Teenagers who have been prescribed sleep or anti-anxiety medications are more prone to eventually abusing those drugs than other teenagers are, a study suggests.

There is a 12-fold increase in the likelihood of abuse among those who have been on the drugs under a doctor's prescription, researchers say.

The findings come as the number of prescriptions of such drugs for teens has increased dramatically in the last 10 years.

"Prescribers and parents don't realize the abuse potential," says lead researcher Professor Carol J. Boyd at the University of Michigan School of Nursing. "These drugs produce highly attractive sensations, and adolescents may start seeking the drugs after their prescriptions run out."

The findings strongly suggest teenagers should undergo substance abuse assessments before being prescribed anti-anxiety or sleep medications, she says.

Almost nine percent of more than 2,700 middle and high school students from the Detroit area surveyed in Boyd's study had, at one time or another, been prescribed an anti-anxiety medication such as Valium, Xanax or Klonopin, or sleep medications such as Ambien, Restoril or Lunesta.

All of those medications have been found to be potentially addictive in some circumstances, the researchers noted.

Of the students in the study, those most likely to abuse some form of anti-anxiety or sleep drug were white, female or had used the drug under a valid doctor's prescription for a number of years, the researchers found.

Abusing the drugs can lead to overdoses, substance abuse problems or even criminal activity during attempts to obtain the drugs illegally, they said.

Teens often turn to family members or school friends to obtain the drugs when their prescriptions run out, Boyd notes.

"The public often thinks that nonmedical use of these prescription drugs is driven by doctor shopping and drug dealers, but it isn't," she says. "It is driven by people with prescriptions who divert their pills to other people, who are usually friends or family members."

In additional to substance abuse assessments, the researchers urge strict limits on prescription refills and suggest pre-prescription education courses to inform teens and parents of the risks of abusing these medications.

"This is a wake-up call to the medical community as far as the risks involved in prescribing these medications to young people," Boyd says. "When taken as prescribed, these drugs are effective and not dangerous. The problem is when adolescents use too many of them or mix them with other substances, especially alcohol."