Nitazenes Explained: The New Synthetic Opioids Appearing in Colorado

While fentanyl has dominated the opioid crisis, a newer threat, built on an old class of drugs, is emerging in Colorado’s Front Range. Have you heard of nitazenes?

Nitazenes are synthetic opioids that can match or exceed the strength of fentanyl. They were never approved as medicines, and they are now turning up in street drugs and fake pills¹¹. The Colorado Department of Public Health and Environment has recorded nitazene-involved deaths across the Front Range, with at least 13 deaths between August 2021 and October 2023¹.

State and local officials stress that nitazenes show up in powdered opioids and counterfeit tablets. People may think they are buying “just” fentanyl, heroin or pain pills.

In Boulder County, two overdose deaths involved nitazenes. One involved a new nitazene analog (a chemical variant). This shows that the local supply is changing: illicit chemists modify the basic nitazene structure to create new analogs and stay ahead of the DEA.

Nitazenes are still rare compared with fentanyl. But they mark a serious escalation in the opioid crisis because of their extreme potency, their ability to escape detection, and the challenges they pose for first responders and medical examiners. Their presence is expected to grow.

In this article, I explain what nitazenes are, where they have appeared in Colorado, why they are so dangerous, how naloxone works against them, and how to reduce the risk.

What are nitazenes?

Nitazenes, also called benzimidazole-opioids, are a class of synthetic opioids. Some can be up to 500 times (or more) as potent as heroin⁵. They can be made cheaply in illicit labs.

They were first developed in the 1950s for pharmaceutical research, but they were never approved for medical use in the United States or any other country¹¹. Their development stopped largely because of their extreme potency. In recent years they have reappeared in the illicit drug market.

Nitazenes act as full mu-opioid receptor agonists, like heroin and fentanyl. Some analogs, such as N-desethyl isotonitazene and etonitazene, are much more potent than fentanyl.

Nitazene analogs found in overdose cases include^10,11:

• Isotonitazene
• Metonitazene
• Protonitazene
• Etonitazene
• N-pyrrolidino and N-desethyl variants

Small changes to their chemical side chains can sharply change how strong they are. That has led to many different analogs on the street, which makes this deadly drug class very hard to track.

Because they are chemically different from fentanyl and morphine, nitazenes often don’t show up on standard toxicology panels or fentanyl test strips¹⁰.

Nitazene deaths in Colorado

The Colorado Department of Public Health and Environment has reported 13 nitazene-related deaths between August 2021 and October 2023. All happened along the Front Range, from Larimer to El Paso counties^1,2.

Local reports fill in more detail³:

• Denver: five deaths tied to a nitazene compound in 2022 and none in 2023, according to the city’s Office of the Medical Examiner.
• El Paso County: four deaths related to nitazenes since late 2022, according to Coroner Dr. Leon Kelly, as reported in January 2024.
• Boulder County: two deaths since mid-2023.

Testing in the Boulder County cases found a nitazene analog that had never been seen in the U.S. before⁴.

People rarely seek out nitazenes on purpose. They are usually hidden in other drugs, such as counterfeit oxycodone or alprazolam (Xanax) pills, heroin, fentanyl, methamphetamine, cocaine and illicit benzodiazepines^4,11.

Nitazenes across the U.S.

Colorado is not alone. In Tennessee, CDC researchers identified 52 nitazene-involved overdose deaths from 2019 to 2021: none in 2019, 10 in 2020 and 42 in 2021¹⁰. Naloxone was given in only 23% of those deaths, and the authors noted the true count is probably higher because nitazenes are not always tested for¹⁰.

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Something very important to note: in any case when Narcan is administered, 911 is always to be called, even if Narcan is successfully administered and the person does regain consciousness.

Potency and overdose risk

Fentanyl is roughly 50 times more potent than heroin. Animal and lab studies suggest several nitazenes can be 7 to more than 30 times more potent than fentanyl, and etonitazene may be up to 500 times more potent than heroin⁵.

Because these drugs are so strong, the gap between a dose that gets someone high and a dose that kills is frighteningly small.

In practice, studies of overdose patients show severe toxicity, frequent respiratory arrest (stopped breathing) and long-lasting effects for some variants, such as metonitazene and etonitazene⁷. That means a person may need medical monitoring for much longer than after a typical fentanyl overdose.

Why nitazenes are hard to detect

We don’t know the full impact of nitazenes, because they are hard to detect. Standard drug testing panels often miss them¹⁰. The Boulder County Coroner only identified the drug by sending samples to a specialized forensic lab⁴.

A 2026 report from the UK found that nitazenes break down quickly in post-mortem blood samples. That means nitazene deaths may be undercounted by as much as one-third⁶.

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Signs of a nitazene overdose

A nitazene overdose looks like any other opioid overdose. Watch for these signs¹⁴:

Because people often don’t know nitazenes are in their drugs, treat any of these signs as an emergency, even if the person only took a pill they thought was Xanax or Percocet.

Naloxone: does it work on nitazenes?

Yes. Nitazenes are still opioids, and naloxone (Narcan) can reverse nitazene overdoses⁸.

However, nitazene overdoses often need more naloxone than usual.

In a review of nitazene overdose cases, the median total naloxone dose was 3 mg for isotonitazene and etonitazene and 6 mg for metonitazene. Many patients were hospitalized, with average stays of about 360 hours for metonitazene⁷.

In an emergency department study, patients with nitazene and other novel opioid overdoses received more naloxone doses in hospital than patients who had taken fentanyl alone⁹.

Giving more than one dose of naloxone is safe¹⁰.

Harm reduction recommendations

For people who use drugs, frontline workers and clinicians in Colorado:

• Expect contamination: Assume that any opioid powder or pill bought outside a pharmacy may contain nitazenes, even if it was sold as fentanyl, heroin or oxycodone. Colorado public health officials stress that in an unregulated market, you can never be sure what is in a substance.
• Test and use more safely: Fentanyl test strips help, but they don’t detect all nitazenes. Look for nitazene-capable drug checking where it exists. Don’t use alone, start with a very small amount, and avoid mixing with alcohol, benzodiazepines or other depressants⁸.
• Plan for higher naloxone needs: Carry more than one dose. In clinical settings, be ready for repeat dosing, airway support and longer monitoring after reversal⁹.
• Connect people to opioid treatment: Because nitazenes are so potent, fast access to medications for opioid use disorder, such as buprenorphine, methadone and naltrexone, matters more than ever¹³. Emergency departments and outreach programs should link people to care.
• Know the law: The DEA has placed many nitazenes in Schedule I and has used emergency scheduling for newer analogs, but chemists keep creating new variants to stay ahead of the law¹¹.

Why treatment matters more than ever

Every time someone uses street opioids, they are gambling on what is inside. The supply changes faster than tests, laws and warnings can keep up. The safest way to avoid nitazenes is to stop using illicit opioids, and that is much easier with support.

Stopping opioids suddenly causes withdrawal, with muscle aches, sweating, diarrhea, anxiety and trouble sleeping¹². Most opioid overdose deaths happen in people who have just detoxed, because their tolerance has dropped¹². That is why medical detox, medication and ongoing care work best together.

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Substance use disorder, or addiction, can feel overwhelming, but Red Rock Recovery Center can help you begin your recovery today, guided by our core values of community, connection and purpose and a trauma-informed approach.

Red Rock offers a full continuum of care for substance use disorder, including opioid and alcohol addiction. Care runs from medical detox through residential treatment, PHP, IOP and sober living, plus aftercare. Medical detox usually takes 7 to 10 days, with nursing around the clock.

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