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December 18, 1998
New research shows that methylphenidate (Ritalin) is not likely to become addictive when taken orally and in therapeutic doses. The time it takes drugs to enter the brain and create a reinforcing effect is a key factor.
The study showed that doses of methylphenidate did not reach peak concentrations in the brain until 60 minutes after ingestion, compared with five minutes for cocaine and nine minutes for methylphenidate taken intravenously, according to Nora Volkow, M.D., principal investigator and chair of the medical department at Brookhaven National Laboratory in Stony Brook, N.Y. The study was published in the October American Journal of Psychiatry.
Volkow told Psychiatric News, "The finding is significant because Ritalin can be abused if taken intravenously or snorted. That method of ingestion causes brain concentrations to rise and spike very rapidly, and likely accounts for the high the abuser experiences."
In contrast, "The slow intake of oral doses of methylphenidate into the brain protects against the drug's reinforcing capacity for addiction," said Volkow.
The researchers studied the effects of oral methylphenidate on the brains of seven adult subjects without ADHD by testing a range of weight-adjusted doses (0.25 mg/kg to 1.0 mg/kg), including those used therapeutically.
Because previous research by Brookhaven Laboratory had shown that cocaine, another drug that blocks dopamine transporters, had produced a high in patients when it blocked at least 60 percent of the transporters, Volkow and her colleagues measured levels of dopamine transporter blockade in subjects given methylphenidate to assess whether it would produce a similar high.
Volkow commented, "Using positron emission tomography (PET) scans, we found that methylphenidate is powerful in blocking dopamine transporters and is likely to occupy more than 50 percent of the transporters. This level of occupancy may be necessary for the drug's therapeutic effectiveness."
However, only one subject given oral methylphenidate reported feeling high, which Volkow attributed to the longer amount of time (60 minutes) that the stimulant took to reach peak concentrations in the brain.
In the journal article Volkow and her colleagues acknowledged several limitations of the study including using adults rather than children as subjects, the small group size, and measuring dopamine transporters at 120 minutes rather than 60 minutes, when the peak brain update was observed.