People who suffer from chronic itching say it's more unbearable than pain. I'll never forget a 2008 story called The Itch in The New Yorker. It's about a woman whose scalped itched so much that "She had scratched through her skull during the night—and all the way into her brain."
Chemical and Engineering News reports that a compound in the popular psychedelic plant Salvia divinorum was found to contain a compound that is found to provide itch relief to mice.
Salvinorin A, a hallucinogen produced by the Mexican plant Salvia divinorum, holds promise for treating itch and pain because it activates the κ-opioid receptor while avoiding the μ-opioid receptor, a sister receptor that’s been associated with opioid abuse. Chemists have tried to synthesize salvinorin A so that they could alter the structure to sidestep the compound’s psychoactive effects while preserving its analgesic properties. But salvinorin A’s scaffold has been challenging to recreate.
Now, a team of scientists at the California and Florida branches of Scripps Research Institute, as well as at the University of Southern California, report a 10-step total synthesis of 20-norsalvinorin A (ChemRxiv 2017, DOI: 10.26434/chemrxiv.5318188). The compound differs from salvinorin A by a single methyl group and binds to the κ -opioid receptor with an affinity similar to that of the natural product. When given to mice, it also provides itch relief.