Cychlorphine The New Synthetic Opioid Threat
Cychlorphine: The New Synthetic Opioid Behind a Wave of Overdose Deaths
I don't know whether I've ever treated a patient who used cychlorphine. Currently, no hospital drug screen in the country looks for this substance. Fentanyl and nitazene test strips don't catch it. Every doctor treating opioid overdose in America is in the same position. So when you read that cychlorphine has been found in a few hundred cases nationally, understand that the number is out of the cases somebody thought to test for this new opioid.
What Is Cychlorphine?
Cychlorphine, chemically named N-propionitrile chlorphine, is a synthetic opioid that has never been approved for any medical use anywhere. It was made in a lab to be sold, and nothing else. It works on the mu-opioid receptor, the same target as heroin, morphine and fentanyl. That means it does what opioids do. It relieves pain, it sedates and it slows your breathing until it stops.
Cychlorphine belongs to a group called the benzimidazolone opioids, sometimes called the orphine analogs. Robert Raffa and colleagues, writing in the Journal of Pain Research in July 2026, are direct about the classification: cychlorphine is not a fentanyl, nitazene, or morphinan derivative. It's a distinct chemical class with its own lineage, related to a 1967 Janssen patent on piperidine benzimidazolones and to brorphine, which showed up in illicit drug supply in 2019 and was internationally controlled in 2022.
You'll see the claim that cychlorphine is 10 times stronger than fentanyl. Treat that as an estimate, because that's all it is. What has actually been measured is how tightly the related compound chlorphine grabs the opioid receptor, and the number there is a binding constant of 1.92 nanomolar against fentanyl's 6.29. Lower means tighter. It holds on harder than fentanyl does. So it is a very powerful synthetic opioid threat whose exact potency in humans nobody has established, because establishing that would take human studies that never happened. But what this means is overdoses require multiple doses of naloxone to reverse the effects.
Where Cychlorphine Came From
In July 2025, the Chinese government placed generic controls on nitazenes, an older family of synthetic opioids. Generic controls ban a whole chemical scaffold instead of one molecule at a time, so they close loopholes that individual bans leave open. Within months, forensic labs watched nitazene-positive cases fall and a structurally different class rise to take the space in the drug market. Cychlorphine led that shift. Donna Papsun and colleagues documented this pattern after fentanyl-related substances were scheduled as a class, showing that banning one opioid scaffold reliably predicts the arrival of the next unscheduled one in postmortem casework. Banning a molecule does not shrink the market. It only changes what fills the space and this highly potent synthetic opioid is an emerging threat.
Cychlorphine is currently not federally scheduled in the United States by the Drug Enforcement Administration (DEA). Whether the Federal Analog Act reaches benzimidazolone structures has not been settled.
What Cychlorphine Is Doing Right Now
A DEA laboratory in Florida made the first United States detection in April 2024. The Center for Forensic Science Research and Education first detected it in August 2024 and confirmed it that September.
Detections stayed sporadic for about a year before climbing sharply in late 2025. The Center for Forensic Science Research and Education reported finding N-propionitrile chlorphine in 25 blood specimens from fatal overdoses, 21 in the United States and 4 in Canada, with the large majority submitted in the last quarter of 2025 and the first months of 2026. It was the only opioid found in 11 of those 25 cases. NMS Labs has tentatively identified it in more than 100 toxicology cases. As of March 2026, at least 24 states had reported overdoses or deaths linked to it.
East Tennessee has been hit hardest. The Knox County Regional Forensic Center linked nine overdose deaths to it from late October through December 2025, then seven more by the middle of January. Chris Thomas, the center's director, described what he was watching in February: "It's showing up at an exponential rate and at this point, we don't know if it's a single batch and done with or if it's the new future."
The Tennessee cases started in Knox County and spread into Roane, McMinn, Campbell, Union, Anderson, Claiborne and Sevier counties. Most involved methamphetamine and fentanyl as well. By March the Tennessee Department of Health counted more than 30 fatal overdoses statewide. In January a University of Kentucky harm reduction program found cychlorphine in a syringe from Fayette County, less than a three-hour drive from Knoxville.
The United Nations Office on Drugs and Crime added orphine analogs to its early warning system as a formal new structural group in February 2026, citing detections across 14 countries. Oklahoma health officials are watching for it. So am I.
