[mtdewcmu]

There's also a such thing as chronic depression, and reason to think that major depression follows a relapsing-remitting course, at least in some people, and may turn into or be a warning sign of developing chronic depression.

Which says nothing about the effectiveness of psychiatric treatments. But it does argue for aggressive early treatment, whatever that might mean, in the hope of halting the progression before it could become chronic.

Mental illness is fundamentally hard to study scientifically, and I'm not convinced that any of the treatments we have actually work. But it's humane to make the attempt.