DENVER, Colo. --

It looks like marijuana and gives users a similar high, but unlike marijuana, a substance known as K2, Spice or Zohai, is legal in the United States and for sale in head shops all over Colorado.

Since January, the Rocky Mountain Poison Control Center (RMPC) has received 11 reports of Colorado teens landing in emergency rooms with alarming symptoms after smoking K2.

Dr. Alvin Bronstein, medical director of the RMPC, is leading federal research on K2. Bronstein said though K2 is considered a legal pot substitute, the symptoms appear more serious.

"People get agitated," said Bronstein. "They can become irritable, they can get confused. They can be tremulous. Their blood pressure goes up and their heart rate goes up."

K2 is sold in small packets, purportedly as incense. Bronstein said K2 is made up of herbs, mixed with a powerful synthetic chemical that mimics the effects of THC, the active ingredient in marijuana.

The packaging for K2 reads "not for human consumption," but when 7NEWS took a hidden camera into a Loveland head shop to buy K2, salespeople willingly counseled us on how to get high on it.

"Take one or two hits and then wait five minutes," one salesperson told us.

Bronstein said K2 has not been tested on humans and was never meant to be ingested.

"They're smoking so many different agents that were never designed to be taken into a person's lungs," said Bronstein. "Is this going to cause lung damage? I don't know. Is it going to cause damage to the brain long term? I don't know."

The substance was created in medical labs by Dr. John W. Huffman, a Clemson University researcher, as a way to study the effects of marijuana on lab animals. It has a different molecular structure than marijuana, but Bronstein said it was designed to stimulate the same receptors.

"These are like the poison that got out of the laboratory," said Bronstein.

By 2008, K2 was being used recreationally throughout Asia and Europe. It has only been in the past year, after at least a dozen European countries banned the substance, that K2 made its way to the United States.

Reporters with 7NEWS discovered dozens of YouTube videos showing young people getting high on K2.

Bronstein said nationwide, there have been 160 reports to poison control centers of K2 users being hospitalized with respiratory issues and increased blood pressure. The users are typically young men in their teens and early 20s.