LAUSR

Itch Spinal and epidural morphine administration is used in the clinical setting as an analgesic for surgical procedures and in women during labor. However, delivery through these routes is associated with the development of itch. The molecular basis of this unwanted side effect has been unclear. Nguyen et al. found that morphine-induced itch did not involve mast cells but rather was mediated by the activity of spinal dynorphin neurons and subsequent inhibition of kappa-opioid receptor–expressing neurons in mice. Concomitant administration of morphine and nalfurafine, a selective kappa-opioid receptor agonist, inhibited itch without affecting morphine's analgesic properties in mice and monkeys, suggesting that this approach might also be effective in the clinical setting. Sci. Transl. Med. 13 , eabc3774 (2021).