I'm pleased to see the spirited posts above. To be honest, I thought that PC members would, by and large, be in support of the "Chemical Imbalance" theory. I would encourage people who like the theory to post also. Here is a link that is supportive of the "Chemical Imbalance" theory:

Depression’s Chemical Imbalance Explained | Psych Central News

One of the things that I've found repeatedly in my reading is that this debate can become a case of "Which came first - the egg, or the chicken?" In other words, maybe becoming depressed makes the levels of serotonin and other neurotransmitters drop, rather than vice versa.

I think that the things we learn, or fail to learn, can affect out ability to deal with the tough breaks in life. That doesn't imply that brain chemicals can't also be factors, but I think the "Imbalance" theory caused a lot of people to believe that depression had more to do with physical causes than with anything else. That might have been leaping to more of a conclusion than the science supports.

I'm hardly an indifferent by-stander. I have bad depression, and I've become disillusioned with medication as a solution. Many years ago, amitriptyline dramatically improved my life, and I still take it. For two years, though, I've been getting more and more depressed. Pdocs have prescribed med after med after med. None of them helped, and I've stopped them all, except the amitriptyline.

I strongly believe there are a lot of causes for depression that have to do with the experiences you have in life. What say you?