New figures from the Care Quality Commission (CQC) show prescriptions of the stimulant Ritalin went up by 56 per cent from 2007 to 2012.

The drug, chemical name methylphenidate, is the most popular treatment for attention deficit hyperactitivy disorder. Prescriptions by NHS doctors went up 11 per cent from 2011 to 2012, when the drug was dished out 657,358 times.

What’s driving the increase?

The most obvious answer is that more people are being diagnosed with ADHD and prescribed Ritalin, but the CQC also raises the possibility that the psychostimulant is being misused as a “smart drug”, perhaps by students who think it will help them concentrate.

The health watchdog specifically mentions this in relation to prescriptions by private doctors rather than the NHS, noting that private prescriptions of Ritalin went up 24 per cent last year.

The report says: “We are also aware of the possibility that methylphenidate could be diverted and abused, and for this reason we recommend that its use should be monitored carefully.

“We are aware of reports in the media and scientific literature that it is being abused as a smart drug to improve cognitive function.”

The report also points out that another stimulant, Dexamfetamine, is the second most commonly privately prescribed controlled drug.

The drug is also a common treatment for ADHD but like Ritalin, it can be abused as a stimulant. It’s not even in the top 10 controlled drugs prescribed by the NHS.

Does this reflect parents turning to private doctors to diagnose ADHD, or is there a suggestion that privately-prescribed drugs are more likely to get into the wrong hands? It’s difficult to say.

How many students are taking smart drugs?

There certainly are numerous reports about students guzzling Ritalin and other so-called “nootropics” like modafinil and piracetam to help them cram for exams, but as with most drug use, hard statistics are hard to come by.

Some surveys, usually of students in the US, appear to show that the use brain-enhancing drugs is becoming widespread in universities.

But this 2011 meta-analysis found that many questionnaires were flawed and the better ones tended to show about 3 to 6 per cent of students using stimulants to help them work.

A survey of German university students found that only 0.26 per cent reported using prescription drugs to improve mental performance.

So is ADHD on the rise?

Maybe. Again, we don’t have precise numbers about the prevalence of diagnosis of this condition.

NICE, which sets clinical guidelines for UK doctors, quotes a 2003 study of 10,000 schoolchildren, which found that 3.62 per cent of boys and 0.85 per cent of girls had ADHD. A 2007 review of prevalence rates in different countries came up with an international average of 5.3 per cent.

We know that diagnosis rates have risen in the UK, because ADHD was virtually unknown 30 years ago and the NHS now calls it “the most common behavioural disorder in the UK”, but it’s difficult to be precise.

The US Center for Disease Control and Prevention says 8.4 per cent of American children aged 3 to 17 have been diagnosed with the disorder.

ADHD affects a smaller percentage of adults – perhaps 3-4 per cent, according to research quoted by NICE, but it is being increasingly recognised by psychiatrists in the US.

What causes it?

No-one knows. In fact, there is no established physical test you can do to prove a child has ADHD. It doesn’t show up on a brain scan or in a blood sample, although there is some evidence that genetic factors and lifestyle choices like smoking during pregnancy are linked to a higher risk.

The most common diagnostic tool is the behavioural checklist put forward by the American Psychiatric Association.

Children have to have at least six out of nine symptoms. These include things pretty common to most children like “does not seem to listen when spoken to directly” and “fails to finish schoolwork, chores or workplace duties”.

But you have to have at least six out of nine symptoms “persisting for at least 6 months to a degree that is maladaptive and inconsistent with developmental level”.

NICE says psychiatrists should not rely solely on checklists like this, and the symptoms have to surface in two or more settings like home and school.

Despite guidelines like this, some researchers say ADHD is easy to misdiagnose. A US study from 2010 claimed that the youngest children in pre-school classes are much more likely to be diagnosed than older children in the same group.

The implication was that immature behaviour was being mistaken for a medical disorder, with the possible result that nearly 1 million children in the US have been wrongly diagnosed.

Is Ritalin the only drug being prescribed more often?

Far from it. In a long-term study in the British Journal of Psychiatry last year, Stephen Ilyas and Joanna Moncrieff found rising trends in prescriptions for most psychiatric drugs.

Antidepressants like Prozac, mood stabilisers and antipsychotic drugs designed to treat illnesses like schizophrenia all rose year-on-year from the late 1990s.

Population growth doesn’t explain the trend. Antidepressants in particular shot up by 10 per cent a year on average from 1998 to 2010.

Clearly, there are a number of explanations for all this pill-popping. Perhaps rates of mental illness are going up – the pressures of modern life and all that. But the authors thought that was unlikely.

They found no evidence of increased diagnosis of depression, and instead cited research indicating that more than 40 per cent of antidepressants are being prescribed to people who aren’t really depressed.

There was also evidence that powerful antipsychotic drugs are being prescribed to people who are not diagnosed with psychosis but suffering from minor conditions like insomnia.

So Ritalin is just one of many drugs being prescribed in ever greater numbers, and there are questions about drugs being overprescribed for conditions they were not intended to treat.

By Patrick Worrall