Canadians buying legal marijuana have a much slimmer selection than their American counterparts. That's because Health Canada-licensed producers are allowed to sell only dried cannabis through the mail to registered patients and must stay away from "edibles" or other forms of the drug that are regulated south of the border.

However, like medicinal and recreational pot sold in Washington State, Canada's 17 licensed producers offer dozens of strains of dried leaves that help patients treat a range symptoms. Canadian producers must also display the potency of the batch's tetrahydrocannabinol (THC) and cannabidiol (CBD) content, as enforced under the federal Ministry of Health's current Marijuana for Medical Purposes Regulations.

Canadians can get pot prescriptions for up to 12 months from their doctors, but they don't typically recommend a particular strain, licensed producers say. It is up to patients to determine whether they want more of the psychoactive ingredient THC or CBD, which is reportedly the more medicinal component.

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David Brown, communications director at Vancouver-based Lift, a startup that acts as an online guide for medical marijuana patients, said most people are looking for strains high in THC content, which can reach up to 29 per cent. But pot with THC and CBD at roughly the same levels (around 9 per cent each) is becoming increasingly popular, he added. Mr. Brown said little research has been done on CBD's therapeutic benefits, but parents across North America have heralded cannabis products high in CBD and low in THC for stopping or slowing down seizures in their children while not getting them high. The strain with the highest CBD content offered by a licensed producer is about 17 per cent, which is "basically almost hemp," Mr. Brown said.

People searching out edible cannabis products can buy them illegally in Canada from street dealers or dispensaries, which have exploded in Vancouver to more than 60 storefronts in the past several years and are now popping up in other communities around the country.

Those dispensaries, technically operating illegally, can label their products with any level of THC or CBD, because they are not forced to do any scientific testing of their cannabis. On the other hand, licensed producers must do their own comprehensive testing to accepted standards and have the results verified by Health Canada inspectors.

"The one or two big differences between MMPR and dispensaries is you know exactly what you're getting from the MMPR everything is tested, everything is consistent, they have to by the regulations," Mr. Brown said. "Getting a reliable CBD strain from the grey market is very challenging – there's only two or three dispensaries that I know of who do third-party lab testing."

Greg Engel, CEO of Tilray, one of Canada's largest licensed producers, said in-house scientists test the pot for mould, bacteria and CBD and THC strength at the company's Nanaimo facility and send samples to one of the 10 third-party labs approved by Health Canada for further checks.

Chris Stone, a microbiologist and quality assurance manager at Broken Coast Cannabis, said Health Canada inspectors tour the facility on Vancouver Island about once a month. He said since the company started selling marijuana last November, inspectors have not taken a random sample of marijuana; instead the onus is on Broken Coast to keep comprehensive records that verify the third party that tests the product is using validated methods, as required by law.

A Health Canada spokesperson said the department's inspectors are authorized to examine any substance and collect samples at any licensed producer. To date, Health Canada has issued one recall due to THC content in a batch being slightly higher than labelled and four recalls over contamination from mould or other bacteria.

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Mr. Stone said he is under the impression that on the West Coast there are only a handful of licensed inspectors working out of a Burnaby, B.C., office that also handles many other controlled substances. He said that it often takes weeks for Health Canada to respond to his simple questions about how to adhere to the relatively new regulations and that inspectors seem "like they're under a lot of pressure to handle a lot of cases and issues."