MORGANTOWN, W.Va. (AP) — A West Virginia University neuropsychologist says fentanyl not only puts street drug users at risk for opioid overdoses, it may cause amnesia.

Marc Haut, who chairs the WVU School of Medicine's Department of Behavioral Medicine and Psychiatry, has published a case report in the Annals of Internal Medicine about the potent drug, considered 50 to 100 times more potent than morphine.

His report links fentanyl use with a particular form of sudden amnesia that produces distinctive results noted in brain scans.

Haut's collaborator Jed Barash, medical director at Soldiers' Home in Burlington, Massachusetts, previously detected a cluster of that amnesia among drug users in Massachusetts.

They have now used lab testing and neuroimaging to support the theory that fentanyl use may trigger it in some people.