These findings, published in Pediatrics, may be surprising to parents because drugs such as Ritalin or Adderall used to treat ADHD can suppress appetite, said Dr. F. Xavier Castellanos, the study co-author and a professor of child and adolescent psychiatry at New York University.
"It's not uncommon for kids treated with ADHD medications to be fairly thin," Castellanos said. Because parents often worry that thinner boys won't grow as tall, "sometimes [they] will encourage their boys to eat more."
Instead, to help avert weight problems down the road, parents should be alert to poor eating habits. "If anything, you have to pay attention to how many times they're having fast food, how many times they're having fried food, whether they're getting meals supersized," Castellanos said.
The study comes at a time when ADHD rates are rising. A new report from the Centers for Disease Control and Prevention found that ADHD is the most common mental health issue in children ages 3-17, with nearly 7 percent of kids receiving a diagnosis.
The NYU researchers followed 222 boys -- 111 with ADHD and 111 without, for an average of 33 years -- hoping to better understand the disorder's effects on the brain. The boys with ADHD, all from middle-class, white families, were diagnosed between the ages of 6 and 12.
Decades later, when some of the men returned for brain scans, many of the now 40-something adults who had ADHD as children had gained so much weight they barely fit into the fMRI machine, Castellanos said.
Image: Boy eating, via Shutterstock