> Add some serotonin/dopamine or related substances and the whole view, the whole attitude changes immediately.

The idea that there is a biological 'switch' underlying depression is misleading. It is in a number of cases but it's only a small percentage.

The crux with depression (and mental health more generally) is that it's a vastly complex phenomenon [1] that we do not fully understand.

We are scoring wins in many battles (e.g. MDMA-assisted therapy) but we are still far away from winning the war.

[1] https://en.wikipedia.org/wiki/Biopsychosocial_model

I don't mean you can cure a depression easily this way. But you can switch it off temporarily and let the patient experience a totally different perspective for at least some moments. In many cases this may help a lot. Many people believe what they see is always what exists and what they feel is always what the situation is. Knowing (as a result of your own experience!) you can have drastically different feelings about the same reality depending on chemicals you ingest change a lot: you know your fear, anger or apathy don't represent the objective reality (nor your self) and you don't have to act the way they push you any more.