FILE - In this June 29, 2016 file photo, a man holds a bag of synthetic marijuana in Houston. In a report released Tuesday, April 10, 2018, fake marijuana likely contaminated with rat poison has killed three people in Illinois and sickened more than 100 others in the past month. (Melissa Phillip/Houston Chronicle via AP)

FILE - In this June 29, 2016 file photo, a man holds a bag of synthetic marijuana in Houston. In a report released Tuesday, April 10, 2018, fake marijuana likely contaminated with rat poison has killed three people in Illinois and sickened more than 100 others in the past month. (Melissa Phillip/Houston Chronicle via AP)

Fake marijuana likely contaminated with rat poison has killed three people in Illinois and caused severe bleeding in more than 100 others, including a few in four other states.

The federal Centers for Disease Control and Prevention has alerted doctors nationwide that patients with severe, unexplained bleeding may be additional cases.

The CDC is helping Illinois authorities investigate the outbreak in that state, which began in early March. Illinois reported seven more cases on Tuesday, bringing the nationwide total to at least 116.

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Several patients and samples of so-called synthetic marijuana from Illinois have tested positive for a lethal ingredient often used in rat poison, the CDC and Illinois authorities said.

Symptoms include coughing up blood, blood in the urine, severe bloody noses, bleeding gums and internal bleeding. CDC’s alert says outside Illinois, emergency rooms in Indiana, Missouri, Wisconsin and Maryland have treated affected patients since March 10.

Illnesses have been linked to fake marijuana before but this is the first outbreak involving rat poison contamination, said the CDC’s Renee Funk. Those sickened require hospitalization and treatment with vitamin K to control bleeding, she said.

“This is an unusual outbreak,” Funk said Tuesday, adding that is unclear how the contamination occurred.

Fake marijuana, also called synthetic cannabinoids, contains man-made chemicals that produce a high similar to marijuana. It is sold in smoke shops and other stores as liquids that can be used in e-cigarettes or in dried plant material that can be smoked. Nicknames include K2, Spice and Kush.

“The number of cases continues to go up each day,” Melaney Arnold, spokeswoman for the Illinois Department of Public Health, said Tuesday. “Synthetic cannabinoids in general are not safe and this is one example of not knowing what chemicals are in the product. We are telling people don’t use synthetic cannabinoids.”

The federal government and many states have banned some of these products or specific ingredients, but the CDC says manufacturers skirt these laws by creating new products or labeling them “not for human consumption.”

Tests on fake pot bought at a Chicago convenience store by undercover agents detected the rat poison ingredient, the U.S. attorney’s office said in a news release. Three store employees were arrested and face federal drug charges.

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Illnesses from fake marijuana have increased in recent years; a CDC report noted at least 456 cases between 2010 and 2015. The products are up to 100 times more potent than the active ingredient in marijuana and severe reactions have included seizures, coma and delirium.

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Follow AP Medical Writer Lindsey Tanner on Twitter at @LindseyTanner. Her work can be found here .

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The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.