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Deaths from synthetic marijuana have tripled over the past year, as have calls about poisonings and other adverse events, the Centers for Disease Control and Prevention reported Thursday.

The drugs are sold under names such as "spice," "K2," "black mamba" and "crazy clown," but they are all synthetic versions of cannabinoids, the active ingredient in marijuana. Although buyers may think they are more natural or legal than marijuana, they are illegal in all states and they are more dangerous.

“Between January and May 2015, U.S. poison centers in 48 states reported receiving 3,572 calls related to synthetic cannabinoid use, a 229 percent increase from the 1,085 calls received during the same January through May period in 2014,” Royal Law and colleagues at the CDC report.

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“The 2015 figures included a spike of 1,501 calls in April and 15 reported deaths, a three-fold increase over the five deaths reported in 2014,” they add in their report, published in the CDC’s weekly rundown of death and disease.

The Drug Enforcement Administration has been cracking down on synthetic cannabinoids, and some states, including Louisiana, have specifically outlawed them.

They are made using psychoactive chemicals sprayed onto plant material. It’s cut up for use like marijuana. Most people — 80 percent — smoke it, but it can be eaten. Adverse effects can include agitation, rapid heart rate, drowsiness, vomiting, and confusion.

“The increasing number of synthetic cannabinoid variants available, higher toxicity of new variants, and the potentially increased use as indicated by calls to poison centers might suggest that synthetic cannabinoids pose an emerging public health threat,” Law’s team reported.

In February, the Drug Enforcement Administration registered four newer synthetic cannabinoids as Schedule I drugs, meaning those caught manufacturing, handling or distributing them could face serious jail time.

They first began appearing in the United States in 2009, the American Association of Poison Control Centers says.

They’re different from synthetic speed products called “flakka”. But both are a growing problem.