With a street price as low as 50p a hit, Ritalin is being sold as tablets and snorted, swallowed or smoked. Pupils are taking it for the buzz or, in rarer cases, as a study aid. But just how common is Ritalin misuse?
Paul Cooper, a professor of education at Leicester University, caused controversy last week by alleging parents were buying it to boost their children's performance during exam time. He has called it a "worrying development".
Although evidence of its use as a study aid in British schools is largely anecdotal, in the United States there is a growing body of research that suggests it has passed from being a recreational drug to a so-called "smart drug".
It is not the only one: 40 such compounds are in development, mostly aimed at psychiatric conditions such as Alzheimer's disease. But a handful, such as Modafinil, a stimulant used to treat narcolepsy, are gaining popularity among students as illicit study aids.
Specialists fear this could be the beginning of a "cognitive divide", creating a situation where wealthy pupils are able to pay for drugs to enhance their educational abilities, whereas poorer children are not.
Barbara Sahakian, a professor of neuropsychology at Cambridge University, says the increased use of drugs such as Ritalin already poses ethical dilemmas.
Will pupils feel pressured to take them? Will we drug-test children, like athletes, before exams? Will they increase equality or be affordable only by the rich?
Professor Sahakian says the idea may seem far-fetched but she believes that misuse is a sign children are already under too much pressure to achieve.
"The growing availability of these drugs and their relative lack of side effects means they are more appealing," she says. "But as expectations rise, they may have a coercive effect. Do we want a society where everyone is at the top of their game 247?"
Since they were first approved for prescription on the NHS in 2000, methylphenidates have been dogged by controversy - nine British children have died while taking them - and allegations that they are overprescribed, turning normally spirited children into "walking zombies". In healthy users, the drug can cause an amphetamine-like "rush". But side effects include sleeplessness, loss of appetite and increased blood pressure.
Although specialists agree it lets children with extreme attention deficit hyperactivity lead productive lives, a spokesman for Novartis, a manufacturer, said he "strongly advised" it should not be taken without prescription.
Research on Ritalin misuse in the UK is patchy, but a police investigation in County Durham and Northern Ireland in the early years of prescription found 30 pupils in a year group of 300 taking the drug illicitly.
Studies in the United States are more thorough. In 2004, the National Institute on Drug Abuse found 2.5 per cent of eighth graders (13- to 14-year-olds) and 5.1 per cent of 12th graders (17- to 18-year-olds) took the drug illegally, some for the "rush", others as a study aid, allowing them to work late and focus their minds.
"It is a problem and it has become more of an issue over the past year or so," said Sharon White, a professional officer for the School and Public Health Nurses Association, which reports that Ritalin dealing is increasingly common in British schools.
"We have heard of pupils selling their prescription medication or being targeted by bullies who steal it," she said.
With more than 300,000 prescriptions a year being written, some believe over-zealous treatment with Ritalin is already turning it into a form of cognitive-enhancer. Educational psychologist Allan Willis says he has seen it prescribed for healthy children whose hyperactive behaviour is nothing to do with chemical imbalances.
Like many Ritalin sceptics, Martha Farrah, a professor of psychology at Pennsylvania University, in the United States, believes some children are being treated as medical patients simply because they are not ideal pupils.
"One person's academic performance enhancement is another person's therapy," she said. "There is no objective laboratory test for ADHD, and undoubtedly some pretty normal kids are being given these stimulants because their parents want to enhance their school performance."
Ritalin is a brand of methylphenidate used to treat attention deficit hyperactivity disorder. Other popular brands include Concerta XL and Equasym.
More than 300,000 prescriptions a year are issued.
The drug is used to calm and focus hyperactive children. In healthy users, it can have amphetamine-like effects. A Cambridge University study indicated it can also improve the ability to deal with new tasks.
Side effects can include nervousness, insomnia, drowsiness or high blood pressure.
In the United States, about 2.5 per cent of 13- to 14-year-olds have illicitly taken the drug, according to a US study. There is evidence that Ritalin misuse - both as a recreational drug and as a study aid - has taken hold in the UK.