Despite being the most commonly studied and diagnosed psychiatric disorder in children and adolescents, the cause in the majority of cases is unknown.
ADHD is diagnosed approximately three times more in boys than in girls.
The United States uses ADHD diagnoses criteria different from the diagnoses criteria used in Europe. The United States diagnoses ADHD 3-4 times more often with this criteria.
The Drug Enforcement Agency has classified ADHD drugs Ritalin, Adderall and Dexedrine as Schedule II Stimulants. This is the same drug classification as Cocaine.
Sales of stimulant medication for ADHD in 2012 reached nearly $9 billion, more than five times the $1.7 billion a decade earlier.
The number of children on medication for ADHD had soared from 600,000 in 1990 to 3.5 million in 2012.
There has been a 42% increase in the number of reported cases of ADHD since 2003.
In 2010 there were 31,244 Emergency Room visits related to persons taking ADHD medications, most of the cases were a result of overdose or acute side effects which can include mania and hallucinations.
Based on the presenting symptom ADHD can be divided into three subtypes: predominantly inattentive, predominantly hyperactive-impulsive, and combined type.
As ADHD is common, natural selection likely favored these traits, at least individually, and they may have provided a survival advantage.
Children exposed to lead, even low levels, or may develop problems which resemble ADHD and fulfill the diagnosis.
There are children who may react negatively to synthetic food dyes or preservatives.
The diagnosis of ADHD can represent family dysfunction or a poor educational system rather than an individual problem.