Molecular model of the synthetic opioid analgesic (painkiller) mefentanyl, or 3-methylfentanyl, an analogue of fentanyl. It is a highly potent form of the drug and is estimated to be 400 to 6000 times stronger than morphine. Recreational use often results in lethal overdoses. Atoms are represented as spheres and are colour-coded: carbon (black), hydrogen (white), nitrogen (blue) and oxygen (red).