It Has No Street Name Because Nobody Is Asking for It
I went looking for what people call this on the street and found nothing at all, which tells you something about how it reaches people.
The only published human case of a cychlorphine overdose is a 36-year-old man described by Jon Sprague and colleagues at Bowling Green State University. He was found unconscious and not breathing on a bathroom floor. When he came around, he told the treating team he had snorted a substance he believed was alprazolam. He thought he was taking Xanax. Crime scene investigators recovered a small bag of tan crystallized powder. Laboratory analysis found three drugs in it: fentanyl, xylazine and cychlorphine. Cychlorphine was the largest component.
Nobody is asking a dealer for cychlorphine, so nobody needed to invent a word for it yet. It arrives inside something else. In confirmed cases it has turned up alongside fentanyl, oxycodone, methamphetamine, cocaine, carfentanil and novel benzodiazepines, which means anyone taking an illicit pill or powder right now is already exposed to it.
Why Nothing You Own Will Detect It
Standard hospital immunoassay drug screens were designed around morphine, oxycodone and fentanyl. They do not detect benzimidazolone opioids. A person can be dying of cychlorphine and produce a completely negative opioid screen. Fentanyl and nitazene test strips miss it as well, because neither cross-reacts with orphine analogs. Confirming it takes liquid chromatography with mass spectrometry and a validated reference standard for that specific molecule, which most hospitals cannot run and which forensic labs are still building out.
The practical consequence for clinicians and families is that a negative opioid screen in someone with unexplained sedation and slow breathing rules nothing out, so treat what is in front of you. For anyone using, the strips are still worth carrying, since fentanyl remains the bigger killer and they do catch that.
Does Naloxone Work on Cychlorphine?
You may have read that it doesn't. That claim is being repeated by news outlets, by law enforcement trade publications and by treatment centers, and the evidence behind it does not hold up. Marthe Vandeputte and colleagues published animal work on brorphine analogs in 2024, and in that study naloxone given as a pretreatment did not completely block the pain-relieving effects of chlorphine.
That wording resurfaced in the Knox County media release from February 2026, where chief medical examiner Darinka Mileusnic-Polchan said that "naloxone, or Narcan, does not completely block the effects of the drug and multiple doses may be needed to prevent an overdose." Thus, the risk of overdose is really high with cychlorphine.
By the time the press learned about the drug, it had hardened into headlines warning that the drug resists naloxone. Along the way a finding about chlorphine got applied to cychlorphine, which is a different compound, and a blocking experiment got reported as though it were a rescue experiment. Giving an antagonist beforehand to see whether it prevents an effect answers a completely different question from giving it afterward to reverse an overdose. Raffa and colleagues call this out directly, writing that the distinction has been misrepresented in some public health advisories and that there is currently no published clinical evidence that naloxone fails to reverse cychlorphine overdose.
The pharmacology points the other way. Cychlorphine is a full agonist at the mu-opioid receptor with no meaningful biased signaling, which means naloxone should displace it the way naloxone displaces any other opioid at that receptor.
The one human case supports that. Law enforcement gave the man on the bathroom floor 4 milligrams of intranasal naloxone and got a partial response, paramedics gave another milligram, and he reached the emergency department bradycardic and hypothermic but rousable and alive. That partial response is worth reading carefully, because his powder also contained xylazine and fentanyl, and naloxone has never reversed xylazine. A partial response in a three-drug overdose is what you would expect even if the naloxone worked perfectly on the opioids.
Raffa's team makes the same argument about the fatal cases. Cychlorphine keeps showing up with benzodiazepines and stimulants, and naloxone does not touch benzodiazepine-driven sedation or respiratory depression. That explains apparently naloxone-resistant deaths without requiring the drug to be resistant to anything.
The Tennessee Department of Health, working in the state with the largest cluster in the country, reached the same conclusion in March 2026. Their guidance is that naloxone is effective with cychlorphine though it may require repeat dosing, so give it, provide rescue breaths and repeat if the person doesn't respond or their breathing slows again.
So carry naloxone and use it. The realistic concern with a drug this potent is that one dose may not be enough, which is exactly the situation with high-potency fentanyl analogs and exactly what emergency responders already train for. Believing that Narcan is useless here could get somebody killed, and that belief is not supported by anything published.
