But questions continued to be raised, especially concerning the drugs’ mechanism of action and the durability of effects. Ritalin and Adderall, a combination of dextroamphetamine and amphetamine, are stimulants. So why do they appear to calm children down? Some experts argued that because the brains of children with attention problems were different, the drugs had a mysterious paradoxical effect on them.

However, there really was no paradox. Versions of these drugs had been given to World War II radar operators to help them stay awake and focus on boring, repetitive tasks. And when we reviewed the literature on attention-deficit drugs again in 1990 we found that all children, whether they had attention problems or not, responded to stimulant drugs the same way. Moreover, while the drugs helped children settle down in class, they actually increased activity in the playground. Stimulants generally have the same effects for all children and adults. They enhance the ability to concentrate, especially on tasks that are not inherently interesting or when one is fatigued or bored, but they don’t improve broader learning abilities.

And just as in the many dieters who have used and abandoned similar drugs to lose weight, the effects of stimulants on children with attention problems fade after prolonged use. Some experts have argued that children with A.D.D. wouldn’t develop such tolerance because their brains were somehow different. But in fact, the loss of appetite and sleeplessness in children first prescribed attention-deficit drugs do fade, and, as we now know, so do the effects on behavior. They apparently develop a tolerance to the drug, and thus its efficacy disappears. Many parents who take their children off the drugs find that behavior worsens, which most likely confirms their belief that the drugs work. But the behavior worsens because the children’s bodies have become adapted to the drug. Adults may have similar reactions if they suddenly cut back on coffee, or stop smoking.

TO date, no study has found any long-term benefit of attention-deficit medication on academic performance, peer relationships or behavior problems, the very things we would most want to improve. Until recently, most studies of these drugs had not been properly randomized, and some of them had other methodological flaws.

But in 2009, findings were published from a well-controlled study that had been going on for more than a decade, and the results were very clear. The study randomly assigned almost 600 children with attention problems to four treatment conditions. Some received medication alone, some cognitive-behavior therapy alone, some medication plus therapy, and some were in a community-care control group that received no systematic treatment. At first this study suggested that medication, or medication plus therapy, produced the best results. However, after three years, these effects had faded, and by eight years there was no evidence that medication produced any academic or behavioral benefits.