Chronic cocaine use causes physical changes in the brain's reward circuitry, leading to drug tolerance.

The human brain is highly adaptable. When repeatedly flooded with massive, artificial surges of dopamine, it attempts to protect itself by reducing the number of available dopamine receptors or dulling its sensitivity. As a result, the natural reward system becomes severely compromised. The user no longer experiences the same level of pleasure from normal activities, or even from the drug itself, driving them to take larger and more frequent doses to achieve the same effect.