When I was a lead investigator in the pharmaceutical industry, for a few years I worked on antidepressants. The idea was to target the machinery that affects levels of neurotransmitters (serotonin, dopamine, norepinephine), aiming to elevate mood-enhancing substances, usually very subtly.
Prozac, for example, is an SSRI, for selective serotonin re-uptake inhibitor. The idea is to nudge serotonin levels a little higher. Why does it work for depression? It's unclear. Are all things that boost serotonin very good antidepressants? No.
You never know how the brain reacts until you try it. You need to "jangle the wires and see the result" as my boss used to say.
Modulating different combinations of serotonin, dopamine, norepinephine give different results- useful in some cases for addictions, OCD, etc.
Brain chemistry is hard.