Cocaine increases levels of the natural chemical messenger dopamine in brain circuits related to the control of movement and reward. Normally, dopamine recycles back into the cell that released it, shutting off the signal between nerve cells. However, cocaine prevents dopamine from being recycled, causing large amounts to build up in the space between two nerve cells, stopping their normal communication. This flood of dopamine in the brain’s reward circuit strongly reinforces drug-taking behaviors. With continued drug use, the reward circuit may adapt, becoming less sensitive to the drug. As a result, people take stronger and more frequent doses in an attempt to feel the same high, and to obtain relief from withdrawal.