Two men have died in Australia from what authorities say they suspect is a case of poisoning caused by a batch of synthetic cannabis.

The two men in Mackay in central Queensland, one age 33 and the other 41, died on successive days, say police who've initiated a probe into recent incidents and a spate of hospitalizations linked to the synthetic cannabis.

Medical experts sounded an alarm over the usage of the substances.

"People need to be cautious about consuming these products where the ingredients are unknown," said Dr. David Farlow of the Mackay Hospital, where the 41-year-old man died after being on life-support.

"These drugs pose a major risk to an individual's physical and mental health and the community," he said.

Drug users are increasingly turning to the synthetic products claimed to provide the same affect as natural marijuana by mimicking THC, the active ingredient contained in the natural version.

The products are marketed under a variety of names, with one of the most common being sold as "Spice."

Originally created to study the neurobiology of cannabis in animal testing, the synthetic compounds were never intended for human use.

"Synthetic cannabinoids certainly have the potential to be significantly more dangerous than the natural plant material that they supposedly mimic," says David Caldicott, an emergency physician with the Australian National University in Canberra.

The problem, the experts say, is that such compounds are fairly easy to synthesize, which has created a global cottage industry making and selling synthetic cannabis without regulation, standards or quality control.

The result is "a large variety of synthetic cannabinoids with largely unknown toxicity," says Richard Kevin, a psychopharmacology doctoral candidate at the University of Sydney.

And "because they are simply sprayed onto whatever carrier plant material is chosen," Caldicott points out, "hot spots can occur where the concentration is higher than intended."

Many drug users have turned to synthetic varieties in an effort to frustrate drug testing, experts say, since although the effects are similar to marijuana the molecular makeup of most synthetic versions is different and they are not picked up by standard drug testing.

Although some synthetic cannabinoids appear to be relatively safe, Kevin says, others have been linked to panic attacks, acute kidney injury and seizures.

In addition, he says, his own studies using mice suggest "long-term memory impairment after heavy chronic dosing."

Australian states have outlawed synthetic drugs that mimic cannabis, but to keep ahead of the law and drug tests, many makers constantly alter their recipes.

"The rate of evolution of these drugs is such that many have never been seen before," Caldicott says.

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