Tuftsin and D-Arg3-tuftsin possess analgesic action

Tuftsin has marked analgesic activity but is less potent than D-Arg3-tuftsin. The absence of an antagonistic effect of naloxone on tuftsin and its analogue suggests that these substances do not act on opiate receptors. Tuftsin and its analogues may represent a new class of substances of interest in the search for new analgesics.