While no one really knows what causes ADHD, it is generally agreed by the medical and scientific community that ADHD is biological in nature. Many believe that it results from a chemical imbalance in the brain.

Events in the past have provided insight into what may be happening in the brains of children with ADHD:

In 1937, a Rhode Island paediatrician reported that administering stimulants to hyperactivity/inattentive children had the unexpected effect of calming them down. Today, stimulants (such as Ritalin) have become widely used in the treatment of ADHD children. It is suspected that stimulants works through the release of powerful chemical messengers in the brain called neurotransmitters. Brain cells, or neurons, do not actually connect to each other - there is a gap between them. Neurotransmitters are passed between neurons (see the picture on the right), and this is how neurons communicate with each other. Many researchers have suspected that ADHD may result from a problem associated with this communication between neurons. If you wish to read more on the neurobiology (what is happening in the brain) possibly underlying ADHD, Click here.

This curious reaction to stimulants suggests that there is a difference between the brains of ADHD and non-ADHD people. In trying to understand this difference, researchers have mainly focused on two possible causes:

• 1. Genetics
• 2. Environmentally (or non-genetic) causes

Here we present summaries of both, plus additional theories of causality.

1. Genetics

A lot of todays research suggests that genetics plays a major role in ADHD. one journal article suggests ADHD has a heritability of 0.75 to 0.91.
(1.0 = totally genetic, while 0.0 = absolutely not genetic).

The possibility of a genetic cause to ADHD is further supported by the fact that ADHD appears to run in families. Between 10 and 35 percent of children with ADHD have a first-degree relative with past or present ADHD. Approximately half of parents who have been diagnosed with ADHD themselves, will have a child with the disorder.

A large number of twin studies also suggest a genetic element to ADHD. If ADHD is present in one twin, it is significantly more likely also to be present in an identical twin than in a fraternal twin. Even when these twins have been raised separately.

If you wish to read more thorough articles concerning possible genetic causes of ADHD, have a look at our Academics page.

2. Environmentally (or non-genetic) causes

Investigators have suggested that some of the following could be responsible for ADHD symptoms:

• exposure to toxins (such as lead)
• Complications during pregnancy - such as oxygen deprivation.
• Low birth weight (less than 1500 grams (3.3 pounds)).
• Low Omega-3 essential fatty acids

All of these possibilities need further research however.

PARENTS PLEASE STOP SMOKING - THINK OF YOUR CHILDREN

Everyone knows that mothers should not smoke during pregnancy, but recent scientific papers have also suggested that prenatal smoking may play a role in causing ADHD. Studies have found that children of mothers who never smoked have less chance of having a learning disability and hyperactivity.

If you wish to read more thorough articles concerning possible non-genetic causes of ADHD, have a look at our Academics page.

Other possible causes

According to the National Institutes on Health, ADHD is not usually caused by:

• Too much TV
• Sugar
• Caffeine
• Food colourings
• Poor home life
• Poor schools

Food allergies and additives There is a strongly held belief by some people that additivtes and food allergies cause the behavioural symptoms of ADHD. A review of carefully conducted scientific studies has suggested that only 5% of ADHD children show any behavioural or cognitive improvement (the improvements that were observed were not as dramatic as those seen in response to stimulant medication). This finding suggests that for the vast majority of ADHD children additives and food allergies may not play a major role in causing ADHD. Studies have generally focused mainly on the KaiserPermanente and Feingold diets. While we point out that there is little evidence to support the "additives and food allergy" theory of ADHD, if you are interested, have a look at the Feingold website. There are also books available on the market: Feingold's Cookbook for Hyperactive children, by B. Feingold. Why your Child is hyperactive, by B. Feingold. Your Child's behavior chemistry, by L. Smith.