Health Canada's restrictive approach to marijuana safety testing is putting the public at risk, a growing chorus of scientists and activists warns – saying consumers are potentially being exposed to contamination in products that are widely accessible since the federal Liberals took power promising legalization.

A number of laboratories accredited by Health Canada say the regulator has repeatedly discouraged them from analyzing any cannabis that does not come directly from one of the country's 31 licensed medical marijuana producers – even as hundreds of dispensaries have sprouted up in Vancouver and Toronto, flooding the market with products of unknown provenance. Patients' requests to have their federally licensed medical marijuana tested to ensure its safety are also blocked.

Testing done for The Globe and Mail showed that three of nine samples of dried cannabis from nine unregulated dispensaries would not meet Health Canada's safety standards for licensed growers.

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Globe Investigation: What's in your weed? We tested dispensary marijuana to find out (for subscribers)

Hubert Marceau, one of the owners of a lab in Saguenay, Que., that is accredited to analyze marijuana, said his facility has received at least a dozen requests from doctors, patients and dispensaries that want to know more about the contents of cannabis from both regulated and unregulated sources to ensure it is safe and free of contaminants.

The lab has waited as long as eight months for responses to requests for guidance from Health Canada, Mr. Marceau said – and when they come, they are usually imprecise.

"I asked: Can we test for physicians? Can we test for patients? And always the answer was either fuzzy, or we are waiting for more information, or I'm forwarding you to whatever department – and we often didn't get any answers."

Mr. Marceau said the ordeal has been frustrating: "Take a clear direction. Either go all in, or all out."

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On Thursday, The Globe and Mail published the results of an investigation into the contents of marijuana from nine unregulated Toronto dispensaries. Three of the nine samples of dried cannabis tested would not meet Health Canada's safety standards for the companies it licenses to grow for medical users. The investigation also revealed that labs have been warned not to test samples provided by anyone other than a licensed producer – a threat taken so seriously that the lab that tested for The Globe did so on condition that the newspaper would not identify the facility.

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Health Minister Jane Philpott could not be reached for comment on the matter.

Mr. Marceau said that, when the current medical marijuana laws came into effect in 2013, it seemed a natural fit for his business, Laboratoire PhytoChemia. The lab, which specializes in the chemistry of natural products, can pinpoint the amount of THC – the intoxicating compound in marijuana – and cannabidiol – the non-psychoactive, therapeutic compound – in a sample. But when consumers started asking his lab to test marijuana that had been produced under the previous legal regime, no one could give a clear answer.

Kirk Tousaw, a Vancouver lawyer who has argued several marijuana cases that have forced the government to change regulations, said he represented one lab that was told by Health Canada to stay away from unregulated cannabis.

"On one hand, we hear repeatedly from government, from Health Canada, that the cannabis that people grow for themselves, or that they purchase from dispensaries, is unsafe – largely because it is untested and of uncertain quality," Mr. Tousaw said. "So if it believes it to be true, then by preventing labs from testing for home producers or patients, they're actually creating harm and creating risk to critically and chronically ill Canadians, which is cynical and hypocritical to say the least."

Mr. Marceau said he also sought a legal opinion on the matter. The Globe spoke to officials at two other labs who said they have been frustrated in their efforts to get guidance from Health Canada on testing for safety.

The Globe's investigation found several different kinds of pathogenic bacteria in the dispensary samples, including one that also contained high levels of potentially harmful yeasts and mould, which can lead to serious health concerns if consumed. The operators of two dispensaries whose products failed the tests said they would have pulled it had they known of the contaminants.

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The government said in June it has concerns about dispensary products, but has not made access to safety testing a priority because it considers the product illegal.

"These operations are illegally supplied, and provide products that are untested, unregulated and that may be unsafe," the ministers of health, justice and public safety said in a statement while announcing a federal task force on marijuana legalization.