To obtain a TNF production inhibitor efficiently suppressing TNF production, and useful for treatment of e.g. cancer, rheumatoid arthritis by including a specific morphine derivative (acid-added salt) as an active ingredient.

This inhibitor comprises a morphine derivative or its pharmacologically accetable acid-added salt thereof expressed by the formula (R1 is H or a lower alkanoyl; R2 is a lower alkanoyl) as an active ingredient, such as 3-acetyl-6β-acetylthio-N-cyclopropylmethyl-normorphine. The daily dose of the morphine derivative (acid-added salt) of the formula is preferably 0.02-10 mg/kg body weight per adult.