‘Silent epidemic': Study warns of deadly drug mix on the streets

CTV News

16-07-2025

A growing number of overdose deaths in North America involve a dangerous combination of opioids and stimulants, a trend that researchers in a new study are calling a 'silent epidemic.'
Led by the University of Alberta, the study warns that while public attention remains focused on opioids like fentanyl and heroin, stimulant use is increasing each year, playing a far greater role in overdose fatalities across Canada and the United States.
'This is actually a North American thing,' said Bo Cao, lead author of the study and associate professor of psychiatry at the University of Alberta, in a video interview with CTVNews.ca. 'If you take a look at other developed countries, for example, the U.K., Australia, and other parts of Europe, you actually don't see this alarming increase every year for opioid related deaths.'
The study analyzed overdose death data from the National Institute on Drug Abuse (NIDA) in the U.S. between 1999 and 2021, as well as trends from the Public Health Agency of Canada and the Alberta Substance Use Surveillance System, including opioid use between 2016 and 2022 and stimulant use between 2018 and 2022.
The researchers found that people who use both opioids and stimulants, sometimes intentionally and sometimes unknowingly due to contaminated street drugs, are at a higher risk of overdose.
'If the drug is contaminated, I don't think we currently have a very good way to check it,' said Cao. 'Sometimes people think they're using stimulants, but if there is some contamination and they are also not tolerant to high-potency opioids, they overdose unconsciously.'
What's in the mix?
Opioids are a class of drugs used primarily to treat pain. They include both prescription medications like morphine and oxycodone, as well as powerful street drugs such as heroin and fentanyl.
'Opioid is usually a strong painkiller medically, but it's actually used for other purposes,' said Cao. 'The most famous ones are morphine and fentanyl.'
Many of today's most dangerous opioids, including fentanyl, are synthetic, meaning they are made in a lab rather than derived from the opium poppy.
Stimulants, on the other hand, are substances that increase alertness, energy and attention. Some, like those used to treat ADHD, are legal and medically prescribed. But illicit stimulants, such as methamphetamine and cocaine, are commonly used recreationally and are often found in the unregulated drug supply.
Three waves of opioid crisis
Researchers say the opioid crisis in North America has unfolded in three distinct waves. The first was fuelled by prescription painkillers, the second by heroin, and the third, still ongoing, by the widespread availability of powerful synthetic opioids, such as fentanyl.
But the current wave, they argue, is increasingly defined by the co-use of opioids and stimulants.
In 2021 alone, more than 80,000 opioid-related deaths were reported in the United States, and nearly 8,000 in Canada. Many of those involved stimulants.
'Once you look at the deaths that involved both opioid and stimulants, you actually see they are increasing at an even higher speed compared to the opioid-related deaths,' Cao said.
A crisis the public isn't seeing
Researchers also used Google Trends to gauge public awareness and found that, while searches for opioids remain relatively high, public interest in stimulants has dropped sharply since the mid-2000s, despite an alarming rise in deaths involving both types of substances.
'There is a trend, and it's quite clear that the public is not picking this up,' said Cao. 'Maybe only the ones who get access to these drugs or who actually help those people cope with these problems ... they probably know better.'
The gap in awareness could have real-world consequences, the study warns, since public perception often shapes how policies are made and where funding is directed.
Stimulants like methamphetamine and cocaine are often used in combination with opioids in a mix known as a 'speedball,' a term well-known on the street, says Guy Felicella, a harm reduction and recovery advocate in British Columbia.
'The combination together is that they usually enhance each other's highs,' he said in a video interview with CTVNews.ca. 'The calming effect or the come-down from the fentanyl can level off the stimulant as well.'
While people have been mixing opioids and stimulants for years, Felicella says today's unpredictable street drug supply is more dangerous than ever.
'What's predominantly killing people on the street is not the stimulants — unless they're tainted with fentanyl,' he said. 'If you are a stimulant user only, and you're buying cocaine and it does contain fentanyl, then you are at extreme risk for death.'
Turning data into action
To better understand and prevent overdose deaths, Cao and his team have also developed a machine-learning model that can predict an individual's risk of overdose using population-level health data.
Researchers say their study, recently published in the journal Nature, could help policymakers identify high-risk individuals or communities, target interventions more effectively and allocate resources with greater precision.
For Cao, the next step is clear: apply the science responsibly, collaborate across sectors and bring affected communities into the conversation.
'If we have such tools, such insights from the data, how can we make them more useful to clinicians, to patients, to families and caregivers?' he said, adding that requires real engagement, not just research.