Animal Tranquilizer Contributes to Fatal Overdoses in Philadelphia

Phili ambulance

A story out of Philadelphia, Pennsylvania, made national news partly for its sad nature and partly for the deeper meaning behind the story. According to the Philadelphia Department of Public Health, a tranquilizer drug called xylazine (approved only for veterinary use) was involved in nearly one-third of Philadelphia’s heroin and fentanyl deaths in 2019.

What exactly happened in Philadelphia, what danger is there in human consumption of xylazine, and why is this local case actually a national, even an international, issue?

Reporting on Concerning Drug Use in Philadelphia

In a February 2021 issue of Injury Prevention, lead study author Jewell Johnson (an epidemiologist with the Philadelphia Department of Public Health) presented toxicology reports for fatal overdoses in Philadelphia from 2010 to 2019. According to the data, the animal tranquilizer xylazine (called "tranq" on the streets) was present in almost 33% of fatal overdoses in Philadelphia in 2019.

It is concerning enough that an animal tranquilizer is being mixed into heroin and fentanyl. And to make matters worse, the 2019 numbers represented a stark increase in the presence of the tranquilizer in the Philadelphia drug supply. For example, from 2010 to 2015, xylazine was present in just 2% of overdoses. In 2016, it was present in 10% of overdoses. In 2018 it was present in 18% of overdoses. If action is not taken to curb xylazine misuse, the drug will continue to crop up in toxicology reports and likely in greater numbers.

Xylazine Risk, Defined

In October 2020, the Frederic Rieders Family Foundation released a public health warning regarding xylazine. The report laid out in detail the public health risk posed by mixing xylazine with opioids. The report also mapped out potential citywide public health responses, as well as emergency medical response techniques to administer to addicts who overdosed on xylazine.

According to the report, xylazine poisoning can cause bradycardia, (abnormally slow heart action), severe respiratory and central nervous system depression, hypotension, and other adverse changes in cardiac function. Furthermore, when addicts use xylazine with heroin, fentanyl, or cocaine, it can have an additive effect, amplifying the negative effects of the drugs. Most importantly, adding xylazine to opioids increases the risk of overdose and death.

Why xylazine? According to research and survey data, when xylazine is added to fentanyl, it increases the potency and duration of a fentanyl high. As seeking a more potent, prolonged high is simply part of the nature of addiction, it’s not surprising that addicts would seek out fentanyl or heroin that had been mixed with xylazine.

However, mixing xylazine with opioids increases risk. The two drugs combined depress both blood pressure and the central nervous system. That has the combined effect of slowing breathing and heart rate, which results in a high risk of overdose and death.

A Similar Story Out of Puerto Rico

Overdose rescue
Photo by Tyler Olson/

While one would hope that xylazine abuse in Philadelphia is an isolated case of drug abuse that a focused public health response could resolve, Philadelphia is not the first location where addicts have begun to mix xylazine with opioids. Since the early-2000s, veterinary drugs, xylazine included, have gained popularity as recreational drugs in urban areas all across the country and world.

For example, xylazine misuse cropped up in Puerto Rico about a decade ago, an epidemic of abuse that left hundreds of Puerto Ricans addicted and several dead from overdoses. Furthermore, Puerto Ricans who mixed xylazine with other drugs like opioids or cocaine often experienced other severe health outcomes like skin lesions and nonfatal overdoses.

Drug “Cocktails”—Taking a Look at the Danger of Mixing Drugs

Unfortunately, the issue of xylazine misuse in Philadelphia is not an isolated case. As clandestine drug manufacturing technologies advance and as addicts continuously look for different, stronger, and longer-lasting highs, mixing drugs has become more common.

But here are some reasons why mixing drugs creates even more risk for addicts:

  • Addicts often end up taking a drug without knowing what’s in it. This is an obvious risk. Addicts rarely have a definitive way of determining what is in the drugs they take, and drug dealers are not reliable sources of information.
  • Drug dealers’ main concerns are about profit, not product integrity. People who manufacture and sell illicit drugs will often mix fillers and other chemical additives into drugs to increase supply, maximize profit, and boost potency (making the drugs more addictive and leading to return customers).
  • When drugs are mixed together, they can cause dangerous physiological reactions in the body. A single drug by itself will have its own list of potential, harmful side effects. But combining drugs is even more hazardous, as drugs can react differently when in the body and in the presence of other drugs. This can lead to unpredictable, even fatal effects.

Opioid Addiction—Clear Danger Exacerbated When Other Drugs are Mixed In

It is extremely dangerous to misuse opioid drugs. According to the National Institute on Drug Abuse, of the more than 70,000 Americans who died from drug overdoses in 2019, more than two-thirds of those deaths (49,860 deaths) were directly attributable to opioids. Synthetic opioids like fentanyl caused about 36,359 deaths. Prescription opioids caused another 14,139 deaths, and 14,019 deaths were caused by heroin.

More Americans die from opioids than the deaths that occur from all other drugs combined. And when non-opioid drugs are mixed in with opioids (like xylazine), risk factors increase, and addicts are more likely to lose their lives.

Why It’s So Important That Drug Addicts Get Help

Mother consoling daughter

Fatal drug overdoses are now the leading cause of accidental deaths for Americans under the age of 50. That means more Americans are dying from drug overdoses than firearms, car accidents, homicides, or HIV/AIDS. According to the National Institute on Drug Abuse, while fewer than 18,000 people died from drug overdoses in the United States in 1999, more than 70,000 died from such overdoses in 2019, a more than 200% increase.

Drug addiction is not a new problem. And drug-related deaths are not new either. What is new is the sheer number of deaths occurring each year and the fact that the annual death toll has skyrocketed since the turn of the century. Drug addiction looks very different in 2021 than it did in the late-1990s. Drug addiction is far more likely to be fatal now.

Because of the risk of death alone (and there are many other, nonfatal risk factors), addicts should do everything they can to get help as soon as possible. Addiction is often fatal, but it does not have to be. Help for drug and alcohol addiction does exist and is available to addicts.


Reviewed by Claire Pinelli, ICAADC, CCS, LADC, RAS, MCAP, LCDC-I



After working in addiction treatment for several years, Ren now travels the country, studying drug trends and writing about addiction in our society. Ren is focused on using his skill as an author and counselor to promote recovery and effective solutions to the drug crisis. Connect with Ren on LinkedIn.