Spice products are popular among young people; of the illicit drugs most used by high-school seniors, they are second only to marijuana. (They are more popular among boys than girls — in 2012, nearly twice as many male 12th graders reported past-year use of synthetic marijuana as females in the same age group.) Easy access and the misperception that Spice products are “natural” and therefore harmless have likely contributed to their popularity. Another selling point is that the chemicals used in Spice are not easily detected in standard drug tests.

http://www.drugabuse.gov/publications/drugfacts/k2spice-synthetic-marijuana