3-Methylfentanyl (3-MF, mefentanyl) is an opioid analgesic that is an analogue of fentanyl. 3-Methylfentanyl is one of the most potent drugs that has been widely sold on the black market, estimated to be between 400-6000 times stronger than morphine depending on which isomer is used (with cis isomer being the more potent one). 3-Methylfentanyl was first discovered in 1974 and subsequently appeared on the street as an alternative to the clandestinely produced fentanyl analogue α-methylfentanyl. However it quickly became apparent that 3-methylfentanyl was much more potent than α-methylfentanyl, and corespondingly even more dangerous.