ADD is known to have multiple causes.
In addition, evidence also suggests that neurologic, neurochemical, or in some cases, toxic factors may be involved. Other factors, such as medical conditions may exacerbate an existing disorder or contribute to the development of ADD-like problems in some children. Many researchers believe that ADD is due to altered brain chemistry. In 1990 The New England Journal of Medicine published a landmark study directed by Dr. Alan Zametkin at the National Institute of Mental Health which documented the neurological underpinnings of ADD through brain imaging. According to this study, the rate at which the brain uses glucose, its main energy source, was shown to be lower in persons with ADD, especially the portion of the brain that controls movement, emotion, and attention.