4-Phenyl-2-[2-(1-pyrrolidinyl)ethyl]-6-[3-(trifluoromethyl)phenyl]-3(2H)-pyridazinone-d8 is deuterium labelled form of 4-Phenyl-2-[2-(1-pyrrolidinyl)ethyl]-6-[3-(trifluoromethyl)phenyl]-3(2H)-pyridazinone (P998430), which is diaryl pyridazinone based compound with analgesic properties.