What Happens After the Reversal
Naloxone buys minutes without treating anything underneath it. In the hospital, the approach to a potent synthetic opioid is different from what happens on a sidewalk. Rather than pushing a large dose all at once, we titrate naloxone in small increments, often 0.04 milligrams every 10 to 20 seconds, until the person is breathing well enough on their own. The goal is adequate breathing, not full wakefulness, because slamming somebody into abrupt withdrawal creates its own problems. If they don't respond, or their airway is at risk, they get intubated. Out in the field with an intranasal kit you do not have that kind of control, which is exactly why you give a dose, support breathing and repeat.
Somebody who survives a cychlorphine overdose and has opioid use disorder still has substance use disorder an hour later, and now they may have a dose of naloxone on board that has thrown them into withdrawal. They need to consider long term treatment.
Buprenorphine is the treatment that keeps people alive, and starting it after exposure to a high-potency synthetic opioid is genuinely tricky. We learned this the hard way with fentanyl, which can sit in body tissue long enough that a standard buprenorphine start throws the patient into precipitated withdrawal. Buprenorphine binds the mu-opioid receptor tightly but only partially activates it, so it can shove a full agonist off the receptor and drop the person into sudden, severe withdrawal if the timing is wrong.
Nobody knows yet whether cychlorphine behaves like fentanyl in this respect. There is no published data on buprenorphine induction after a cychlorphine exposure. I would approach it the way I approach a fentanyl-exposed patient: assume the drug may linger, wait for real withdrawal before starting, and consider a low-dose start. Anyone in this situation needs an addiction medicine physician rather than a guess.
The Overdose Numbers Are Falling, and This Is Not Over
American overdose deaths have now dropped three years running. The CDC counted an estimated 69,973 deaths in 2025, down almost 14 percent from 81,313 the year before. Opioid-involved deaths fell from about 55,296 to 44,564. Those are real people who are still alive, and the naloxone distribution, buprenorphine access and fentanyl test strips that got us there deserve the credit.
During those same falling months, a drug almost nobody had heard of two years earlier was linked to more than 30 deaths in Tennessee alone, and to fatal overdoses in at least 24 states. I have watched this cycle repeat my entire career, and it has a well-described shape. The first wave started in the 1990s with prescription opioid pain relievers. The second began around 2010 and ran on heroin. The third started in 2013 and belonged to illicitly manufactured fentanyl and its analogs. Many of us now talk about a fourth wave defined by polysubstance use, with stimulants turning up alongside the opioids, which is exactly what East Tennessee toxicology is finding.
Cychlorphine looks like the leading edge of whatever comes next. Fentanyl analogs got scheduled as a class, and nitazenes filled the opening. China controlled nitazenes in July 2025, and here we are. Every time we close one door a chemist opens another, usually inside a year.
The overdose curve going down is a genuine public health win and I'll take it. It is also the exact moment when attention and funding start to drift, and the next wave arrives while everyone is congratulating themselves.
Expect the next one and plan for it. That is the theme of the rest of my career and probably yours.
What to Do
If you use any illicit drug, assume there's an opioid in it and never use alone. Keep naloxone within arm's reach and make sure the person you're with knows where it is and how to use it. Plan on needing more than one dose. Keep using fentanyl test strips for what they can catch.
If you find someone unresponsive and breathing slowly or not at all, call 911, give naloxone, and wait for further instruction from the 911 operator. Opioids kill by switching off the part of the brainstem that notices carbon dioxide building up in your blood. Normally that rising carbon dioxide is what makes you take your next breath without thinking about it. An opioid mutes that alarm, so the person simply stops breathing, and what actually kills them is the lack of oxygen that follows. Naloxone can restore the alarm. Rescue breaths keep oxygen going to the brain while you wait for it to work, and brain cells start dying in minutes.
If you have opioid use disorder, treatment works and it works better than it did ten years ago. Buprenorphine and methadone cut the risk of dying, and that effect is not subtle. Anybody who tells you that medication is trading one addiction for another is repeating something that the evidence retired a long time ago.
If you are worried about a family member, say the word "cychlorphine" to their treating physician, tell the emergency department they may have taken something bought illicitly, and do not accept a negative opioid screen as proof that nothing happened.
If you are in Tulsa or anywhere in Oklahoma, Texas, Arizona, Louisiana, Missouri or Florida, you can reach me at 918-518-1636 to talk about treatment.
