An herb-and-chemical compound sold legally in the U.S. as incense is sending many of those who smoke it to the hospital, Reuters reported July 29.

The compound, known as K2, interacts with brain receptors in a way that is said to be similar to marijuana. Unlike marijuana, not much is known about the chemical makeup of the compound.

Officials said more and more people who smoke the “synthetic marijuana” have reported to emergency rooms and poison-control centers with symptoms ranging from anxiety, hypertension, and vomiting to severe paranoia and hallucinations.

U.S. poison-control centers received 13 calls related to K2 a year ago, while 766 cases have been reported in the first half of 2010, said Anthony Scalzo, medical director for the Missouri Poison Center.

The concern, according to Scalzo, is that the surge “may represent the tip of an iceberg.”

Editor's note, Aug. 30, 2010: Ten states — including Alabama, Louisiana, North Dakota, Tennessee and Kentucky — “have already passed some form of a [K2] ban, according to data from the National Conference of State Legislatures,” Reuters reported.