When rats are treated with Ritalin at an early age, they are more likely to exhibit “behavioral despair” as adult animals, Harvard researchers report.

“The key implication is that Ritalin can have long-term effects on the brain,” lead investigator Dr. William Carlezon told AMN Health.

“There has been some evidence that children who had been treated for attention deficit-hyperactivity disorder (ADHD) with Ritalin and other stimulants, when they grew up they were less likely to abuse drugs,” the investigator explained.

“This was surprising to us, because one of the things that seems to be really reliable in animals is that if you expose them to stimulant drugs like amphetamine or cocaine or opiates and then at a later time test the animals for how much they like the drug, usually the pre-exposure will make them like the drug more,” he added.

To further explore this issue, Carlezon and his colleagues at Harvard Medical School in Boston treated rats with Ritalin during early development, at ages equivalent to 4 to 12 years in humans.

When these rats were exposed to cocaine as adults, they were less sensitive to the drug and exhibited fewer signs of pleasure and reward, according the team’s presentation this week at the annual American College of Neuropsychopharmacology conference in Puerto Rico.

Furthermore, when the animals were forced to swim, “they’ll give up and show us learned helplessness; where instead of trying to escape, they simply float,” Carlezon said.

The researcher does not advise parents to stop giving Ritalin to their children with ADHD.

Instead, he cautions that “it’s really critical to get the proper diagnosis for ADHD in the first place,” before treatment is started.

This involves conducting a full range of tests that measure the attention component, and not just the hyperactivity aspect of the disorder.