NIH researchers have discovered a “novel, highly potent opioid that shows potential as a therapy for both pain and opioid use disorder.”

The resultant study, published in Nature, detailed a trial’s effect in laboratory animals, showing that it has “high pain-relieving effects without causing respiratory depression, tolerance, or other indicators of potential for addiction in humans.”

The team investigated “formulations of an understudied class of synthetic opioid compounds, known as nitazenes,” which “selectively engage mu-opioid receptors.” They had been shelved since the 1950s due to their “excessive potency.” This research team aimed to harness their selectivity for the mu-opioid receptor.

The chemical formulation studied, called FNZ, entered the rats’ brains only briefly, but pain relief “persisted for at least two hours.” A so-called superagonist opioid called DFNZ was found to be responsible for the persistent pain relief. DFNZ appears to sidestep addiction-forming liabilities that scientists observed in FNZ. Rats also did not continue to attempt to get the medication after it was replaced with saline, something they do when given addictive drugs. At the same time, the animals still self-administered the drug when they had access, demonstrating some rewarding effect.