I'll just chuck this bit in as it hasn't been mentioned - medium to long term depression / anxiety will lead to a change in your brain chemical make-up.
Therefore, the AD's are necessary to redress that balance and give you the opportunity to be able to talk / deal with the root cause(s).
I've not long started on a low dose of AD's myself, and there's a definate improvement and difference.
I express it as that I should be 6 foot tall (i wish, but anyway...), but I've been squashed down to 5 foot. So I need to be stretched to 6' 6" so that when I stop being stretched, I can return to 6 foot.