Lead author Helga Zoega, a post-doctoral fellow of epidemiology at Mount Sinai's Institute for Translational Epidemiology, and colleagues at Mount Sinai School of Medicine and University of Iceland analyzed data from the Icelandic Medicines Registry and the Database of National Scholastic Examinations.
The study involved 11,872 Icelandic children born in 1994 to 1996. The children started medication for ADHD at different times between fourth- and seventh-grades.
The findings, published in the journal Pediatrics, showed children who began drug treatment within 12 months of their fourth-grade test declined 0.3 percent in math by the time they took their seventh-grade test, compared with a decline of 9.4 percent in children who began taking medication 25 to 36 months after their fourth-grade test.
"Children who began taking medications immediately after their fourth-grade standardized tests showed the smallest declines in academic performance," Zoega said in a statement. "The effect was greater in girls than boys and also greater for children who did poorly on their fourth grade test."