There have been seven overdoses in the Fraser Valley community located east of Vancouver since May, said a statement issued by Const. Ian MacDonald on Wednesday morning.
"Our frontline officers have spoke with many individuals who have reported being concerned about the potency of heroin that is currently being bought, sold and sued," said MacDonald.
"A possible explanation for the increased potency and the overdose may be the presence of fentanyl in the drugs."
Police have yet to confirm there is fentanyl in the drugs being sold in the area, but they have sent a sample for testing.
"However, given the potential health risks we cannot wait for the results before issuing this warning. Users of illicit drugs, particularly heroin, must exercise extreme caution and call 911 with any signs of medical distress."
The warning comes the day after the B.C. Coroners Service confirmed toxicology tests showed Glee actor Cory Monteith died of a toxic mix of heroin and alcohol in a Vancouver hotel room early Saturday morning.
But the coroner did not say anything to indicate that Monteith's deaths was linked to fentanyl or overly potent heroin.
In May, the B.C. Provincial Health Officer issued a similar warning that there had been a spike in overdoses linked to fentanyl.
During the first four months of 2013, 23 deaths were linked to fentanyl in B.C. and a large supply of the drug had been seized by Vancouver police.