Stimulant Inaction: ADHD drug’s mental lift proves surprisingly weak

Children with attention-deficit hyperactivity disorder (ADHD) often calm down and behave better when taking the stimulant medication methylphenidate. Nonetheless, this drug largely fails to alleviate underlying mental difficulties considered crucial to ADHD, a new study finds.

Methylphenidate, better known as Ritalin, leaves intact a shortage of “executive” mental functions that many researchers suspect elicit ADHD-related behavior problems, say psychiatrist David R. Coghill of the University of Dundee, Scotland, and his colleagues. Executive-functioning tests focus on the ability to ignore distracting information, manipulate information in one’s head, and shift attention from one attribute of an object to another.

“Even following clinical improvement with methylphenidate, there remain unaffected [neuropsychological] deficits,” Coghill says.

In contrast, the researchers hold, stimulant treatment aids performance on a few basic memory tasks, such as tests of the ability to recognize a previously presented abstract pattern in a set of choices or to remember spatial locations of items in a previously observed scene.

The new study appears in the Nov. 1 Biological Psychiatry.

Coghill’s team studied 75 boys, ages 7 to 15, diagnosed with ADHD at an outpatient psychiatric clinic. Participants received three treatments in different orders, each for 1 month: low-dose methylphenidate, high-dose methylphenidate, and placebo pills. Neither the boys nor the researchers knew which treatment a participant was receiving at a given time.

A majority of the youngsters behaved better during one or both of the drug treatments, according to parent and teacher reports.

Yet in testing on a battery of mental abilities before and after each phase of treatment, methylphenidate produced gains only in basic visual memory and in the ability to identify target images while ignoring distracting images. Even on the latter task, a simple probe of executive functioning, boys with ADHD performed as well, before the study, as boys with no psychiatric disorders did.

Stimulant treatment offered no benefits in complex tests of executive function, such as the ability to recall information needed to achieve a goal.

The study “raises questions about the effects of chronic stimulant treatment [on ADHD],” comment psychologist Scott H. Kollins and psychiatrist John S. March, both of Duke University Medical Center in Durham, N.C., in an accompanying editorial.

A related investigation, published in the August Journal of the American Academy of Child & Adolescent Psychiatry, suggests that clinical benefits of stimulant treatment diminish over time. Psychiatrist Peter S. Jensen of Columbia University and his coworkers tracked 485 boys and girls with ADHD who received 14 months of intensive treatment with stimulants, behavior therapy, a combination of both, or routine community care.

Children who received medication showed the most improvement in ADHD symptoms. However, their behavioral advantage disappeared 2 years after completion of treatment.

The researchers also found that children with ADHD were taller and heavier than expected for their age before treatment but then showed stimulant-related decreases in growth rate. Three years of stimulant treatment stunted growth by almost 1 inch and by more than 4 pounds, they estimate.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.