The deaths of two men—one yesterday and one today—and a rash of recent hospitalizations in Australia, all suspected to result from the use of synthetic cannabis, are focusing attention on a growing worldwide problem.

Drug users have been embracing products touted as producing a natural marijuanalike high. The effect is produced by synthetic compounds designed to mimic THC, the active ingredient in marijuana, which are sprayed onto plant material then often marketed as "Spice." However, "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 medical doctor at the Australian National University in Canberra.

The compounds were originally designed to study the neurobiology of cannabis in animals. They were never intended for human use. But "these drugs aren't too difficult to synthesize," says Richard Kevin, a psychopharmacology Ph.D. candidate at the University of Sydney in Australia who is studying the effects of the synthetic compounds on mice. He says a competent chemistry grad student could cook them up in a university lab. So a worldwide cottage industry has sprung up producing synthetic cannabis. But with no standards, no regulation, and no quality control, there is "a large variety of synthetic cannabinoids with largely unknown toxicity," Kevin says. And "because they are simply sprayed onto whatever carrier plant material is chosen,” Caldicott says, “hot spots can occur where the concentration is higher than intended."

Haphazard production has led to particularly toxic batches and clusters of poisoning. According to news reports, synthetic cannabis use killed 25 and sickened more than 700 in northern Russia alone last fall.

Kevin says one reason people use these products is to foil drug testing. Although the synthetic cannabis targets the same brain regions as THC, the molecular structures are different and escape detection by standard drug tests. Australian states have outlawed drugs that mimic cannabis. But proving cannabislike effects of any particular compound "can be tricky," Kevin says. And to keep ahead of the law and drug testing, makers are constantly tweaking their recipes. "The rate of evolution of these drugs is such that many have never been seen before," Caldicott says.

When buying synthetic cannabis, "you can’t know exactly what you’re getting, so you’re taking a big risk," Kevin says. He says that although some synthetic cannabinoids appear to be relatively well tolerated, others have been linked to acute kidney injury, panic attacks, and seizures. His own studies with mice suggest "long-term memory impairment after heavy chronic dosing."

"We need wittier and wiser responses to the problem of harm from drugs if these deaths are not to become a more frequent occurrence,” Caldicott says.