BELLEVILLE, Ill. (AP) – A narcotic painkiller has been removed from all ambulances in the Belleville area as a state regulator and police investigate “unauthorized tampering” of the drug.

The Belleville News-Democrat reports that Dr. Savoy Brummer ordered emergency medical services in the region earlier this year to turn over supplies of fentanyl. The Memorial Hospital physician also decreed that each instance where fentanyl was administered from May 2013 to May 2015 be documented.

Brummer and Memorial serve as regional state regulators of ambulances.

Memorial spokeswoman Anne Thomure says the hospital is cooperating with a police investigation of alleged tampering but would not elaborate.

Fentanyl is a synthetic opiate used as a painkiller and is effective in patients who have built up a tolerance to similar drugs such as morphine.