Vancouver police say they suspect the drug fentanyl has contributed to the deaths of three people and an outbreak of non-fatal overdoses in recent days.
Fentanyl is 50 to 100 times more powerful than other opioids and must be carefully monitored to prevent overdose.
Police say two men, aged 24 and 35, and a woman in her 20s died from suspected overdoses between Tuesday night and Wednesday morning.
Seventeen overdoses, mostly on the Downtown Eastside, also occurred between Saturday and Tuesday morning.
Police say Health Canada will analyze drugs recovered from the scenes of the deaths but officers already suspect that fentanyl will be found.
Last last week, police issued a warning after fentanyl was stolen during the robbery of a local pharmacy.
The Canadian Press