North America’s only supervised injection site for drugs like cocaine, speed and crystal meth has found that 90% of its clients’ heroin contained the powerful synthetic fentanyl.

Vancouver’s Insite, which offers health services including supervised injection, said that of the 173 drug checks it did for fentanyl in a month, 90% tested positive for the potent synthetic drug.

Fentanyl, which is about 30 to 50 times more powerful than heroin, has caught the attention of medical and law enforcement authorities across North America as it becomes connected to more and more deadly overdoses in the opioid epidemic.

“This is happening all over, other cities may not have the same degree of contamination we have here in Vancouver, but it’s coming,” said Mark Lysyshyn, medical health officer with Vancouver Coastal Health, which operates Insite.

This past week in the US, a spate of overdoses broke out in several cities, including Cincinnati, where officials suspect fentanyl is behind 78 overdoses in two days.

Insite checked for fentanyl as part of a pilot program that lets clients test their drugs at an injection station with strips that were developed to check urine for fentanyl.

The program was inspired by a similar service offered at some music festivals for people who want to test the purity of ecstasy – and by client demand. “They’ve seen people overdose and die, so they are very aware of it and they are looking for ways to stay safe,” Lysyshyn said.

Lysyshyn cautioned that the findings were biased toward people who suspected they had contaminated drugs and that the results were not meant to show the overall contamination of fentanyl in Vancouver or anywhere else. He said it does, however, show the increasing threat of fentanyl, which is smuggled, usually from China, in small, but highly potent, amounts that are a smart economic choice for drug dealers.

“The purpose of an intervention like this is to give users information so they can change their behavior,” Lysyshyn said.

The testing occurred from 7 July to 3 August, and will continue for a few months before health workers re-evaluate it to see whether it is helping their clients.

The strip does not check for other substances, but it can be used to check drugs like cocaine, crack, speed and crystal meth. Clients did checks for these drugs significantly less and the results were less likely to be positive.

Insite introduced the program after a sharp increase in the amount of overdoses at the facility from 132 in January to July of 2006 to 573 in the same period of 2016.

Insite opened in 2003 and remains the only supervised injection facility in North America, with more than 6,500 people visiting in 2015. Overdose deaths declined by 35% near Insite while the rate dropped 9% in all of Vancouver, according to a 2011 study in The Lancet.

But the push to introduce the controversial practice of supervised injection outside of Vancouver has grown amid the latest wave of opioid addiction, which the Centers for Disease Control and Prevention said causes 78 fatal overdoses a day in the US.

In February, the mayor of Ithaca, New York, proposed opening a similar facility as Insite, though that is technically illegal under federal law – and controversial.

“In the US, traditionally, we’ve looked at heroin as just a very, bad evil thing so supervised injection facilities is seen as a way of being complicit with people using those drugs,” said Marion Riedel, an associate professor of professional practice at the Columbia School of Social Work.

Supervised injection is one of many interventions touted in the harm reduction model for treating drug addiction, which seeks to reduce the negative consequences of drug use. The model also endorses programs like syringe-exchanges and medication-assisted treatment.

Harm reduction has long been controversial in the US, but the latest wave of opioid addiction has led to softening of laws in places like Kentucky, which made needle-exchanges illegal after an HIV outbreak among injection drug users in nearby Indiana.

Riedel said that drug addiction is not a new problem in the US, these softening attitudes could change treatment options in the US: “When we really believe it’s going to be white middle class people who got addicted because they got addicted on opiates from their doctors, it’s going to be a game changer – but we’re not there yet.”