Many children go through phases where they're restless or inattentive. This is often completely normal and does not necessarily mean they have ADHD.
However, you should consider raising your concerns with your child's teacher, their school's special educational needs co-ordinator (SENCO) or GP if you think their behaviour may be different from most children their age.
It's also a good idea to speak to your GP if you're an adult and you think you may have ADHD but weren't diagnosed with the condition as a child.
Read more about diagnosing ADHD.
The exact cause of ADHD is unknown, but the condition has been shown to run in families. Research has also identified a number of possible differences in the brains of people with ADHD when compared with those without the condition.
Other factors suggested as potentially having a role in ADHD include:
ADHD can occur in people of any intellectual ability, although it's more common in people with learning difficulties.
Read more about the causes of ADHD.
Although there's no cure for ADHD, it can be managed with appropriate educational support, advice and support for parents and affected children, alongside medication, if necessary.
Medication is often the first treatment offered to adults with ADHD, although psychological therapies such as cognitive behavioural therapy (CBT) may also help.
Read more about treating ADHD.
Looking after a child with ADHD can be challenging, but it's important to remember that they cannot help their behaviour.
Some issues that may arise in day-to-day life include:
Adults with ADHD may also find they have similar problems, and some may have issues with relationships or social interaction.
Read about living with ADHD for information on coping with these issues.