A pilot project that allows Vancouver drug users to test substances for the deadly opioid fentanyl is being expanded in an effort to reduce overdose deaths.

Vancouver Coastal Health says the pilot project found that clients who found fentanyl in their drugs were 10 times more likely to reduce their dose and, as a result, they were 25 per cent less likely to overdose.

The initiative launched at Insite, a supervised drug-use site, in July, 2016, in response to the crisis that has killed hundreds of people in the province.

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To date, more than 1,400 tests have been conducted.

The health authority says 80 per cent of all drugs tested were positive for fentanyl, including 84 per cent of heroin samples and 65 per cent of non-opiate drugs, such as crystal meth, ecstasy and cocaine.

The check involves dipping a test strip into a drug sample that has been diluted with a few drops of water, revealing a positive or negative result within seconds.

The free drug-checking service will now be available at any of the city's four overdose-prevention sites and the Powell Street Getaway safe-injection site.

Judy Darcy, British Columbia's Minister of Mental Health and Addictions, said the drug test empowers users to make informed decisions about whether or how much they consume.

"At the provincial level, we are actively looking at how we might roll out such drug-checking services more broadly. The information being gathered by Vancouver Coastal Health with this project will be invaluable to this work," she said in a news release.