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Synthetic cannabinoids are sometimes called synthetic pot, fake weed, or by the brand names Spice and K2. The products are illegal, but may be sold in gas stations, convenience stores, and on the internet, and could be labeled "not for human consumption."

Of the 70 cases in the Chicago area and in Central Illinois, two people have died and at least nine have tested positive for exposure to brodifacoum, which is a blood-thinning drug used as a rat poison. All have been hospitalized because they had uncontrollable bleeding, including coughing up blood, blood in the urine, severe bloody noses, or bleeding gums.

Brodifacoum is a powerful anticoagulant, said Alfred Aleguas Jr., the managing director of the Florida Poison Information Center in Tampa, Florida. It's similar in action to the blood-thinning drug warfarin, which is used medically to treat people at high risk for blood clots. However, warfarin is used carefully and monitored to prevent abnormal bleeding in patients, he said.

“Brodifacoum is what they call 'super warfarin,'" he told BuzzFeed News. It's used as a rat poison and is better known to poison control centers as a source of self-inflicted poisoning.

"This is the first time we’ve ever seen it used as a contaminant in a drug of abuse," Aleguas said.

However, synthetic cannabinoids can be dangerous and deadly on their own, even when not contaminated with a poison. While synthetic cannabinoids may look like marijuana, they are in fact artificial chemicals that are sprayed on plant material, which is then smoked to get high or sold as a liquid, vaporized, and inhaled in an e-cigarette.