A package of K2, a concoction of dried herbs sprayed with chemicals. Police in Calgary seized $30,000 of synthetic marijuana from several city retail outlets. ((Kelley McCall/Associated Press))

Police in Calgary say they have seized a synthetic form of marijuana for the first time after raids on seven retail stores across the city.

Officers executed search warrants on three outlets of Bongs and Such, three outlets of Smoker's Corner and a Grass Roots store, officials said.

They found $30,000 worth of the illegal product — a concoction of dried herbs sprayed with chemical — which mimic the effects of marijuana, police said.

A warehouse was also searched and found to be storing the drugs, which are classified in Canada under the Controlled Drug and Substances Act.

The products are sold under several brand names, including "Spice", "K-2", "Yucatan Fire", "Tribe" and "Skunk".

According to U.S. medical reports, users have suffered side effects including panic attacks, heart palpitations, hallucinations, delusions and vomiting, police said.

"I think when you actually take a look at the product itself, it actually says it's not for human consumption. It's one of the things placed on the product to, I guess, avoid liability," said Det. Collin Harris of the Calgary police drug unit.

Despite that, people working in the stores demonstrated to undercover officers how to prepare the drug and how to smoke it, Harris said. 

The intended clientele would be teenagers — who might believe the substance is legal — he said.

In November the U.S Drug Enforcement Agency began the process of making the substances illegal.

Police in Calgary first became aware of synthetic marijuana in October 2010, following a large seizure of the drug by the Canadian Border Services Agency.  

There have been as many as 50 seizures of the drug across Canada since 2008.