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By Nick Wasson, M.D.:

Spice. K2. Herbal incense.

You've heard the names, and now these drugs known as synthetic marijuana have been implicated in acute kidney damage.

A new report from the U.S. Centers for Disease Control and Prevention links the so-called designer drugs to 16 cases of unexplained kidney failure.

"We knew that spice was dangerous. It's not a safe alternative to marijuana," said report author Dr. Michael D. Schwartz of the National Center for Environmental Health's Office of Environmental Health Emergencies. "As newer compounds come out in spice products, there is the risk of unpredictable toxicities."

There was a similar pattern of symptoms in the 16 cases: all but one had nausea vomiting, and 12 patients reported abdominal, back, and possible flank pain. The patients ranged in age from 15 to 33, all but one were male, and all had healthy kidneys prior to their complaints.

All patients were hospitalized, and five needed dialysis treatments. All of them showed signs of recovery in three days.

"It's unusual for young people to have unexplained kidney failure," said Dr. Gregory Collins, head of the Cleveland Clinic's Alcohol and Drug Recovery Center. "We haven't seen that before with these substances, but this wouldn't surprise me. These are dangerous compounds that are made often in China and imported into the U.S.

"You wouldn't know what you're getting," he added. "You'll find that these laboratories are putting out in the China market over 100 different compounds. People can order these over the internet and get a shipment. It's shocking how it's legal."

Some progress has been made, however. Congress last summer passed a law putting 26 synthetic drugs under the list of controlled substances, including 15 types of synthetic marijuana compounds.

Several types were implicated in the cases linked to kidney failure, including "Spice Gold," "Mad Monkey," "Phantom Wicked Dreams," "Mr. Happy," "Clown Loyal," "Lava," and "Flame 2.0."

In seven cases, lab tests were performed on either the product or through blood and urine tests, and a new synthetic marijuana compound termed "XLR-11? was found in several specimens.

Collins urged people to "stay away" from the dangerous products, adding that parents should "be very vigilant."

"Kids talk about this stuff, they blog about it," he said. "Parents need to be very vigilant about kids purchasing these types of products, and step in and take action."