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Health and government officials are warning of a potential deadly substance in the illegal drug supply.

The Centers for Disease Control and Prevention (CDC) and the White House Office of National Drug Control Policy (ONDCP) issued a health advisory on Thursday about reports of medetomidine being detected in fentanyl.

Also known as “rhino tranq,” “mede” or “dex,” medetomidine is a veterinary sedative that causes severe, prolonged sedation. Classified as an alpha-2 agonist, it acts on the nervous system similar to other veterinary sedatives, like xylazine, and can cause life-threatening withdrawal symptoms.

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The advisory is based on surveillance data, including forensic drug testing, wastewater analysis, clinical case reports and overdose investigations.

In 2023, there were 247 incidences of medetomidine detected in drug samples, which rose to 2,616 in 2024 and 8,233 in 2025 – a more than 3,000% increase. Forensic drug reports showed that about 98% of medetomidine-positive samples also contained fentanyl. 

The drug has been detected in at least 18 states and Washington, D.C., with a concentration in the Northeast and Midwest regions of the U.S., per the CDC alert.

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

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“Its co‑occurrence with fentanyl significantly complicates overdose presentation and withdrawal management, further increasing both clinical acuity and unpredictability,” he told Fox News Digital.

“Medetomidine is not routinely detected on standard toxicology screens, increasing the risk of under‑recognition without a high index of clinical suspicion.”

Naloxone (Narcan), known for its overdose reversal effects, does not counteract medetomidine, the advisory warned.

“While naloxone remains essential for reversing opioid‑induced respiratory depression, it does not address the sedative effects of medetomidine,” Scioli confirmed.

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The initial effects of the drug include deep sedation or decreased consciousness, bradycardia (slow heart rate), hypotension (low blood pressure) and respiratory depression, especially when combined with fentanyl and other opioids.

Withdrawal symptoms typically begin about a few hours after taking medetomidine. They can be severe and rapid, peaking at about 18-36 hours, according to experts.

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Initial withdrawal symptoms include rising blood pressure, tachycardia, agitation and nausea/vomiting, gradually leading to severe hypertension, altered mental status, and possible cardiac or neurologic complications, per the alert.

Severe cases require intensive care in a hospital. “Management may require ICU‑level monitoring and care,” said Scioli.

In a May 2024 example cited by the CDC, medetomidine in the illegal opioid supply was linked to a cluster of overdoses in Chicago, potentially exceeding 175. At least 16 people were hospitalized and one died.

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There were some limitations to the surveillance, the agency acknowledged. Surveillance systems rely on small samples that may not be representative of all areas.

There is also the chance that the numbers could be overestimated due to contamination or repeated use of drug paraphernalia. Conversely, numbers could actually be higher than recorded, as medetomidine is rapidly metabolized in the body and is not typically tested in clinical settings.

The surveillance was conducted by the CDC with support from federal public health programs and collaboration with other agencies.

Scioli noted that the alert highlights the need for “careful assessment beyond standard opioid toxicity models,” as well as close coordination with toxicology, emergency medicine and public health partners.

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“The drug supply is evolving in ways that strain traditional opioid‑focused frameworks and demand greater clinical vigilance,” he said.

“From a treatment perspective, this is another clear example of why addiction care must be adaptive, medically sophisticated, and grounded in whole‑person, long‑term recovery — not solely acute stabilization,” he added.

A panel of judges has ruled that it is impossible to determine which of two identical twins fathered a woman’s baby.

The child (referred to as “P”), who was conceived in 2017, is now 8 years old, according to court documents.

The U.K. woman, who was only identified as “the mother,” reportedly engaged in sexual relations with the identical twins just four days apart.

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She remained in a relationship with one twin, who was named on the birth certificate and initially acted as the legal father, the filing stated. When the relationship ended, it triggered a legal dispute.

The mother and the twin who is not listed on the birth certificate brought the case, seeking to overturn an earlier ruling and have him legally recognized as the child’s father, the document detailed.

The Court of Appeals ruled that legal paternity rights are only granted to a genetic father. While DNA testing shows a 50/50 chance for each twin to be the father, there is no definitive answer.

“Currently, the truth of P’s paternity is that their father is one or other of these two identical twins, but it is not possible to say which,” stated Lord Justice Moylan in the Court of Appeal ruling.

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Moylan added that the child’s paternity “is binary and not a single man,” highlighting the legal uncertainty created by the case.

Since neither twin can prove he is the biological father, neither can be given legal parental responsibility, the court declared.

The case is significant because it ​​reveals a limit of DNA evidence, which is the foundation of many legal cases.

“Identical twins share the same genetic DNA code. While, over time, there are subtle changes to patterns around the DNA that would allow matching in some circumstances for adults’ cells, these markers are significantly degraded at the time of fertilization — making it not practical with current technology to assign paternity to identical twin brothers,” Paul Brezina, physician and fertility expert at Fertility Associates of Memphis, an Ivy Fertility Center, told Fox News Digital.

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In addition to medical questions, this situation could have an emotional impact on the parents and child, noted Brezina, who was not involved in the case.

“Support for the patient and the child through counseling and their medical professionals is vital moving forward,” he advised. 

Identical twins have long presented a challenge in DNA testing, previous medical research has shown. 

Monozygotic (identical) twins share virtually identical genetic profiles, including the markers used in standard paternity tests, meaning they “cannot be differentiated using standard DNA testing,” according to a study published in Forensic Science International: Genetics.

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There are more advanced methods, such as whole genome sequencing, that can detect some rare genetic mutations among twins, but researchers say these techniques are complex, expensive and not commonly used in legal cases.

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A study published in PLOS Genetics confirms that distinguishing between identical twins’ DNA requires highly specialized analysis that goes beyond standard forensic testing.