Synthetic drugs once touted as legal alternatives to marijuana have gained a foothold among teenagers, with one in nine high school seniors surveyed last spring saying they had used so-called synthetic pot in the previous year.
The study, released Wednesday by the National Institutes of Health, is believed to be the first government attempt to survey the popularity of synthetic substances often marketed as "herbal incense" and sold under brands such as "Spice" and "K2."
"We actually were very surprised that the numbers were so high," said Dr. Nora Volkow, director of the National Institute on Drug Abuse, which sponsors the annual "Monitoring the Future" survey.
Volkow said the numbers suggest either the drug's use went undetected by officials for a while, or its rate of acceptance is rising rapidly. She said the data indicates the government must be "proactive" in dealing with the problem.
Senior students with the highest rate of use -- 13.5 percent -- were from the Midwest.
"Perhaps the rates are higher in the Midwest because people don't want to be lawbreakers, they think that it is legal and therefore they aren't doing anything wrong," said Carol Falkowski, drug abuse strategy officer for the Minnesota Department of Human Services. "There are numerous websites that still portray these products and say they're 100 percent legal."
The survey, based on responses from 47,000 students in grades 8, 10 and 12, showed that alcohol and cigarette use are at an all-time low since the survey began 37 years ago.
Fake pot was the second-most frequently used illegal drug behind natural marijuana, which 36.4 percent of seniors reported using in the same time period, according to the study. Frequent use of marijuana reached a 30-year peak among high school seniors. More than 90 percent of synthetic pot users surveyed said they had also used natural marijuana.