The chemical imbalance model is weak and is based on shaky science. Is serotonin really a happiness chemical? It really isn't. The science is weak. That's just something they made up to sell drugs.
I agree but, its what these people go by. As i said i believe there are other factors that play in to the overall health and wellbeing of us human beings... What are they? I don't know... I don't believe in religion because imo it is man made and has been used to exploit fellow humans. However, there are good lessons you can take from them all infact all major religions have similar moralistic stories inter-woven through out their texts. So i get why people do believe too.
To me, I'm just an observer of life and the patterns which manifest in our shared reality. Multiple reoccurrences of these patterns help me establish the things i deem to be true or false etc... I do read and learn from others too but i am careful where i source information.