Frequently Asked Questions
What is cychlorphine?
Cychlorphine, also called N-propionitrile chlorphine, is a synthetic opioid never approved for medical use. It belongs to the benzimidazolone family, also known as orphine analogs, and is chemically distinct from fentanyl and from nitazenes. It acts on the mu-opioid receptor and causes sedation and respiratory depression like other opioids. It has been linked to overdose deaths in at least 24 states.
Does Narcan work on cychlorphine?
Yes, based on the available evidence. Reports that naloxone fails against cychlorphine trace back to an animal study where naloxone was given as a pretreatment rather than as a rescue, and that study looked at a related compound rather than cychlorphine itself. The Tennessee Department of Health advises that naloxone is effective but may require repeat dosing. Give naloxone, give rescue breaths and repeat every two to three minutes until the person responds.
Is cychlorphine stronger than fentanyl?
It is often described as roughly ten times more potent than fentanyl, but that figure is an estimate rather than a measured value in humans. What has been measured is receptor binding affinity, where the closely related compound chlorphine binds more tightly than fentanyl does. It is a very potent opioid, and a dose small enough to be invisible can be fatal.
Will a drug test detect cychlorphine?
Usually not. Standard hospital urine screens are built around morphine, oxycodone and fentanyl and do not detect benzimidazolone opioids. Fentanyl test strips and nitazene test strips do not cross-react with it either. Confirming cychlorphine requires liquid chromatography with mass spectrometry using a validated reference standard, so overdose deaths involving it are almost certainly undercounted.
What does cychlorphine look like and what is it sold as?
There are no established street names for it, because people are not buying it on purpose. It has been found in tan crystallized powder and mixed into counterfeit pills. In the only published human overdose case, the man believed he was snorting Xanax. It has also been detected alongside fentanyl, xylazine, methamphetamine, cocaine, oxycodone and carfentanil.
References
Raffa RB, Breve F, Pergolizzi JV Jr, Vortsman E, Varrassi G. Cychlorphine (N-propionitrile chlorphine): an emerging benzimidazolone synthetic opioid and its implications for overdose recognition and management. J Pain Res. 2026;19:620907. doi:10.2147/JPR.S620907
Sprague JE, Toms JA, Ratermann CF. Non-fatal opioid overdose associated predominantly with the benzimidazolone, cychlorphine. Clin Toxicol (Phila). 2026;64(2):146-147. doi:10.1080/15563650.2025.2594070
Vandeputte MM, Bilel S, Tirri M, et al. Elucidating the harm potential of brorphine analogues as new synthetic opioids: synthesis, in vitro, and in vivo characterization. Neuropharmacology. 2024;260:110113. doi:10.1016/j.neuropharm.2024.110113
Papsun DM, Krotulski AJ, Logan BK. Proliferation of novel synthetic opioids in postmortem investigations after core-structure scheduling for fentanyl-related substances. Am J Forensic Med Pathol. 2022;43(4):315-327. doi:10.1097/PAF.0000000000000787
Center for Forensic Science Research and Education. Increase in fatal overdoses linked to novel synthetic opioid n-propionitrile chlorphine (cychlorphine). Public Alert. January 2026.
United Nations Office on Drugs and Crime. Early warning advisory: increasing nitazene and orphine analogues (synthetic opioids). 2026.
Tennessee Department of Health. TDH reinforces importance of naloxone with rise in cychlorphine fatalities. March 18, 2026.
Knox County Regional Forensic Center. Preliminary tests link 16 deaths to new drug. Media release. February 5, 2026.
National Center for Health Statistics, Centers for Disease Control and Prevention. U.S. overdose deaths decrease for third consecutive year in 2025. May 13, 2026.
Medrano K. No, synthetic opioid cychlorphine has not proved Narcan "ineffective." Filter. March 5, 2026.
About the author:
Harold Pierre, MD, is a board-certified anesthesiologist, board-certified addiction medicine specialist, and a concierge addiction doctor with over 27 years of experience. He is board-certified by the American Board of Anesthesiology, the American Board of Preventive Medicine and has extensive experience managing hormones. He is licensed in Florida, Texas, Oklahoma, Missouri, Louisiana, and Arizona. If you are seeking care, you may schedule an appointment with him by calling or texting 918-518-1636. LinkedIn
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