For the second weekend in a row, overdoses on synthetic marijuana sent multiple teens to the hospital, reported The San Diego Union Tribune. This past Saturday, paramedics treated 16 people who fell ill after using the drug commonly referred to as “Spice,” while last Sunday, eight people, including one 13-year-old, required medical attention.

Spice is the second-most popular illegal drug used by high school seniors (marijuana is the first), according to the National Institute of Drug Abuse (NIDA). The drug is a mix of herbs and manmade chemicals that cause mind-altering effects, NIDA explains. Usually called “fake weed” on the street, Spice is a cannabinoid and so related to the chemicals found in the marijuana plant. However, the artificial version is frequently much stronger and more unpredictable than natural marijuana.

Police are now investigating where the drug came from, reported the Tribune.

More Men than Women

Spokesman Lee Swanson said the San Diego Fire-Rescue Department received more than 10 calls involving 16 people between 10 a.m. and 6:30 p.m. on Saturday. Most of the calls involved patients in their late teens and early 20s, with 11 requiring hospitalization, and three found in serious condition, said Swanson. Symptoms included mild nausea, agitation, rapid heartbeat, difficulty breathing, and unconsciousness.

In 2011, Spice was mentioned 28,531 times in emergency room visits, NIDA reports, a sharp spike compared to 11,406 references during 2010. On the opposite coast, public health officials reported in September more than 4,500 synthetic cannabinoid-related emergency department visits in New York City alone. Men make up the overwhelming majority of ER visits: roughly 80 percent. Some heavy users experience withdrawal and addiction symptoms, and in a few cases, the synthetic drug has been linked with heart attacks and also death.

Precisely, the drug killed 15 people in the first half of this year, according to the Centers for Disease Control and Prevention.

Among the possible reasons Spice has become so quickly popular is easy access, plus a common misperception that it is “natural” and therefore harmless, suggests NIDA. Plus, some chemicals used in these herbal products cannot be detected by standard drug tests. Because specific chemical formulations have been outlawed, manufacturers simply change their particular formula as a way to sidestep the law. It is classified in a group of drugs referred to as "new psychoactive substances."

Most people smoke Spice by rolling a joint with cigarette papers, but some users make an herbal tea and drink it, according to NIDA. These herbal incense products are usually sold in colorful foil packages under a variety of brands. In the past, the most popular were K2 and Spice, yet today manufacturers package the product using, among many other names, Geeked up, Smacked, Scooby Snax, Green Giant, Red Giant, Mr. Bad Guy, Joker, Black Mamba, Kush, and Kronic.