Medetomidine, a powerful new “zombie drug” known as “rhino tranq,” has reached California.

The California Department of Public Health (CDPH) stated in an email to The Epoch Times that the agency is aware of four medetomidine-related overdose deaths in 2025, an agency spokesperson said. She noted that the data is preliminary and more cases could be identified.

“The four medetomidine-related overdose deaths were associated with fentanyl, however CDPH does not have data on the extent to which medetomidine may be mixed with fentanyl in the drug supply,” the spokesperson said.

No overdose deaths linked to medetomidine were reported in the state during prior years, according to the department.

Jacqui Berlinn, co-founder of San-Francisco-based Mothers Against Drug Addictions and Deaths (MADAAD), told The Epoch Times in a text that she is horrified by the inhumanity of introducing an even more potent veterinary tranquilizer to fentanyl without regard for the lives of people struggling with addiction.

“This is what keeps mothers awake at night. There is a special cruelty in adding a drug like medetomidine to fentanyl,” she said. “As a mother who understands addiction, I see this for what it is: an escalation that shows complete disregard for human suffering and human life. I am horrified by the cruelty behind adding an even more powerful drug to an already dangerous supply. This isn’t accidental. It’s reckless disregard for human life.”

Medetomidine, first found in Philadelphia’s drug supply in May 2024, is 100 to 200 times more potent than xylazine—known as “tranq”—and can cause longer-lasting sedation, low heart rates, and more severe withdrawal symptoms. It is not an opioid but is found in the street opioid supply, according to the Philadelphia Department of Public Health (PDPH).

Medetomidine, like xylazine, is called a “zombie drug,” which describes the behavior of users experiencing its heavy sedative effects. Both medetomidine and xylazine are animal tranquilizers not meant for human use, according to CDPH.

Concurrent use of fentanyl and veterinary tranquilizers is associated with severe and necrotic skin and soft tissue injuries, which complicate treatment.

Xylazine was first found in illicit street drugs in Philadelphia in 2006, and by 2023 was detected in nearly all fentanyl tested by PDPH. But since the increase of medetomidine, there has been a corresponding decrease in the prevalence of xylazine in Philadelphia’s drug supply.

In December 2024, PDPH released a health alert notifying providers of severe withdrawal symptoms requiring intensive care unit level of care attributed to concurrent use of medetomidine and fentanyl.

In May 2025, the CDC reported that 165 patients were admitted to Philadelphia’s health systems between Sept. 1, 2024, and Jan. 31, 2025, with a newly recognized medetomidine withdrawal syndrome. Of those patients, 91 percent were admitted to an intensive care unit, and 24 percent were intubated, according to PDPH.

As medetomidine replaces xylazine, an increase in the variation and severity of withdrawal symptoms has led to more emergency department visits reported, with a decrease in the number of patients seeking treatment for xylazine-associated wounds and presence of xylazine in Philadelphia’s drug supply, according to PDPH.

From May to November 2024, the percentage of Philadelphia illicit drug samples with medetomidine increased from 29 percent to 87 percent, while the percentage of samples with xylazine decreased from 97 percent to 42 percent, suggesting that medetomidine is quickly overtaking xylazine, PDPH stated.

During this period, medetomidine was also found in overdose death data from the PDPH Medical Examiner’s Office and, like xylazine, was always found in combination with fentanyl.

Aside from heavy sedation, medetomidine can cause low blood pressure, slow heart rate, dizziness, extreme tiredness, shortness of breath, nausea, blurred vision, and confusion, according to the PDPH Substance Use Prevention and Harm Reduction (SUPHR) division.

CDPH warned that naloxone, also known by the brand name Narcan, won’t reverse the direct effects of medetomidine toxicity. But because medetomidine is often mixed with fentanyl or other opioids, “administering naloxone is recommended” to counteract the effects of opioids that could present for any suspected overdoses, the agency stated.

Medetomidine withdrawal can be severe and may require immediate emergency treatment, so “prompt medical attention is critical,” CDPH said.

The effects of medetomidine can include sedation, analgesia, muscle relaxation, anxiolysis, bradycardia, hypotension, hyperglycemia, and hallucinations, according to CDPH.

PDPH advised that someone overdosing from a drug containing medetomidine may stay sedated and nonresponsive after receiving naloxone, so when reversing an overdose, it’s important to focus on the person’s breathing rather than their responsiveness, ensuring that the person takes at least one breath every five seconds and is not pale, gray, or blue, and monitoring them until emergency help arrives.

Those experiencing withdrawal are advised to call 911 immediately, the CDPH agency spokesperson said.

The Substance Use Disorder Referral Line in California is 800-879-2772 (toll-free). Outside California, it’s (916) 327-3728, and additional information on California treatment locations can be found at Choose Change California.

The Treatment Atlas, a free and confidential resource to find and compare treatment and detox programs, is also available.