One was given a dopamine agonist drug beforehand, suppressing the level of dopamine in their brains; the other was given dopamine precursor L-dopa, effectively increasing their dopamine levels.

But too much dopamine can have the opposite effect—demotivating us and impairing our ability to self-regulate. This is the dopamine overload state that characterizes addiction (Zald, 2023).

Addiction Drugs of Abuse Cause Addiction Through Effects on the Brain Fifty years of research studies show that all drugs change dopamine systems. Posted June 19, 2025 | Reviewed by Gary Drevitch ...