Health officials across the United States are raising alarms about a dangerous new substance appearing in the illegal drug supply.

The drug, commonly called “rhino tranq,” is medetomidine, a veterinary sedative that is now being detected alongside fentanyl in multiple regions.

Authorities warn that the combination creates a highly unpredictable and potentially fatal risk, particularly because the sedative component complicates both overdose response and withdrawal management.

The Centers for Disease Control and Prevention and the White House Office of National Drug Control Policy issued a formal advisory after identifying increasing evidence that medetomidine is spreading within illicit drugs.

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Surveillance data, including forensic testing and wastewater monitoring, show that the substance is becoming more common and often appears in combination with fentanyl.

According to officials, this pattern raises concerns because the two substances together can intensify sedation and increase the likelihood of respiratory depression.

Medetomidine, also known as “rhino tranq,” “mede” or “dex,” is described as a veterinary sedative that causes prolonged sedation and affects the nervous system. It is not approved for human use.

Experts warn that the drug’s presence in the illegal supply introduces additional complications beyond what clinicians typically encounter with opioid overdoses.

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Dr. Adam Scioli, chief medical officer of Caron Treatment Centers in Pennsylvania, called the trend a “concerning and rapidly evolving development” in the illicit opioid supply.

One of the most troubling aspects is how frequently medetomidine appears alongside fentanyl. Forensic reports show that roughly 98 percent of samples containing the sedative also included fentanyl, which significantly increases danger because both substances depress breathing and consciousness. Officials note that the sedative can cause deep sedation, slow heart rate, low blood pressure and respiratory depression, especially when combined with opioids.

The spread has been rapid. Data cited in the advisory indicate that detections rose sharply over recent years. In 2023 there were 247 incidents of medetomidine in drug samples, followed by 2,616 in 2024 and 8,233 in 2025.

That surge represents more than a 3,000 percent increase. At the same time, the drug has been identified in at least 18 states and Washington, D.C., with concentrations reported in the Northeast and Midwest.

Officials emphasize that the risks extend beyond overdose itself. Withdrawal symptoms from medetomidine can begin within hours and may escalate quickly. Symptoms include rising blood pressure, agitation, nausea and altered mental status.

Severe cases may lead to cardiac or neurological complications that require intensive care monitoring. “Management may require ICU level monitoring and care,” Scioli said, underscoring the seriousness of the condition.

Another complication involves treatment. Naloxone, commonly known as Narcan, remains essential for reversing opioid overdoses, yet it does not counteract the sedative effects of medetomidine.

Experts caution that while naloxone should still be administered because fentanyl is often involved, it may not fully restore consciousness. This limitation increases uncertainty for first responders and medical professionals attempting to stabilize patients.

Public health officials point to real world consequences. A cluster of overdoses in Chicago linked to medetomidine involved more than 175 cases, with at least 16 hospitalizations and one death.

Such events demonstrate how quickly a new drug combination can strain emergency services and complicate care.

The emergence of “rhino tranq” also reflects a broader trend within the illicit drug market. As enforcement and awareness increase around existing substances, suppliers often introduce new compounds to maintain potency or avoid detection.

Medetomidine is not routinely identified on standard toxicology screens, which increases the risk that clinicians may initially miss its presence. “Medetomidine is not routinely detected on standard toxicology screens,” Scioli warned, adding that this creates a higher risk of under recognition.

Officials stress that vigilance is essential. The combination of fentanyl and medetomidine creates a scenario where overdoses may present differently and require more intensive care. Because of this, clinicians, first responders and public health agencies are being urged to monitor trends closely and adjust response protocols accordingly.

The warning arrives at a time when the United States continues to confront an ongoing opioid crisis. While some progress has been made in awareness and treatment, the introduction of new substances complicates those efforts.

Medetomidine’s rise serves as a reminder that the illicit drug market evolves quickly and that public health responses must adapt just as rapidly.

Authorities are encouraging continued education, expanded testing and coordinated response strategies. At the same time, experts emphasize that prevention and treatment remain critical components of addressing substance abuse.

The spread of “rhino tranq” illustrates how dangerous drug combinations can emerge and spread quickly, therefore requiring swift action from health professionals and policymakers alike.