It goes by many names, K2, Spice, Bizarro, Scooby Snax, Kryp2nite and Stoopid, to name but a few, and it's setting off alarm bells across the United States.
Synthetic marijuana is being cited by police and public health officials for a dramatic surge in potentially lethal overdoses and drug-related offences nationwide.
Imported primarily from China, it's an inexpensive chameleon substance, its synthesised chemical ingredients forever being tweaked by underground labs keeping one step ahead of law enforcement.
"We're seeing it pop up all around the country," acting Drug Enforcement Administration (DEA) chief Chuck Rosenberg told NPR public radio this week.
"The dosage amounts vary. The chemicals vary. You and I could buy and use the same packet... and have vastly different reactions to it."
So far this year, poison control centres across the US have taken more than 5,200 calls specific to "fake weed."
That's more than the 3,680 calls they got in all of last year and the 2,668 calls handled in 2013, the American Association of Poison Control Centers says.
"Fake weed causes extreme anxiety, paranoia, panic attacks, alienation/disassociation, psychotic episodes and hallucinations," warns k2zombiedc.com, a city-run website aimed at Washington's youth.
"This behaviour has been labelled 'the zombie effect,'" it says.
Synthetic marijuana may look like pot to the naked eye, but its addictive and potentially lethal high derives from chemical compounds designed to mimic THC, the active ingredient in real marijuana.
Those chemicals are sprayed onto grass-like herbs that are then stuffed into condom-style packets featuring amateur-looking cartoonish graphics.
"Not for human consumption," some packages claim.
Compared to genuine pot, synthesised marijuana can be "up to 100 times as potent as THC" at stimulating brain receptors, said Marilyn Huestis, senior investigator at the National Institute on Drug Abuse.
It is sometimes sold under the counter at corner stores, gas stations and head shops, but it can easily be bought online with a credit card after a simple Google search.
"I love it," said a customer's glowing review of Bizarro on one website. "I'd give it a 9/10. Very potent product and shipping was really fast."
In a 2012 survey by the University of Michigan, synthetic marijuana was the second most consumed drug among US high school seniors after marijuana.
"It's a monstrous problem," Huestis told AFP.
Some versions of synthetic marijuana have been listed as a Schedule One drug on par with heroin, but the multitude of versions means they cannot all be deemed analogues of real pot and thus be found illegal.