Health Canada retracts W-18 claims, citing lack of reliable information

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Health Canada has retracted claims about W-18, a little-known synthetic compound that only recently emerged in Canadian street drugs and has received considerable attention due to claims it is significantly more dangerous than fentanyl.

The federal department, which had described the drug as an "extremely dangerous synthetic opioid" that can be 100 times stronger than fentanyl, issued a statement this week saying there is a lack of reliable information about the "potentially harmful substance."

Health Canada said its previous messaging was intended to align with multiple credible sources, including the European Monitoring Centre for Drugs and Drug Addiction, which classified W-18 as an opioid. Limited research on the drug has also compared it to morphine, which is an opioid.

"However, doubts about this classification have been raised recently by a number of credible sources," the statement says. "It has been noted that, at present, while the only publicly available scientific report compares W-18 and related compounds to opioids, it does not determine whether or not W-18 binds to opioid receptors in the body."

W-18 was part of a series of chemicals manufactured and patented in Alberta in the mid-1980s for pain relief.

It has only been tested on mice and has never been marketed commercially. The series was eventually shelved.Earlier this month, after a months-long process, Health Canada made it illegal to produce, possess, import or export W-18.

Beginning last August, the drug turned up in the Calgary area, then Edmonton, Kelowna and Metro Vancouver. A man who fatally overdosed in south Calgary in March is the first confirmed case of a W-18-related death. The man also had heroin and 3-Methylfentanyl, a drug chemically similar to fentanyl, in his system.

Like the synthetic opioid fentanyl, W-18 is sometimes being sold on the streets as other drugs, such as heroin and oxycodone, police say. That similarity – and North America's current opioid crisis, driven in large part by the growing prevalence of fentanyl – has also drawn much attention to W-18.

Fentanyl has been detected in a larger percentage of fatal drug overdoses every year, reaching more than half of the 308 illicit drug overdose deaths in British Columbia from January through May of this year. In response, British Columbia declared a public-health emergency and intensified efforts to equip drug users and first responders with naloxone, a drug that can reverse the effects of an opioid overdose within minutes.

Not knowing the pharmacological makeup of W-18 means not knowing whether it's an opioid – or whether naloxone is effective in countering its effects.

"Naloxone will effectively reverse the effects of fentanyl, heroin, OxyContin – you name it," said David Juurlink, a toxicologist and drug safety researcher at the University of Toronto. "But it only has that effect for drugs that bind to opioid receptors in the brain, spinal cord.

"Because we have no reason to believe that W-18 is an opioid, we have no reason to believe that naloxone would reverse any of its effects – notwithstanding the fact that we don't know what any of those effects are."

The claim that W-18 is "100 times stronger than fentanyl" appears to have originated from the patent, filed in 1982, which detailed a pain test performed on mice.

"The idea is that you give mice a noxious stimulus and they writhe, and various chemicals will suppress that squirming," Dr. Juurlink said. The researchers found it took 10,000 times more morphine than W-18 to produce the same analgesic effect. Fentanyl, meanwhile, is 80 to 100 times more potent than morphine.

"That seems to be the basis for this 100-fold claim," Dr. Juurlink said. "There is no other evidence."

Health Canada acknowledged there are ongoing studies to determine "the mode of action of W-18" and said the department will assess new information as it becomes available.