Normally, our brain cells cycle and reuse hormones like serotonin and dopamine, which play critical roles in how we experience desire, motivation, pleasure, and reward. After they're released by brain cells to send out their signal, they're taken up again by special receptors on that cell. Cocaine blocks those receptors, effectively shutting off this normal cycling process. The result? A glut of the hormones that key our feelings of desire, behavior reinforcement, and pleasure (AKA a "high").