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William Carlezon talks about the ADHD research he conducted with Susan Anderson, in which they tested the effects of Ritalin on rats.

Between 3 and 12% of school-age children may suffer from attention-deficit hyperactivity disorder. Known by the acronym ADHD, the condition manifests itself with inappropriate impulsivity, lack of attention and in some cases, hyperactivity. Fortunately, the prescription drug Ritalin can ease ADHD's symptoms. But since ADHD is difficult to diagnose accurately, doctors wonder what effect Ritalin might have on patients wrongly diagnosed with the disorder.

New research by scientists from Harvard-affiliated McLean Hospital and the National Institutes of Health, presented at the annual meeting of the American College of Neuropsychopharmacology, provides a preliminary answer. It suggests that the misdiagnosis of ADHD followed by treatment with Ritalin may lead to a risk that the patient might develop depression in adulthood.

William Carlezon and Susan Anderson tested the long-term effects of Ritalin on normal juvenile rats aged between 4 and 12 in equivalent human years. Carlezon exposed the rats to twice-daily doses of Ritalin. As the rodents reached adulthood, they had a lower than normal response to pleasure or reward. Scientists test a rat's response to rewarding things such as, food, sexual behavior, cocaine or electrical brain stimulation. Rats exposed to Ritalin in the developing years had a lower than normal response to these stimuli.

Carlezon has also found that the Ritalin treated rats were more likely to show despair-like behaviors in stressful situations. To test this, the rats are placed in large water tanks. The scientists measure the amount of time the rat spends trying to find a way out. If a young rat is exposed to Ritalin then tested as an adult, it will spend less time trying to get out, and float passively in the water.

Even though these initial findings are from studies done on rats, the doctors extrapolate that stimulants like Ritalin may have long-term consequences on normally functioning human brains. Patients with true ADHD may have a different chemical make up, and more research is needed to determine Ritalin's effect on an individual with ADHD. This research is most relevant for those misdiagnosed with ADHD, and underscores the importance of finding a reliable way to diagnosis ADHD before a physician prescribes Ritalin.

This project is supported by a Science Education Partnership Award (SEPA) from the National Center for Research Resources, National Institutes of Health. It does not necessarily represent the official views of NCRR or NIH.