Effects of the synthetic enkephalin analogue FK 33-824 on pain threshold and pain tolerance in man.

Natural enkephalins exert weak and transitory analgesic effects. The synthetic enkephalin, FK 33-824 (FK), is less susceptible to metabolic breakdown and produces long-lasting analgesia in animals. The present studies examined the effects of FK on threshold and tolerance of electrically evoked pain in man under double blind conditions.