Teen use of over-the-counter cold and cough medicines to get a cheap high – a practice known as “robotripping” – is rising 50 percent a year and becoming one of the fastest-growing drug abuse problems in the U.S., according to a study released this week.

Since 1999, teen abuse of Coricidin pills, Robitussin syrup and other common medications has risen tenfold, data from the California Poison Control System show. The widely available and inexpensive medicines are growing in popularity while use of illegal drugs such as Ecstasy, LSD and the date rape drug GHB have dropped, according to the report.

“Hey, Mom and Dad, pay attention,” said Marilyn MacDougall, executive director of the Orange County Sheriff Department’s drug abuse prevention program. “Over-the-counter medicines are the upcoming way your kids are going to abuse drugs.”

The cold remedies are valued for dextromethorphan, which can cause hallucinations, out-of-body experiences and, in extreme cases, death. The drug, known by kids as DXM or Dex, was first abused in the 1960s when it was in a cough medicine called Romilar, which was withdrawn from the market in 1973.

Health officials spotted a revival in the late 1990s. About two-thirds of abusers now take Coricidin HBP Cold & Cough, whose candy-red tablets are nicknamed CCC, Triple C and skittles. Robotripping takes its name from Robitussin, the second-most-popular drug.

A study in May by the Partnership for a Drug-Free America estimated that 2.4 million teens – about 1 in 10 – got high on cough medicines in 2005. That puts it on par with cocaine and slightly above methamphetamines.

School administrators are learning of the craze the hard way. In El Dorado, a community of apple orchards and Christmas tree farms outside of Sacramento, Calif., seven high school students were rushed to the emergency room in October after taking Coricidin. The Union Mine High School students had purchased several boxes at a dollar store and swallowed five to eight tablets each during their morning snack time.

Administrators learned of it after one student started vomiting in class.

“This is new to us – it caught a lot of people by surprise,” Principal Carl Fickle said. “It didn’t catch the kids by surprise.”

The latest study, published Monday in the December issue of the Archives of Pediatrics and Adolescent Medicine, found that the growth of dextromethorphan abuse is being driven by children ages 9 to 17.

Abuse is most common among 15- and 16-year-olds, the study found. The number of 12- and 13-year-olds using the drug exceeds the number of 18-year-olds, indicating that it is popular in middle schools as well as high schools, according to senior author Ilene B. Anderson, a toxicology management specialist at the California Poison Control System in San Francisco.

“I did not expect 12-year-olds to be abusing it,” Anderson said.

The study was based on a review of 1,382 calls made to the California Poison Control Center over a six-year period involving cases of dextromethorphan exposure. Those calls were generally made in emergency situations, usually by physicians treating overdose patients in hospitals. They represent only a fraction of overall drug use, Anderson said.

“If someone is abusing dextro and gets a high, they don’t call us,” she said. “I think it is grossly underreported.”

The researchers compared the California findings with general statistics from the American Association of Poison Control Centers and the Drug Abuse Warning Network and found that the trends here are in line with the rest of the country.

Dextromethorphan appeals to teens because it “is easily and legally available in most pharmacies and large grocery stores,” Anderson said. “It’s relatively inexpensive – in many cases, one package can cause hallucinations.”

Web sites offer testimonials about the buzz the drug provides. Some users describe it as “slightly intoxicating” while others compare their experiences to the hallucinatory effects of ketamine or PCP.

Dextromethorphan users can consult online calculators – where they enter their weight, brand of medicine and “plateau” of high they want to achieve – to determine how big a dose to take.

And because the cough remedies look innocuous, Anderson said, “you can have a package, and your parents would never even suspect it, compared to a little white bag of powder which certainly would cause a red flag to go up.”

When taken in large quantities, dextromethorphan can make the heart race and blood pressure rise. Some users become agitated while others become lethargic, confused, dizzy or act as if they are inebriated. Life-threatening side effects include seizures and elevated body temperature, Anderson said.