But that's sort of is my point, it's all statistical, that's why they have medical trials for years before FDA approves new drugs. We sort of know what is happening in the brain, it's lacking one neurotransmitter or the other and all the drugs/supplements basically either provide it or pretend to be one. Another approach I've seen is to stimulate certain hormones, but again it's individual because some people might have excess of one hormone and lack of the other. Relaxation and meditation is basically natural way to balance certain hormones (reduce cortisol in particular). Or sun exposure gives you vitamin D (which is technically a hormone) and it's been studied to help with depression, but some people need more of it than others etc. I recommend you to pick up a book on nutrition before jumping into this space, one of the easy to read books is Ultramind Solution by Dr Hyman. Hope this helps.