State public health officials have linked synthetic marijuana to four cases of severe bleeding that have been reported this month in northeast Illinois.

The first case was reported to the Illinois Poison Center on March 10, according to a statement released Friday by the Illinois Department of Public Health. In total, the “unusual cluster of cases” has left four people hospitalized. Each person has suffered severe bleeding from a condition that reduces the blood’s ability to clot.

All four people reported using synthetic marijuana prior to being hospitalized, according to the IDPH. The effects of synthetic marijuana, which is commonly referred to as “fake pot,” “spice,” “K2,” and “Mind Trip,” can be unpredictable and sometimes life-threatening.

The cause or source of the condition remains under investigation, the IDPH said.

Anyone who has a serious reaction to synthetic marijuana should call 911 or immediately go to an emergency room, the IDPH said. In addition, anyone with concerns about unusual bleeding should contact their healthcare provider and let them know if they have used synthetic mariuana.