More potent than fentanyl? 5 things to know about the illicit drug cychlorphine

After years of fentanyl causing fatal overdoses, public officials are now warning of an even more powerful opioid.

Cychlorphine (sy-KLOR-feen) is a synthetic, or lab-made, opioid — specifically, a class of drugs known as orphines. Created by researchers who were trying to find powerful painkillers in the 1960s, orphines were ultimately considered too strong and dangerous, and the U.S. Food and Drug Administration never approved cychlorphine for medical use.

Cychlorphine is a Schedule I drug that cannot be possessed or sold under federal law, but it has been increasingly linked to overdoses after China banned synthetic opioids called nitazenes.

People who track illicit drugs in the United States first identified cychlorphine in the drug supply in 2024, and Reddit users were talking about it online that same year. The drug is now making headlines in connection with U.S. overdose deaths.

It was linked to a 16-year-old’s death in San Francisco in April. And in Knoxville, Tennessee, officials said cychlorphine had been detected in about 50 suspected overdose deaths from July 2025 to early June.

Officials in Louisiana and Los Angeles County have issued public alerts warning residents of its risks as well.

How prevalent is cychlorphine in the U.S.? 

In 2024, there was one report of cychlorphine in the U.S. drug supply, according to the White House Office of National Drug Control Policy. In 2025, there were 16 reports of it in 10 states.

Nationally, orphines don’t currently appear to be widespread, but “prevalence and trends are hard to discern,” said Jason R. Williams, a research scientist at the University of Washington’s Addictions, Drug & Alcohol Institute.

Hospitals and medical examiners’ toxicology tests and even crime labs sometimes fail to detect any given drug until it becomes a substance that officials are interested in tracking or collecting data on, he said.

The National Drug Control Policy office said it is currently most prevalent in Ohio, Texas and Tennessee.

Following a fatal overdose in Los Angeles County, public health officials there warned that cychlorphine is being mixed into the illicit drug supply without people’s knowledge. It has been found in powders, rocks or crystals, liquids and counterfeit pills made to look like prescription medications, they said.

How strong is cychlorphine? 

The Drug Enforcement Administration describes fentanyl — a synthetic opioid that is approved for medical use — as about 100 times more potent than morphine.

Laboratory tests show cychlorphine is about 10 times more potent than fentanyl, said Alex Krotulski, director of toxicology and chemistry at the Center for Forensic Science Research and Education.

“That’s the only data that we have right now,” Krotulski said in July. Fentanyl has been studied in humans, but cychlorphine has not been studied in humans or animals, he said. “So we’re really finding out in real time what its effects on humans are.”

The drug’s potential effect on a person, however, depends on the dose, not just the cychlorphine’s potency.

What are the signs of a cychlorphine overdose?

The signs that a person has been exposed to a toxic amount of cychlorphine are similar to those from other opioids like fentanyl. Pupils become constricted. Breathing is slowed or shallow. And other brain and spinal cord functions such as heart rate slow as the central nervous system becomes depressed.

Even “a very small amount” of cychlorphine can cause someone to stop breathing, Los Angeles County health officials said.

Can naloxone help during a cychlorphine overdose? 

Yes, the opioid-overdose reversing drug naloxone can help.

But, much like fentanyl overdoses, cychlorphine’s potency means that treating an overdose can require multiple naloxone doses.

Naloxone usually comes in two-dose packages, meaning that when people carry it, they typically carry only one or two doses. That’s why it’s important to call 911 for suspected overdoses — first responders can provide additional doses if they’re needed.

It also might be hard to know if someone is overdosing on cychlorphine. The drug isn’t detected in routine hospital opioid urine screens or with drug test strips, so it can easily be missed.

What does data show about cychlorphine overdose rates? 

More cychlorphine overdoses are being documented, but not all labs test for it, making it hard to detect trends.

The White House Office of National Drug Control Policy reported 55 deaths linked to cychlorphine in 2025 and through April 2026.

Krotulski said the Center for Forensic Science Research and Education lab started to detect cychlorphine in late 2025, but its prevalence increased in 2026. In about seven months, the lab linked more than 140 deaths to cychlorphine in the United States and Canada, he said.

Most samples that test positive for orphines in the U.S. also test positive for other drugs, and the vast majority of orphine-related deaths also had other drugs present as well, Williams said.

That complicates determining what caused someone’s death because a toxicology panel might be limited unless evidence points toward looking for a drug not covered by typical testing, he said.

“It’s really unknown truly how many deaths there have been, but certainly in that short period of time, that is a significant number for a newly emerging drug like this,” Krotulski said.

If someone who died had a history of opioid use and the death circumstances suggest an opioid overdose but fentanyl and traditional opioids aren’t detected, then a medical examiner might test for orphines such as cychlorphine.

But if tests found fentanyl, the death would be explained and the medical examiner might not test further, potentially missing any cychlorphine’s presence, Williams said.

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