The health service is facing a growing bill from the record number of people being given drugs to combat attention-deficit hyperactivity disorder (ADHD), figures show.

In 2011, GPs wrote almost 715,000 prescriptions for drugs used to treat ADHD - a seven-fold increase on the number of prescriptions given in 1997.

The number of prescriptions for methylphenidate drugs, including Ritalin, have soared over the last 15 years, according to data from the Health and Social Care Information Centre.

In 1997, doctors wrote out 92,100 prescriptions for the stimulants. But the figure has steadily increased and now stands at 714,800.

The drug works by affecting certain chemicals in the brain which may help to reduce some of the symptoms of ADHD.

Common symptoms include a short attention span, restlessness or constant fidgeting or being easily distracted.

Symptoms tend to be first noticed at an early age. It is normally diagnosed between the ages of three to seven and is more common in boys.

It is estimated the condition affects 2 to 5 per cent of school-aged children and young people. However, it can be a life-long condition and many children continue to show symptoms as a teenager and adult.