What Causes ADHD?

Although ADHD was first identified over a century ago, and is one of the most extensively researched psychiatric disorders, scientists are still unsure what causes ADHD. Research indicates that ADHD is most likely caused by a complex combination of genetic, environmental, and social factors, all of which combine to cause ADHD in a given person.

ADHD is a complex neurodevelopmental disorder. There is no one cause of ADHD. It is not one factor, but a combination of factors, that cause a person to have ADHD.

What Kind of Factors Cause ADHD?

Although there is no singular cause of ADHD, researchers have identified several factors that contribute to the disease. These include certain genes, differences in brain structure and function, and environmental and social factors.

Genetic Causes of ADHD

Research, including twin studies and studies of families with multiple members who have the disease, has shown that ADHD is highly heritable. The fact that ADHD can be shown to run in families suggests that there may be some kind of genetic basis to the disease. However, a complex syndrome like ADHD involves numerous factors, only some of which are genetic. No single distinct gene has been identified as the cause of ADHD.

Although there is no single "ADHD gene", several genetic factors have been strongly linked to ADHD. These include two specific genes called DRD4 and DRD5, and both are involved in the brain's dopamine circuits. Individuals with ADHD show differences in their brain's regulation of dopamine, an important neurochemical associated with pursuing goals and seeking rewards. Another key genetic component associated with ADHD is Chromosome 16. Genetics factors linked to ADHD generally are associated with dopamine regulation, as well as with the structure and function of brain areas important to attention and concentration.

Certain genetic factors, which are inherited, may not be the sole cause of ADHD. They can, however, be shown to predispose some individuals more strongly to developing the disease. While ADHD is not caused solely by genes, there is definitely a genetic component to the disease.

Prenatal and Perinatal Causes of ADHD

In addition to genetics, ADHD has also been linked to certain types of contamination during fetal development. Exposure to certain substances can interfere with brain development, and can affect areas of the brain associated with learning, cognition, attention, and impulse control, becoming a possible cause of ADHD.

Factors during gestation and development that may contribute to causing ADHD include:

• Exposure to nicotine and other toxins from cigarettes, due to the mother smoking while pregnant
• Exposure to alcohol in utero
• Exposure to lead and other heavy metal toxins, either in utero or early in life
• Low birth weight, which can be caused by smoking as well as other factors

It is important that women avoid certain substances, including alcohol and cigarettes, during pregnancy. Exposure to these substances has lasting effects on the development of the child, including increasing susceptibility to ADHD.

Environmental and Social Causes of ADHD

Possible environmental and social causes of ADHD are not yet well understood. It is thought that environment does play a role in ADHD. Some have suggested that factors such as watching television, playing video games, and exposure to social stressors, could all contribute in some way to causing ADHD.

Studies have indicated a higher prevalence of ADHD in children from single-parent homes, from low-income households, or otherwise from family environments that may be stressful and inconsistent. Although the link is not yet well understood, this does indicate that the family environment may be a cause of ADHD.

One frequently suggested factor in in causing ADHD, has been television viewing among children. For the most part, television shows tend to feature many flashing, moving images, at a very fast pace. Some researchers have suggested that exposure to fast-paced TV images during early childhood could contribute to "rewiring" the brain to process brief information at a fast pace. This could interfere with ability to process more complex information over longer periods of time, such as the information in a textbook chapter or classroom lecture. It is not yet clear whether television causes ADHD, or whether children already disposed to ADHD are more likely to watch television. Still, many professionals advise that parents limit television viewing by children, especially very young children.

Along with television viewing, video games have also been proposed as a possible factor in causing ADHD. Like television, video games move at a fast pace. Video games also offer rewards-- getting to the next level or winning a new power-up-- in the short-term, a process which acts on the brain's dopamine circuits and results in feelings of pleasure. This may affect children's ability to handle situations, like learning in a classroom, that require longer periods of concentration, and which have delayed rewards.

The influence of social and environmental factors, including family environment and media exposure, on ADHD, is not entirely understood yet. Although watching television or playing video games are probably not, in themselves, enough to cause ADHD, there is evidence that these behaviors may contribute to the disorder.

So Does Anyone Know What Causes ADHD?

No one knows for sure what exactly causes ADHD. Scientific research has indicated a number of factors that appear to contribute to the disease. ADHD is most likely caused by a complex interplay of environmental, social, and genetic factors, which come together in certain ways to form the set of behaviors and characteristics that constitute ADHD.

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