Animal tranquilizers are increasingly contaminating Toronto’s fentanyl supply
Medetomidine and other veterinary tranquilizers are showing up more often in expected fentanyl samples, deepening the unpredictability and harms of Toronto’s unregulated drug supply.
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By Torontoer Staff
Animal tranquilizers are appearing more frequently in Toronto’s unregulated fentanyl supply, changing the risks faced by people who use drugs and complicating clinical response. Toronto’s Drug Checking Service and hospital clinicians report a rapid rise in medetomidine, a long‑acting veterinary sedative, alongside the already present xylazine.
The presence of these substances matters because they are not approved for human use, can cause profound sedation, and cannot be reversed with naloxone, the opioid antidote. Toronto has recorded just under 4,000 opioid toxicity deaths from 2015 through the end of 2024.
What medetomidine is and why it is showing up
Medetomidine is a veterinary surgical anaesthetic and sedative used in animals. It produces deep, prolonged sedation, lowers blood pressure and heart rate, and can slow breathing. When combined with potent opioids, benzodiazepine‑related drugs, or other animal tranquilizers such as xylazine, the risk of life‑threatening respiratory depression and organ injury increases.
The fentanyl supply is contaminated. That’s what’s really driving this crisis.
Karen McDonald, executive director, Toronto Drug Checking Service
Toronto’s Drug Checking Service first detected medetomidine in the city’s supply in December 2023. The substance became more common in the fall of 2024. By February 2025 medetomidine was found in about 25 per cent of expected fentanyl samples, and TDCS has since reported it in a much larger share of tested samples.
How the drug supply has changed
Earlier in the city’s drug‑checking era, benzodiazepines were the most frequent non‑opioid contaminants in expected fentanyl. These prescription drugs carry risks, but because they are approved for human use their effects were somewhat more predictable. Xylazine, often called tranq or horse tranquilizer, emerged in Toronto in September 2020 and was consistently detected in about 10 per cent of expected fentanyl samples until more recent shifts.
Public health researchers link these shifts to changing access to precursor chemicals and supply chain dynamics. When certain precursors become regulated, suppliers pivot to new compounds. That process increases instability in the unregulated market and can introduce substances with unfamiliar or more hazardous effects.
We’re playing a continuous game of Whack‑A‑Mole. It’s dangerous for overdoses.
Gillian Kolla, public health researcher, Memorial University
Clinical challenges for emergency care
Emergency departments treat substance‑related emergencies by stabilizing breathing, circulation and consciousness, and by administering naloxone when opioid overdose is suspected. When patients have low blood pressure and heart rate despite naloxone, clinicians suspect additional depressant agents. That complicates triage and treatment and can require intensive supportive care.
Different drugs affect the body differently.
Dr. Sunil Gupta, emergency physician, St. Michael’s Hospital
Because medetomidine and xylazine are not opioids, naloxone will not reverse their sedative effects. Prolonged respiratory suppression or low blood pressure can cause organ damage even when a person survives the initial event. Clinicians say the unpredictability of the supply turns treatment into a guessing game and increases the likelihood of poor outcomes.
Harm reduction, monitoring and policy implications
Frontline harm reduction workers and drug‑checking services have tried to keep pace by sharing timely alerts and testing results. Community organisations provide education, safer‑use information, and referrals, even as supervised consumption sites in some areas have closed, reducing options for supervised use.
Our goal is to try to be as timely as possible with the ever‑changing supply. It’s about being able to provide information to people, so they make an informed choice about their drug use.
Gab Laurence, director of harm reduction, Parkdale Queen West Community Health Centre
- Expand and support drug‑checking services to track contaminants in real time
- Maintain or restore supervised consumption sites to reduce harms and connect people to care
- Share timely warnings and test results with people who use drugs and frontline services
- Advance policies toward a regulated, pharmaceutical supply to reduce contamination and unpredictability
Researchers and clinicians say data from services like Toronto’s Drug Checking Service are essential to understanding changes in the market and informing clinical and community responses. They also stress that policy choices, including funding for supervised consumption and harm reduction, shape the vulnerability of people who use drugs.
What this means for risk and prevention
The increasing presence of medetomidine and other non‑opioid tranquilizers in expected fentanyl samples makes the supply more unpredictable and more dangerous. People who use drugs and the services that support them face greater uncertainty about effects, treatment options and outcomes. TDCS and frontline clinicians continue to monitor trends and share findings to reduce harm.
The longer term response advocated by public health experts is a regulated supply, paired with expanded harm reduction and clinical capacity, so that the harms from contaminated unregulated drugs can be reduced.
fentanylharm-reductiondrug-supplymedetomidinexylazineTorontopublic-health
