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

These categories are:

hyperactivity and impulsiveness
inattentiveness

Most people with ADHD have problems that fall into both these categories, but this isn’t always the case.

For example, some people with the condition may have problems with inattentiveness, 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.

Symptoms in children and teenagers

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

The main signs of each behavioural problem are detailed below.

Inattentiveness

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 at 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.

Related conditions in children and teenagers

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
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 called tics
learning difficulties – such as dyslexia

Symptoms in adults

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

ADHD is a developmental disorder; it’s believed that it can’t develop in adults without it first appearing during childhood. But it’s known that symptoms of ADHD often persist from childhood into a person’s teenage years, and then adulthood.

Any additional problems or conditions experienced by children with ADHD, such as depression or dyslexia, may also continue into adulthood.

By the age of 25, an estimated 15% of people diagnosed with ADHD as children still have a full range of symptoms, and 65% still have some symptoms that affect their daily lives.

The symptoms in children and teenagers, which are listed above, is sometimes also applied to adults with possible ADHD. But some specialists say that 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 get worse as the pressure of adult life increases. Adult symptoms of ADHD also tend to be far more subtle than childhood symptoms.

Some specialists have suggested the following 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

Additional problems in adults with ADHD

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

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

personality disorders – conditions in which an individual differs significantly from an average person, in terms of how they think, perceive, feel or relate to others
bipolar disorder – a condition that affects your moods, 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, social interaction, drugs and crime. Some adults with ADHD find it hard to find and stay in a job.