Using a radiotracer, [11C]raclopride, that labels dopamine transporters, the team scanned 11 healthy men who took various doses of oral methylphenidate. The results were shocking. "We were surprised as hell," said Volkow. "We didn't expect this." Instead of being a less potent transport inhibitor than cocaine, methylphenidate was more potent. A typical dose given to children, 0.5 mg/kg, blocked 70% of dopamine transporters. "The data clearly show that the notion that Ritalin is a weak stimulant is completely incorrect," Volkow said.