ADHD, as it is known today, is defined as being "a neurobiological disorder that interferes with an individual’s ability to regulate activity level and behaviour, and sustain focus on tasks in a developmentally appropriate way" .
In individuals with ADHD, lower than normal levels of certain neurotransmitters (substances that transmit signals between nerve cells) are present in the regions of the brain that are responsible for regulating attention, impulsivity and hyperactivity . Typically, a child with ADHD struggles to stay focused on a task, is easily distracted and is excessively “on the go” in a manner that prevents him or her from performing well at school or in other settings. 
With the exact cause of ADHD still unknown, experts agree that family history of ADHD plays a role. Most cases are being diagnosed in children between the ages of four and six years. If left untreated, the majority of children living with this disorder will be at risk of developing low self-esteem, learning difficulties and even anti-social behaviour. 
According to recent findings, symptoms continue into adulthood for about a third of the children with ADHD. Research shows that many adults with ADHD have been living with the disorder since childhood, whether diagnosed or not. Often adults may be diagnosed with ADHD after their own child is referred for an evaluation. 
ADHD cannot simply be diagnosed by a blood test or physical assessment. Instead, a clinical diagnosis based on the patient’s history and the use of specially-designed diagnostic tools, will need to be conducted by specially trained healthcare professionals. 
The treatment of ADHD is multi-faceted and includes behaviour modification and medication, with treatments being tailored according to the needs of the individual. (Novartis, September 2009)
1. ADD ADHD Help Center, The History of ADHD and Attention Deficit Disorder, accessed on 24 August 2009. Available at http://www.add-adhd-help-center.com/newsletters/newsletter_15july03.htm
2. Ezine Articles, History of ADHD, accessed on 24 August 2009. Available at http://ezinearticles.com/?History-of-ADHD&id=217254
3. ADHD Q&A & Media Statement May 09
4. Health24, ADHD in the classroom, accessed on 24 August 2009. Available at http://www.health24.com/mind/ADHD/1284-3441,35672.asp
5. Ritalin – Attention Deficit Hyperactivity Disorder (Novartis document).
6. Men’s Health, Adults with ADHD are everywhere, accessed on 24 August 2009. Available at http://www.menshealthsa.com/print.php?art_id=3179