PORTLAND, Ore. – Fentanyl is an incredibly dangerous drug that causes tens of thousands of overdose deaths in the United States on a yearly basis. According to the Centers for Disease Control and Prevention, fentanyl is 50 times stronger than heroin and 100 times stronger than morphine. Now, a new study published in BMJ Case Reports reveals how much more terrifying this synthetic opioid can be. Doctors from Oregon Health and Science University (OHSU) have documented the first known instance of toxic leukoencephalopathy, a rare type of brain damage resulting from the inhalation of fentanyl.