The interesting bit here is that literally everything you do or eat affects this. For example your diet is going to get broken down into micronutrients and for

The interesting bit here is that literally everything you do or eat affects this. For example your diet is going to get broken down into micronutrients and for a lot of these molecules, while they are circulating, there are a lot of receptors that they are going to bind to and modify function on. And then there is exercise (or lack thereof) and all of the even-further away components (personal relationships, sleep etc) work on your brain and state of mind too. When I was in Med school I came across this joke - apparently the effect size of antidepressants decreases with phase 3 trials, trending back to placebo. So the joke goes that as soon as a new antidepressant comes out, they need to use it before it stops working. The deeper question here is whether the initial effect size was simply due to chance, and so the effect size of antidepressants is simply placebo and it was poor studies that let them get in the wild in the first place