Carfentanil serves Carfentanil is an analogue of the popular synthetic opioid analgesic fentanyl, and is one of the most potent opioids known (also the most potent opioid used commercially). It has a quantitative potency approximately 10,000 times that of morphine and 100 times that of fentanyl, with activity in humans starting at about 1 microgra