Although symptoms of ADHD - Attention Deficit Hyperactivity Disorder – have been noted by physicians for centuries, it was only in the late 1960s and 1970s that hyperactivity and attention deficit as a result of brain function began to be studied and defined.

It is now well-established that untreated ADHD can cause significant mental health problems, educational and occupational issues and unnecessary distress & loneliness.

[Read more: What is Lupus? Everything you need to know]

[Read more: What might be causing your long-term cough?]

But what exactly is ADHD, how is it diagnosed, and how can it be managed and treated?

What exactly is ADHD?

ADHD is a mental disorder characterised by a group of behavioural symptoms that usually fall into the categories of inattentiveness, and hyperactivity and impulsiveness. Most people who are diagnosed with ADHD have symptoms that fit into both these groups.

Symptoms of ADHD tend to be noticed at an early age - most cases are diagnosed when children are 6 to 12 years old.  ADHD is a developmental disorder; it's believed that it can't develop in adults without it first appearing during childhood.

The exact cause is unknown, but genetics are a considered a factor – the child of a parent who has or had ADHD is more likely to be diagnosed with the condition. Other factors can include being born prematurely, having a low birth weight, and smoking, alcohol or drug abuse during pregnancy, as well as certain infections.

What are the symptoms of ADHD?

Inattentiveness symptoms can include being easily distracted, making simple mistakes in schoolwork, being forgetful, not listening or taking in simple instructions, not being able to stick to tasks or constantly changing tasks or activities.

[Read more: Bowel cancer - the 5 warning signs you shouldn't ignore]

Hyperactivity and impulsiveness symptoms may include being unable to sit still even in calm or quiet situations, excessive movement or talking, interrupting conversations, not being able to wait their turn, or acting without regard to danger.

The symptoms of ADHD usually improve with age, but many adults who are diagnosed with the condition at a young age continue to experience problems.

My child can be inattentive and fidget. Does this mean they have ADHD?

Many children go through phases where they're restless or inattentive. This is completely normal and doesn't necessarily mean they have ADHD – but if you have concerns about your children it might be worth talking with their teacher.

To be diagnosed with ADHD, your child must have been displaying symptoms since before the age of 12, and continuously for at least six months; symptoms must have been evident in at least two different settings – for example, at home and at school – and making their lives considerably more difficult on a social, academic or occupational level

[Read more: Vascular dementia - what is it, and what are the risk factors?]

It also needs to be clear that the symptoms aren't just part of a developmental disorder or difficult phase, or better accounted for by another condition.

You can speak to your GP if you’re still worried about your kids – it’s also a good idea to do so if you're an adult and you think you may have ADHD, but weren't diagnosed with the condition as a child.

How is ADHD treated?

There is no specific cure for ADHD, but children can be treated with counselling, educational support, and medication if appropriate – or a combination of the three.

Therapies used include cognitive behavioural therapy, family therapy, interpersonal psychotherapy, social skills training. Medication is often the first treatment offered to adults with ADHD, although psychological therapies may also help.