From the link provided below, article by Volkow, re: cocaine and Ritalin in the brain (Eight healthy male subjects, 20 to 51 years of age): For both drugs, their fast uptake in striatum paralleled the experience of the "high." For methylphenidate, the high decreased very rapidly despite significant binding of the drug in the brain. In contrast, for cocaine, the decline in the high paralleled its fast rate of clearance from the brain. We speculate that because the experience of the high is associated with the fast uptake of cocaine and methylphenidate in the brain, the slow clearance of methylphenidate from the brain may serve as a limiting factor in promoting its frequent self-administration.