Summary: Researchers at the National Institutes of Health (NIH) report the discovery of a high-potency opioid with an unusually favorable safety profile in preclinical studies. Derived from an overlooked class of 1950s synthetic compounds called nitazenes, this compound’s metabolite—called DFNZ—provides strong and long-lasting pain relief while appearing to avoid two of the most dangerous opioid liabilities: respiratory depression and the rapid, intense dopamine signaling that drives addiction.
Unlike the parent compound (FNZ), which carries serious risks, DFNZ behaves as a mu-opioid “superagonist” with a distinct pharmacology: it produces extended analgesia even though the parent drug clears the brain quickly, it does not depress respiration in the tested animal models, and it elicits a slower dopamine response that seems less likely to create powerful drug-cue associations. These findings challenge the longstanding assumption that greater opioid efficacy necessarily means greater danger.
Key Facts
- Nitazenes revisited: Nitazenes were largely set aside in the 1950s because of their extreme potency. Modern pharmacological tools allowed the NIH team to re-examine this class and identify DFNZ, a metabolite that selectively and potently activates the mu-opioid receptor while showing a distinct safety profile.
- Respiratory safety signal: In rodent models and at therapeutic doses, DFNZ did not depress breathing; in fact, investigators observed a modest increase in brain oxygen levels rather than the respiratory suppression typical of fentanyl or high-dose morphine.
- Reduced addiction-like behavior: In self-administration experiments, rats that had been pressing a lever for DFNZ stopped pressing almost immediately when the drug was replaced by saline. This contrasts with persistent drug-seeking seen with heroin, fentanyl, or morphine in similar tests.
- Dopamine timing matters: Neurochemical analysis showed that DFNZ increases dopamine in the brain’s reward circuits gradually rather than triggering rapid bursts. The slower dopamine dynamics appear to produce relief and mild reward without forming the strong conditioned responses that fuel craving and relapse.
Source: NIH
Overview of the study
The NIH team published their results in Nature after testing the drug’s effects in rodents. Their experiments combined behavioral assays, positron emission tomography (PET) imaging, pharmacology, and neurochemical measurements. PET imaging showed that the parent compound FNZ entered the brain only briefly—about five to ten minutes—yet analgesia lasted for at least two hours. That discrepancy prompted the search for active metabolites and led to identification of N-desethyl-fluornitrazene (DFNZ).
At clinically relevant dosing in animals, DFNZ produced potent analgesia without signs of respiratory depression, tolerance, or meaningful withdrawal after repeated exposure. Among standard measures of opioid withdrawal, investigators observed only a transient increase in irritability-related vocalizations in handled animals. In drug self-administration procedures, animals did find DFNZ rewarding but abandoned drug-seeking quickly when the drug was removed, unlike the persistent seeking typical of more addictive opioids.
Mechanistically, DFNZ shows limited brain penetrance and a unique mu-opioid receptor signaling profile, including altered interactions with receptor heteromers such as MOR–GAL1. These properties appear to underlie the compound’s combination of high analgesic efficacy and low adverse-effect liability in preclinical tests.
The authors emphasize that these results come from preclinical animal studies. The next steps are additional preclinical work to support regulatory filings for human trials. If human studies confirm these findings, DFNZ or related nitazene-derived molecules could offer new options for surgical, cancer-related, and chronic pain management, and might also be explored as a therapy for opioid use disorder with potentially lower risk of respiratory depression than existing agonist treatments.
Funding: This research was supported in part by the NIH Intramural Research Program and NIH/NIDA grant DA056354.
Key Questions Answered
A: Addiction risk depends on more than potency. Rapid, high-amplitude dopamine spikes in reward circuits create strong learned associations and craving. DFNZ promotes a slower, sustained dopamine signal that appears to relieve pain and provide some reward without producing the intense spikes that drive compulsive seeking.
A: Standard opioids can inhibit brainstem centers that control breathing. DFNZ’s pharmacology appears to engage mu-opioid receptors in a way that avoids activating the secondary pathways responsible for respiratory suppression, producing a different physiological outcome in the animal models tested.
A: The compound is currently at the preclinical stage. The research team is pursuing further studies to support applications for human clinical trials. Any timeline for human availability depends on the outcomes of those trials and regulatory review.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The full journal paper was reviewed for accuracy.
- Additional contextual information was added by editorial staff.
About this neuropharmacology research news
Author: NIH Office of Communications
Source: NIH
Contact: NIH Office of Communications – NIH
Image: Image credited to Neuroscience News
Original Research: Open access. “A μ opioid receptor superagonist analgesic with minimal adverse effects” by Juan L. Gomez, Emilya N. Ventriglia, Zachary J. Frangos, Agnieszka Sulima, Michael J. Robertson, Michael D. Sacco, Reece C. Budinich, Ilinca M. Giosan, Tongzhen Xie, Oscar Solis, Anna E. Tischer, Jennifer M. Bossert, Kiera E. Caldwell, Hannah Bonbrest, Amelie Essmann, Zelai M. Garçon-Poca, Shinbe Choi, Michael R. Noya, Feonil Limiac, Ali Arce, Grant C. Glatfelter, Margaret Robinson, Li Chen, Angelina A. Mullarkey, Dain R. Brademan, Garrett Enten, William Dunne, César Quiroz, Ingrid Schoenborn, Chae Bin Lee, Rana Rais, Daniel P. Holt, Robert F. Dannals, Lei Shi, Ruth Hüttenhain, Sergi Ferré, Eugene Kiyatkin, Jordi Bonaventura, Yavin Shaham, Venetia Zachariou, Michael H. Baumann, Georgios Skiniotis, Kenner C. Rice & Michael Michaelides. DOI: 10.1038/s41586-026-10299-9
Abstract
A μ opioid receptor superagonist analgesic with minimal adverse effects
Developing safe and effective pain medications remains a critical challenge. Agonists of the μ-opioid receptor (MOR) are highly effective analgesics but often cause respiratory depression, constipation, tolerance, dependence, withdrawal and addiction. Traditional strategies to limit adverse effects include designing MOR agonists with lower intrinsic efficacy or with signaling bias toward G-protein versus β-arrestin pathways.
This study identifies a novel MOR agonist with supramaximal intrinsic efficacy and an uncommon pharmacological signature that produced strong analgesia in rodents with minimal adverse effects. N-desethyl-fluornitrazene (DFNZ), derived from nitazene benzimidazole opioids, displays reduced brain penetrance, a distinctive spatiotemporal MOR signaling profile, and lower efficacy at the MOR–GAL1 heteromer. In preclinical testing, DFNZ did not induce respiratory depression, tolerance, or MOR downregulation after repeated exposure, and it produced limited dopamine effects in the nucleus accumbens and weaker reinforcing effects in self-administration assays. These results provide new insight into MOR and nitazene pharmacology and suggest that high-efficacy MOR agonists can, in certain cases, be developed with improved safety profiles for pain and addiction treatment.