Health Canada is standing by its claim that the drug W-18 is a "synthetic opioid" that's "100 times stronger than fentanyl," despite criticisms from addictions and pharmacology experts who say that it may be flatly false.

Over the past few months police forces and provincial health authorities across the country have described W-18 the same way, with some declaring it the deadliest in human history. Media, including VICE News, has picked up on those descriptions.

Police have found the drug in two separate investigations, and more recently they've said it was responsible for the death of a Calgary man who overdosed on a cocktail of W-18 and other drugs, Health Canada banned the drug this week, officially making it illegal to possess, sell, and import it.

"Substances like W-18 are dangerous and have a significant negative impact on some of the most vulnerable people in our society. I am pleased with the swift action that Health Canada has taken to regulate the substance," Health Minister Jane Philpott wrote in a press release Wednesday.

However, there's very little scientific data available about the drug, and how it impacts humans. And a number of doctors and scientists are urging the government to get its facts straight on W-18.

Doctor Hakique Virani first heard about a new street drug called W-18 about two years ago from patients he works with at his methadone clinic in downtown Edmonton, Alberta. Most of them are seeking treatment for opiate addictions, including fentanyl, as the province continues to grapple with a spike in drug overdose deaths.

"Some of them told me they had been sold W-18 by drug dealers from Vancouver. And that it was this highly potent opioid," Virani said in an interview this week.

At first Virani accepted such claims as truth, until he looked at the original science behind the substance, including the data included in the original patent for it that was published in the 1980s.

"What we can say is that W-18 may well not be an opioid and that the assumptions that lead to the conclusion that it's an extremely powerful opioid were leaps at best and clearly there's more work to be done to characterize how this molecule works in human beings," Virani said.

For him, it's important for public health officials to work toward busting the myths that can cloud sound judgment and responses toward it.

"W-18 could be an antihistamine, extremely powerful one, maybe an anti-inflammatory," Virani said. "All we know is that when you shot a mouse up with it, the mouse stop writhing in pain ... It slept for days, and woke up hungry and thirsty. That's not consistent with the effects of an opioid."

The only study that exists on W-18 is found in the patent published in 1984 by the pharmacologists at the University of Alberta who invented the drug, along with 31 other W-series compounds. Tests of the substances were conducted on mice compared to morphine, and the 18th compound, W-18, was found to have the strongest.

No human trials involving the substances have ever been conducted. It has also never been studied in comparison to fentanyl.

Ed Knaus, the lead researcher on the team who retired seven years ago, did not respond to requests for comment from VICE News — and hasn't spoken to media in months — but he told Maclean's magazine in February that the goal of his experiments was to create a non-addictive painkiller.

However, the patent was never bought by a drug company and so the patent lapsed. Knaus abandoned the project. Yet, somehow, the formula has been discovered by fake drug labs in China and elsewhere and sold online. "It doesn't make me feel good that people have picked this up," said Knaus.

Virani, who used to work for Health Canada, says he is pleased to see that the substance has been banned, but stressed that W-18 has never been tested on humans and that means there's more work to be done before we can conclude its effects on humans.

"When you're the health authority of the land, you have to get the facts right," he said.

"I can see how these conclusions about W-18 came about, especially given our great concern about opioids right now. But it's just inaccurate," he added. While all of this doesn't mean that W-18 isn't highly toxic, we still don't know enough about it at this point to say exactly how dangerous it really is for human consumption.

"There's really nothing known for certain about its pharmacological properties. You could say it's more than 1,000 times more potent than aspirin, but that doesn't raise the same sorts of alarms."

Virani also warned that inaccurate information about W-18's potency could create a false sense of tolerance among drug users. "If someone thinks they have been exposed to W-18 and nothing bad happened to them, they might be inclined to take more risks if they think they survived something that was 100 times stronger than fentanyl," he said.

It's likely that sometime next week, there will finally be some answers about W-18, as pharmacology researchers at University of North Carolina plan to release the first comprehensive scientific study on the substance since the 1980s.

Bryan Roth, the team's lead researcher who also runs what he says is the largest drug screening center in the world, spoke to VICE News on his way into a drug conference at Northeastern University in Boston on Thursday where he will present his findings before making them publicly available.

Roth says W-18 appeared on his team's radar about two years ago, but they didn't find anything particularly interesting about it at the time. They decided to go back and investigate the substance a couple months ago after increased public interest towards it. They were able to secure samples of it through a chemical supplier who creates compounds for scientific research.

He says he doesn't know how people started comparing W-18 to fentanyl, but suggests the idea could come from the fact that it was originally created to be an analogue to fentanyl. "But if you look at it, it's quite dissimilar to fentanyl," he said. Also, he thinks drug dealers online could be marketing it as an opioid.

"And there's no scientific data for that either. The only data is in the patent literature, and there's no data there that it's an opioid. There's really nothing known for certain about its pharmacological properties. You could say it's more than 1,000 times more potent than aspirin, but that doesn't raise the same sorts of alarms."

Roth wouldn't reveal much about his study, saying that he wanted to wait until next week when he posts his findings online. "At that time, a lot of people are going to realize they have been very unclear about how it works," he chuckled.

"And even then, once real scientific data gets out there, it can take awhile for it to really seep into the consciousness of people."

A spokesperson for Health Canada acknowledged in an email to VICE News that when it comes to W-18, "current evidence is limited."

"What is available suggests that W-18 is an extremely potent analgesic [pain reliever], with one test on mice showing W-18 to be up to 10,000 times more active an analgesic than morphine (which would be roughly 100 times stronger than fentanyl)."

The email concluded that the department is monitoring evidence on the drug as it evolves, and it's also "aware that there have been blog entries and other reports, thus far unconfirmed, that the pharmacology of W-18 may be different from that reported in the original patent."