The core experiences of depression – changes in energy, activity, thinking and mood – have been described for more than 10,000 years. The word “depression” has been used for about 350 years. Given this long history, it may surprise you that experts don’t agree about what depression is, how to define it or what causes it. But many experts do agree that depression is not one thing. It’s a large family of illnesses with different causes and mechanisms. This makes choosing the best treatment for each person challenging. Reactive vs endogenous depressionOne strategy is to search for sub-types of de…