The ban, proposed in November 2010 amid increasing reports of seizures, hallucinations and dependency linked to the fake pot, was "necessary to prevent an imminent threat to public health and safety," according to the Drug Enforcement Administration. It has now banned K2 and five chemicals used to make it.
K2 was sold openly in head shops and online as incense. It largely avoided regulation in the United States because it was sold in packages that stated it was not for human consumption.
Little is known about the long-term effects of the fake pot, also known as Spice, Demon, Genie, Zohai and a host of other names. But its short-term effects, which include soaring heart rates and paranoia, have landed some of those who smoked it in the hospital.
"This emergency action was necessary to prevent an imminent threat to public health and safety," said the Drug Enforcement Agency in a statement. The ban, it said, "will remain in effect for at least one year while the DEA and the United States Department of Health and Human Services (DHHS) further study whether these chemicals should be permanently controlled."
Dr. Anthony Scalzo, a professor of emergency medicine at St. Louis University and the medical director of the Missouri Poison Control Center, first reported a spike in K2 cases in early 2010 and immediately started studying the effects of the substance.
"The common thread throughout all the cases is this degree of anxiety, agitation, fast heart rate and elevated blood pressure," Scalzo said.
Some people reported hallucinations and near-death experiences, but Scalzo said, "The hallucinations are not always consistent and I suspect it's perhaps a dose effect. Maybe some individuals are using more."
In some instances, the drug has been linked to suicide.
"Smoking something that's supposed to be substitute for marijuana, you're expecting to be mellow," Scalzo said. "Unfortunately, you're not getting that. No one really sort of field tested these chemicals. We don't even know where exactly this stuff is made."
K2 was first developed by an undergraduate student in the lab of Clemson University chemist John Huffman. Its active ingredients are synthetic cannabinoids, chemicals that imitate the effects of tetrahydrocannabinol (THC), the active ingredient in marijuana.
Huffman said the chemicals were designed as "research tools" and never intended for human consumption.
Three of the five banned chemicals -- JWH-018, JWH-073, JWH-200 -- bear Huffman's initials in their names. The other two are CP-47,497, and cannabicyclohexanol.
"Some of the compounds that are turning up in K2 and Spice samples are very sophisticated," Huffman said. "They are in fact not known cannabinoids. They are unique and very well designed and require considerable chemical expertise."
Increasingly, pure forms of the chemicals are being mixed with other herbs and compounds and then marketed as K2.
"Anybody that tries it is like playing Russian roulette," Huffman said. "You don't know what you're getting. It's just insane. Anybody who uses it is out of their tree."