Something to look forward to: In the search for safer alternatives to traditional pain medications, scientists at the National Institutes of Health have identified a new synthetic compound that could transform opioid therapy. Their findings, published in Nature, describe an experimental drug that provided strong analgesia in laboratory animals without causing the respiratory depression or dependence that have long defined the risks of opioids.
The study focuses on DFNZ, a molecule derived from a class of synthetic opioids first explored in the mid-20th century but largely abandoned due to their high potency. This research revisits nitazenes using modern pharmacological tools and aims to redesign them for greater safety. Investigators say the results represent unexpected progress in balancing efficacy with reduced abuse potential.
"Opioid pain medications are essential for medical purposes, but can lead to addiction and overdose," said Nora D. Volkow, director of NIH's National Institute on Drug Abuse. "Developing a highly effective pain medication without these drawbacks would have enormous public health benefits."
The NIH team began by examining FNZ, a precursor compound that can be tracked in the brain using positron emission tomography imaging. This technique revealed that FNZ remains in the brain for only minutes, yet its pain-relief effects persist for hours. That discovery led researchers to a metabolite, DFNZ, that proved unexpectedly potent at the mu opioid receptor, the primary target of most opioid drugs.
"Our goal was to study the profile, or pharmacology, of these drugs," said Michael Michaelides, senior author and NIDA investigator. "We wanted to decrease the potency and create a potential therapeutic. What we discovered exceeded our expectations."
While FNZ itself carries the typical risks of opioids – namely, respiratory depression and high abuse potential – DFNZ appeared to operate differently in early tests. At therapeutic doses, it increased brain oxygen levels rather than suppressing breathing, and repeated administration did not result in tolerance or significant withdrawal symptoms. Among 14 standard indicators of withdrawal observed in rats, only mild irritability was recorded.
To investigate whether DFNZ might still reinforce drug-seeking behavior, researchers trained rats to press a lever for doses of the compound. The animals self-administered DFNZ, indicating its capacity for reward. However, when the drug was replaced with saline, the animals quickly lost interest – a contrast to the persistent seeking behavior seen with morphine, fentanyl, or heroin.
Further analysis pointed to activity in the brain's dopamine system. DFNZ produced slow, steady increases in dopamine rather than the sharp spikes associated with strong reinforcement and craving. This pattern may help explain its reduced addictive potential.
Michaelides noted that DFNZ exhibits a distinctive pharmacological profile compared with other opioids. While it provides strong pain relief, it behaves in some ways like partial agonists – compounds that activate opioid receptors to a lesser degree – a feature associated with improved safety. He added that DFNZ's ability to deliver therapeutic effects without suppressing breathing is a particularly significant finding.
The findings challenge longstanding assumptions about how mu opioid receptor agonists behave. If further tests confirm the compound's pharmacological advantages, DFNZ could represent a rare combination of robust pain relief and safety – qualities that may also make it useful for treating opioid use disorder itself.
The NIH team plans to extend its preclinical work to support regulatory pathways for human testing. Researchers see potential applications in surgical, cancer-related, and chronic pain, where existing opioids carry serious risks of overdose or dependence.
NIH study identifies experimental opioid with strong pain relief and lower addiction risk
