Illinois public health officials are sounding the alarm about synthetic marijuana that is being distributed in the Chicago area and the central part of the state. Users have been hospitalized with severe bleeding, and now fatalities are being reported.

Synthetic cannabinoids, also known as K2 or Spice, has been linked to 56 cases in which people in the state experienced severe bleeding after using the substance, officials with the Illinois Department of Public Health said in a statement. The users were hospitalized — and two of them died — after coughing up blood, finding blood in their urine or bleeding from their noses or gums, officials said.

State health officials are struggling to find the source and a way to stop it.

“While there have been cases of adverse effects from synthetic cannabinoids, we have not seen the severe bleeding on this scale,” Melaney Arnold, a spokeswoman for the Illinois Department of Public Health, said Tuesday in a statement to The Washington Post. “We continue to investigate cases as they come in to try to identify what product they may have used and where they obtained it. However, synthetic cannabinoids are unregulated and identifying a source or sources is difficult.

An owner of a Chicago convenience store and two employees have been charged with selling the substance, containing rat poison, which has been linked to the reported deaths.

Federal prosecutors have charged 48-year-old Fouad Masoud and 44-year-old Jad Allah, both of suburban Justice, and 44-year-old Adil Khan Mohammed of Chicago with conspiring to distribute and sell a controlled substance. Federal prosecutors say U.S. Drug Enforcement Administration agents made undercover buys of the synthetic cannabinoids at Masoud’s West Side Chicago store.

Federal officials say synthetic cannabinoids were packaged in sealed containers and labeled with such names as ‘Matrix,’ ‘Blue Giant,’ and ‘Crazy Monkey.’ Testing of the products revealed brodifacoum, a toxic substance frequently used in rat poison.

The packaging is designed for the teen and young adult market. A PBS News Hour video, which features three young people who consumed synthetic marijuana, offers evidence of how different the material is from the real plant.

In addition to the rat poison, the synthetic marijuana contains a compound that mimics the active ingredient in pot, but are much more aggressive in their response to the body’s receptors.

Contrary to what many think, synthetic marijuana is not one drug, and it is very different from tetrahydrocannabinol (aka THC, the main compound in natural marijuana). Synthetic marijuana is a “designer drug,” a chemical engineered to create the same effects as an illegal drug, but one that is different enough to avoid drug laws.

Synthetic cannabinoids (substances mimicking marijuana) work on the same brain receptors as THC, but can bind to the receptor up to 100 times more tightly than THC. Most were actually developed for research purposes so that scientists could better understand the role of THC receptors in the brain. Unlike marijuana, they have no reported potential for medical use. Eighty-four new synthetic cannabinoids were identified by the National Forensic Laboratory Information System in 2015 alone (for comparison, there were only two in 2009). These chemicals, all vastly different from each other, do not cause identical responses in the brain.

And because the “drug” is actually a highly variable mixture, the effects of the body can be quite different even if the same “brand” is used.

First and foremost, these are “psychoactive” substances, which cause an altered mental perception of the world. This high can be associated with irritability, confusion, sleepiness, dizziness and inability to concentrate. At worst, they cause hallucinations (fives times more often than THC), suicidal thoughts and violent behavior. They are also far more likely than marijuana to cause other symptoms like vomiting and muscle breakdown. They can lead to heart problems such as fast heart rate, high blood pressure and even heart attacks. There have been reports of rapid and complete kidney failure related to specific strains of synthetic marijuana.

Hopefully, there will be no more deaths from this material. It’s not as if there isn’t plenty of ways to die horribly in Chicago already.