Norfentanyl is an inactive synthetic opioid analgesic drug precursor.

[2] It is an analog and metabolite of fentanyl with the removal of the phenethyl moiety (or functional group) from fentanyl chemical structure.

[3][4][5][6][7][8][9][10] Norfentanyl occurs primarily as a metabolite of its parent drug, fentanyl.

However, it can also be used to synthesize fentanyl itself.