I am not endorsing these hypotheses, but they are interesting to ponder:

• Depression is neither disease nor disorder rather an adaptation that evolved to serve a purpose

• Depression is so much more prevalent than currently recognized that it is “species typical”

• Antidepressants drive neurotransmitter levels so high that homeostatic regulation kicks in

• Antidepressants may suppress symptoms in a manner that increases risk for subsequent relapse

• Cognitive therapy works by making rumination more efficient and “unsticking” self-blame

• Adding antidepressants may interfere with any enduring effect that cognitive therapy may have

Those are from a new paper by Steven D. Hollon.