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Dopamine is the neurotransmitter associated with prediction of reward (aka desire/craving/addiction). Serotonin is very complex (in humans) but more about social-emotional processing.

Dopamine is the neurotransmitter you’re thinking of. And also glutamate since glutamatergic firing in brain reward pathways are heavy associated with addiction

[beambot]

My bad. You're absolutely right: Dopamine, not serotonin.