K2 is banned in some countries, including Sweden, Switzerland, South Korea, Chile, Germany and France, according to the U.S. Naval Criminal Investigative Service.
In the United States, the governors of Alabama, Georgia, Kansas, Kentucky and Tennessee have signed bills outlawing K2, although not all the laws have gone into effect yet. The Missouri legislature also passed a ban that will take effect unless the governor vetoes it before July 14.
Illinois, Louisiana, Michigan, New Jersey and New York are considering bills outlawing K2, according to USA Today.
The result for some is a mellow, marijuana-like high when smoked. But for others, the effects include anxiety, panic attacks, agitation, hallucinations and seizures, according to the Iowa Statewide Poison Control Center.
Research on how K2 and similar products affect the human body is still incomplete. While K2 has been available in Europe for a couple years, it wasn't until recently that it started showing up on U.S. officials' radars.
Linda Kalin, director of the Iowa Statewide Poison Control Center, first heard about K2 through the poison control's information exchange site in February. The warning came from Missouri, where multiple doctors were reporting patients sick from it.
"At that point, we learned as much as we could," Kalin said.
In March, the Iowa center received its own call from a hospital where a teenager was complaining of agitation, twitching and an increased heart rate.