The Cuyahoga County medical examiner has issued a warning for heroin users: He is seeing cases in which fentanyl is substituted for heroin with deadly consequences.

According to a news release from Medical Examiner Dr. Thomas P. Gilson, three suspected heroin overdose deaths occurred Tuesday and another five nonfatal suspected heroin cases were reported by the Cuyahoga County Sheriff's Office Monday and Tuesday.

The ongoing public health threat includes cases in which fentanyl has been detected, according to Gilson.

Fentanyl is an opioid analgesic pain reliever that is about 80 times the strength of heroin and has recently resulted in increased deaths of heroin users in both Pittsburgh and Lorain County.

The medical examiner's regional forensic science laboratory is on high alert to expedite testing and coordinate data sharing with law enforcement.