The symptoms of attention deficit hyperactivity disorder (ADHD) can be categorised into 2 types of behavioural problems:

• inattentiveness (difficulty concentrating and focusing)
• hyperactivity and impulsiveness

Many people with ADHD have problems that fall into both these categories, but this is not always the case.

For example, around 2 to 3 in 10 people with the condition have problems with concentrating and focusing, but not with hyperactivity or impulsiveness.

This form of ADHD is also known as attention deficit disorder (ADD). ADD can sometimes go unnoticed because the symptoms may be less obvious.

ADHD is more often diagnosed in boys than girls. Girls are more likely to have symptoms of inattentiveness only, and are less likely to show disruptive behaviour that makes ADHD symptoms more obvious. This means girls who have ADHD may not always be diagnosed.

The symptoms of ADHD in children and teenagers are well defined, and they're usually noticeable before the age of 6. They occur in more than 1 situation, such as at home and at school.

Children may have symptoms of both inattentiveness and hyperactivity and impulsiveness, or they may have symptoms of just 1 of these types of behaviour.

Inattentiveness (difficulty concentrating and focusing)

The main signs of inattentiveness are:

• having a short attention span and being easily distracted
• making careless mistakes – for example, in schoolwork
• appearing forgetful or losing things
• being unable to stick to tasks that are tedious or time-consuming
• appearing to be unable to listen to or carry out instructions
• constantly changing activity or task
• having difficulty organising tasks

Hyperactivity and impulsiveness

The main signs of hyperactivity and impulsiveness are:

• being unable to sit still, especially in calm or quiet surroundings
• constantly fidgeting
• being unable to concentrate on tasks
• excessive physical movement
• excessive talking
• being unable to wait their turn
• acting without thinking
• interrupting conversations
• little or no sense of danger

These symptoms can cause significant problems in a child's life, such as underachievement at school, poor social interaction with other children and adults, and problems with discipline.

Although not always the case, some children may also have signs of other problems or conditions alongside ADHD, such as:

• anxiety disorder – which causes your child to worry and be nervous much of the time; it may also cause physical symptoms, such as a rapid heartbeat, sweating and dizziness
• oppositional defiant disorder (ODD) – this is defined by negative and disruptive behaviour, particularly towards authority figures, such as parents and teachers
• conduct disorder – this often involves a tendency towards highly antisocial behaviour, such as stealing, fighting, vandalism and harming people or animals
• depression
• sleep problems – finding it difficult to get to sleep at night, and having irregular sleeping patterns
• autistic spectrum disorder (ASD) – this affects social interaction, communication, interests and behaviour
• dyspraxia – a condition that affects physical co-ordination
• epilepsy – a condition that affects the brain and causes repeated fits or seizures
• Tourette's syndrome – a condition of the nervous system, characterised by a combination of involuntary noises and movements (tics)
• learning difficulties – such as dyslexia

In adults, the symptoms of ADHD are more difficult to define. This is largely due to a lack of research into adults with ADHD.

As ADHD is a developmental disorder, it's believed it cannot develop in adults without it first appearing during childhood. But symptoms of ADHD in children and teenagers often continue into adulthood.

The way in which inattentiveness, hyperactivity and impulsiveness affect adults can be very different from the way they affect children.

For example, hyperactivity tends to decrease in adults, while inattentiveness tends to remain as the pressures of adult life increase.

Adult symptoms of ADHD also tend to be far more subtle than childhood symptoms.

Some specialists have suggested the following as a list of symptoms associated with ADHD in adults:

• carelessness and lack of attention to detail
• continually starting new tasks before finishing old ones
• poor organisational skills
• inability to focus or prioritise
• continually losing or misplacing things
• forgetfulness
• restlessness and edginess
• difficulty keeping quiet, and speaking out of turn
• blurting out responses and often interrupting others
• mood swings, irritability and a quick temper
• inability to deal with stress
• extreme impatience
• taking risks in activities, often with little or no regard for personal safety or the safety of others – for example, driving dangerously

As with ADHD in children and teenagers, ADHD in adults can occur alongside several related problems or conditions.

One of the most common is depression. Other conditions that adults may have alongside ADHD include:

• personality disorders – conditions in which an individual differs significantly from the average person in terms of how they think, perceive, feel or relate to others
• bipolar disorder – a condition affecting your mood, which can swing from one extreme to another
• obsessive compulsive disorder (OCD) – a condition that causes obsessive thoughts and compulsive behaviour

The behavioural problems associated with ADHD can also cause problems such as difficulties with relationships and social interaction.