One of the most important neurochemicals to regulate with behavior.
Dopamine is the chemical that drives pursuit, it is literally the life giving spark in all animals.
Dopamine doesn’t make us feel pleasure, it makes us pursue things. When we get pleasure without pursuit, aka heroin, drugs, porn-fueled masturbation, etc., it messes up our dopamine system. Dopamine gets jacked up in anticipation of easy pleasures, then crashes afterwards, preventing us from pursuing other things.
It leads to depression. The body doesn’t experience the pain of pursuit, so it starts to raise the dopamine baseline until we only get pleasure from these specific activities.
“Addiction is a gradual narrowing of the things that bring us pleasure.”
A fulfilled life is probably the opposite, where we can find pleasure from doing any action or pursuing any goal, rather than just a narrowly-defined set of goals, e.g. smoke weed and eat french fries.