PURPOSE: To provide the titled inhibiting agent containing benzaldehyde or 4,6-O- benzylidene-D-glucose as active component, effective to specifically suppressing encephalinase, and useful as an analgesic especially for carcinomatous pain.

CONSTITUTION: Benzaldehyde or 4,6-O-benzylidene-D-glucose is used as an encephalinase inhibiting agent. Enchephalin is a peptide having the structure of formula and exhibiting analgesic activity in the brain, and is deactivated rapidly with an enzyme. It has been found newly that benzaldehyde or its D-glucose acetal, i.g. 4,6-O-benzylidene-D-glucose, is effective to specifically suppress the encephalinase A which is an encephaline decomposition enzyme, and has analgesic activity. It is used in combination with various analgesics for the pain of cancer, ulcer, lithiasis, postoperative pain, etc., or with a morphine-like analgesic to increase the activity of the analgesic.