GRAND RAPIDS -- At a shop called Orange on Holland's north side, clerks more than a week ago stopped selling an herb-based mixture police call synthetic marijuana.

They knew a new law banning the once-legal substance, sold under the brand name K2 and other names, was about to take effect.

"When we ran out of it, we didn't make any new orders," said a clerk at Orange, who did not want to be named.

Orange sold the product, under the brand name XXX, only to customers older than 18. But it was a voluntary measure, given there were no age restrictions on buyers.

Today, products termed synthetic cannabinoids are illegal after Gov. Jennifer Granholm signed a bill into law Thursday.

K2 and other products that go by "Spice" and "Mr. Smiley," are dried herbs sprayed with a chemical compound that, when smoked, creates a high similar to marijuana.

Manufacturers often market them as incense.

Medical experts say the substance, mostly made in China and South Korea, often causes a dramatic increase in heart rate and symptoms similar to having a schizophrenic episode. While the substance is largely untested, some lab tests link the chemicals to paralysis, according to a state House report on the bill signed Thursday.

The new law establishes a 90-day misdemeanor for anyone who uses or possesses the synthetic cannabinoids.

In the Grand Rapids and Holland areas, the substance was being sold at a handful of locations.

Kentwood Police Chief Richard Mattice said his officers have not had any trouble so far with synthetic marijuana users, but supports the law to make the substance illegal.

"If it's harmful in any way or emulates a harmful product, then it really isn't a legitimate product," he said.

The clerk at Orange said he did not disagree with banning the substance, although the only customer complaints about the herb mix came from a couple of angry parents upset their children had purchased it.

He said the store owner only sold the mix to compete with other stores selling similar products.

E-mail John Tunison: jtunison@grpress.com