Nearly 15 per cent of teenagers who are prescribed Ritalin or other stimulants have given away at least some of their pills, a new survey reports.

And more than seven per cent have sold their pills.

For the study, appearing in this week's Canadian Medical Association Journal, 13,549 randomly selected students in Atlantic Canada in grades 7, 8, 9, 10 and 12 were surveyed in 1998.

More than 700 of them were taking prescription stimulants such as Ritalin, dexedrine and benzedrine. And more than 1,100 of them said they had taken such stimulants for non-medical reasons that year.

The anonymous survey had a 99 per cent response rate among students who were in class.

Ritalin and other stimulants actually have a calming effect on people who need the drug, such as teens with attention deficit and hyperactivity disorder (ADHD).

But when most people take these drugs, they speed up the brain, producing a high.

Ritalin abuse is a growing problem, says Heather Dickson, who runs a drug counselling program in Halifax.

"We see them sharing, selling, trading," says Dickson.

"We see them crushing and snorting, trading it for other things, saving up their Ritalin for Friday night."

Stimulant abuse can be dangerous, especially when combined with alcohol or marijuana.

The author of the study, Christiane Poulin of Dalhousie University in Halifax, says keeping a closer eye on teens' pills is necessary.

"Physicians and parents should keep track of stimulant medication, especially when several months' supply is prescribed," she wrote.