashion. That it is a disease is simply an excuse made by inept therapists. A rapid cure requires outside intervention in some form, and there are many ways of doing it with varying degrees of effectiveness.