In the past few years, a new threat in the opioid crisis has appeared: a veterinary sedative called xylazine, known on the street as “Tranq” or “Tranq Dope,” which is causing “zombie-like” effects in users.
While this drug is not approved for humans, it is increasingly being mixed with fentanyl, making an extremely deadly drug threat even deadlier.
In this article, I explain what xylazine is, why it is dangerous, and provide an overview of its confirmed presence in Colorado’s drug supply, particularly in Denver.
What Is Xylazine (“Tranq”)?
Xylazine is a non-opioid sedative, pain reliever, and muscle relaxant used exclusively in veterinary medicine for large animals such as horses. It is sometimes known by the brand name Rompun. It is not approved for use with humans due to its potent side effects.
While xylazine is not an opioid (it’s an alpha-2 agonist), it does act as a central nervous system depressant. Dealers add it to fentanyl and heroin to unknowingly prolong the “high” for users (since fentanyl is short-acting) and because it is cheap and easily accessible online, increasing dealer profits. This increases overdose risks since naloxone (Narcan) does not fully reverse it [1].
It usually appears as a white powder or clear liquid, making it difficult to detect by sight or smell. Under the Controlled Substances Act, xylazine is not currently classified as a controlled substance. This makes xylazine potentially easier for drug traffickers to buy than other drugs or drug precursors.
Major Health Risks of Xylazine
Immediate Physiological Effects:
- Profound sedation
- Respiratory depression
- Slow heart rate (bradycardia)
- Dangerously low blood pressure
- Blackouts
The Flesh-Rotting Wound Danger:
- Severe tissue necrosis (irreversible death of body tissue) and skin ulcers, even without injection, often leading to infections and amputations.
Overdose and Naloxone:
- Naloxone (Narcan) does not reverse xylazine’s effects, as it is not an opioid. However, experts still recommend administering naloxone in suspected overdoses in case opioids are also present. Multiple applications may be required.
Is Xylazine in Colorado’s Drug Supply?
In November 2022, the DEA reported the discovery of xylazine-fentanyl mixtures in 48 out of 50 states [2], Colorado among them. Colorado shows an emerging presence in forensic samples but no widespread occurrence of xylazine. State efforts include funding for test strips and surveillance via overdose data.
Denver police detected xylazine through a fentanyl-monitoring project as early as 2022 [3]. As of September 2024, at least four overdose deaths in Colorado have involved xylazine since 2022. All of these were combined with fentanyl or methamphetamine. Health officials continue to monitor for increases but report few cases to date [4].
Denver’s medical examiner reported fentanyl overdoses killed at least 920 people in Colorado in 2022 and 1,087 in 2023, a dramatic rise from previous years. The introduction of xylazine complicates these overdose scenarios.
A 2025 study conducted with the Harm Reduction Action Center (HRAC) in Denver, Colorado, found that 53% of 148 participants had heard of xylazine, and 16.3% reported using it. No participants selected xylazine as their primary drug of choice [5].
Those who selected fentanyl or heroin as their primary drug of choice were significantly more likely to have used xylazine compared to participants whose primary drug of choice was methamphetamine or THC. Of the participants who reported using xylazine or were unsure if they had, 75.7% indicated that their use was unintentional.
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Sources
[1] National Institute on Drug Abuse. 2024. Xylazine.
[2] DEA. 2022. DEA Reports Widespread Threat of Fentanyl Mixed with Xylazine.
[3] Gionet A. 2023. “Tranq” arrives in Boulder County and authorities are concerned about its impact. CBSNews.com
[4] George J. 2024. Has xylazine, a horse tranquilizer used as a drug, caused deaths in Colorado? Coloradosun.com
[5] Yamada M., et al. 2025. Xylazine Usage and Awareness Among People Who Use Drugs in Denver, Colorado. Rocky Vista University, Biomedical Sciences Department, Englewood, CO.