On the heels of hundreds of overdose deaths related to fentanyl, authorities are now warning the public about a new and extremely lethal drug that's hit the streets in Western Canada.

W-18 is a synthetic opioid 10,000 more potent than morphine and 100 times more potent than fentanyl.

Late last month, police in Calgary put out a warning after tests found W-18 in three pills seized in a drug bust.

'There's more out there'

"I can guarantee you there's got to be more out there," said Sgt. Jason Walker. "We just haven't seen it yet."

Dr. Evan Wood, Vancouver Coastal Health director for addiction services, says the fact that just three pills containing W-18 were discovered is "interesting."

Dr. Evan Wood

Dr. Evan Wood says W-18 is so powerful, it's likely of limited use in an illicit drug operation because of the microscopic margin for error. (VGH Foundation)

"It's not in a drug dealer's interest to be killing everyone who is buying these drugs," Wood told CBC News. "The danger is making something so potent that a small difference in the mass or volume is the difference between being toxic or producing the desired effect in users."

"If someone is making these counterfeit pills in a basement, and a small amount spills over or is improperly measured, that can be the difference," he said. 

Wood likens the W-18 situation to how opium smoking transformed into the heroin trade as a more concentrated form of the drug was developed to allow for easier smuggling across international borders.

"It's exactly the same narrative that we're having today." he said. 

Minuscule margin of error

Unlike heroin, however, W-18 isn't derived from a plant and can be produced in a basement at a potency so high that the margin for error in making a pill with the desired amount of drug versus a deadly amount is microscopic, requiring the kind of quality control not usually found in illicit drug operations.

"This W-18, it seems to be crossing over the threshold to where it would be undesirable to makers in clandestine laboratories because you would be dealing with something that is so minuscule in mass that it would have to be cut hundreds of times in volume with another substance as the substrate." he said. 

"You'd need very sophisticated measures to be able to produce a street drug that didn't just kill people that were using it," he said.

"I think that's what's being seen with fentanyl. People are slipping up and making it just too potent."

With files from Brady Strachan