[NickM]

Oh yeah, certainly, being depressed is correlated with all kinds of changes in biology. I'm not saying it's like "just in your head", but the question is, do those changes lead to being depressed or does being depressed lead to biological changes?

Of course that question is an oversimplification since the answer is certainly some of both; but the prevailing wisdom seems to be that it's mostly/all biological changes leading to feeling depressed, whereas I'm not convinced the scales don't lean more in the other direction, at least on average.

EDIT: but as to your point about stress leading to elevated cortisol levels, to me that's clearly not a biological cause. The cause is stress, and the elevated cortisol levels are an effect of the stress. It's not like the hormone levels just went up all by themselves due to some genetic abnormality or something; if they did, then yeah maybe that's a biological disease that warrants some kind of chemical correction, but that's not at all what we're talking about.