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A cannabis plant is shown in southwest Quebec.

Justin Tang/The Canadian Press

Canada's biggest licensed marijuana producer plans to subject its products to enhanced testing for pesticides and other contaminants, as the industry seeks to restore consumer confidence amid a tainted cannabis scare.

Canopy Growth Corp., which owns the Tweed, Bedrocan, and Mettrum brands, will unveil a new testing regime on Wednesday that it hopes will reassure customers that the products haven't been exposed to dangerous chemicals. The move comes after The Globe and Mail revealed in December that a recall of medical marijuana at Mettrum was due to the discovery of myclobutanil, a banned pesticide that is not permitted for use on cannabis because it emits hydrogen cyanide when heated and can lead to serious health problems. A similar recall was announced at rival producer Organigram soon after.

Canopy, which purchased Mettrum in January, said it would implement new measures to ensure such a recall doesn't happen again.

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Globe investigation: What's in your weed?

Read more: Mulcair calls out Trudeau on 'hypocrisy' in marijuana anecdote

Since the recall, Health Canada has required Mettrum and Organigram to have their products independently tested at federally accredited labs before they are shipped to customers. The regulator also announced that the rest of the industry – roughly three dozen companies – will be subject to random screening.

Little is known about how the program will work, and whether it will be effective in protecting consumers. In addition to the new testing requirements for Mettrum, Canopy says it will introduce its own system of monthly random tests across all of its operations, which will be conducted in addition to any random testing done by Health Canada.

At least one product lot from its Tweed facility in Smiths Falls, Ont., will be randomly screened each month, along with one lot from its Tweed Farms facility in Southern Ontario, and one lot from the Bedrocan operation. The random testing covers roughly one-tenth of the production from each facility in a given month, Canopy chief executive officer Bruce Linton said.

The screening will be conducted by an independent, federally accredited laboratory, and the selection of each sample will be managed by the company's quality assurance official, with the results posted on the company's website, Mr. Linton said. Growers responsible for each crop will have no say in the random sample each month, and the company may expand the testing to multiple lots some months, he added.

Canopy is the latest in a series of companies to introduce independent testing programs amid the tainted cannabis controversy that now hangs over the industry.

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In February, Saskatchewan-based CanniMed Therapeutics Inc. posted test results for some of its products online to demonstrate they were free of banned chemicals. In March, Aurora Cannabis, which issued a recall over a bulk shipment it purchased from Organigram, announced it would begin testing products and posting the results online for consumers to scrutinize. Soon after, the Cannabis Canada Association (CCA), which represents 15 federally licensed companies, said it would follow suit with a similar initiative.

However, there are still no uniform measures in place from the government to ensure consumer safety in the industry. Meanwhile, dozens of patients have told The Globe they have become seriously ill from exposure to the tainted products, and now suffer breathing difficulty, persistent pain, headaches, nausea and rashes, among other problems.

The recalls have raised troubling questions about Health Canada's oversight of the sector, particularly as the federal government prepares to legalize cannabis for recreational use next year. Though the federal government has touted the licensed producers as safe, medical-grade product, Health Canada acknowledged to The Globe in January that is was not testing those companies to ensure that they weren't using dangerous chemicals to help their crops.

Health Canada figured it didn't need to screen the industry for safety because the companies knew what chemicals were banned, and therefore shouldn't be using them. The companies were essentially left to police themselves.

But in an industry where crops can be worth hundreds of thousands of dollars and companies can ill afford to lose that revenue due to pests, growers may resort to unauthorized chemicals as a shortcut to save their plants, rather than anger shareholders with financial losses. Meanwhile, growers at many companies are incentivized based on crop yields, and may be further tempted to use chemical shortcuts to boost their output, despite the harm it can do to patients.

A former employee of Mettrum told The Globe the company used myclobutanil to control mildew on plants as far back as 2014, knowing it was banned. To avoid detection, staff hid the chemicals in the ceiling tiles whenever Health Canada inspectors visited the site, knowing that the regulator wasn't testing the plants.

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Some producers believe Health Canada needs to strengthen its approach to testing in order to protect patients. Aphria Inc., one of the 15 companies in the CCA that pledged to post independent test results online, recently said Health Canada should enforce regular testing across the industry, and have it funded by the industry through a fee paid to the government. Mr. Linton agreed, and said Canopy would support such a model.

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