Alexis Brenner's life changed for the better when she discovered that cannabidiol, a compound contained in cannabis, helped her manage chronic pain from endometriosis and fibromyalgia.

"CBD, once I found it, made a huge difference for my level of function," she said. "It's non-psychoactive, so I can be present and available and aware with my kids. I can use that medicine on a daily basis."

Brenner signed up with Health Canada-licensed marijuana producer Tweed, and started ordering cannabidiol oil. But in early 2017, she hit a roadblock.

"After using it for a few months, I went to go buy some more, and they were out. And when I called to ask them when it was going to be back, they said, 'We won't have it for another six weeks, and when it does come back I suggest you buy a few bottles, because we do not know how the supply is going to be.'"

Brenner isn't the only medical marijuana patient to report supply shortages from licensed medical marijuana producers. In some cases, those patients end up turning to the black market to find a reliable supply of medication.

Jaimee, who also uses medical cannabis to treat chronic pain, is one of those patients. She was using a high-THC strain of dried marijuana from Bedrocan to manage her condition, until a shortage prevented her from ordering more. (Like Tweed, Bedrocan is a subsidiary of Canopy Growth Corporation.)

Six weeks, when you're in pain, is a very long time to wait for medicine. - Alexis Brenner , medical cannabis user

"Every time I'd go to place an order or go to look to see if they had it or if they had any new strains, it would constantly be out of stock," she said.

After that, said Jaimee, "I've had to resort to either black market dispensaries or their lower [THC] strains, which don't do anything. So it's basically wasting money, to me."

CBC News has agreed to withhold Jaimee's last name, because she fears losing her Health Canada registration if she's identified as buying illegal marijuana.

Shortages reported as patient numbers grow

Licensed medical marijuana producers are trying to keep pace with extraordinary growth in the number of patients signing up for Health Canada's legal regime, said Jordan Sinclair, a spokesperson for Canopy Growth Corporation.

"And through that process, there's periods where you don't have every single type of every strain," Sinclair said.

Health Canada data confirms that the number of registered patients has grown quickly, with the federal agency reporting 90,208 new clients from December 2015 to December 2016 — an annual increase of 227 per cent.

Data from Health Canada shows licensed marijuana producers held 18,087 kilograms of dried cannabis in their inventories as of Dec. 31, 2016, but some clients are still reporting product shortages. (Sean Kilpatrick/Canadian Press)

On the surface, Health Canada's raw data suggests those patients should have access to plenty of medical marijuana. Public data from the agency shows licensed producers held 18,087 kilograms of dried marijuana in their inventories as of Dec. 31, 2016, plus 3,724 kilograms of cannabis oil. For both types of product, the amount in inventories has steadily increased since 2015.

"Based on market data, there is sufficient supply of cannabis for medical purposes to meet the current needs of registered clients," a Health Canada spokesperson told CBC News.

But Brad Martin, a medical cannabis user who tracks product availability from licensed producers and publishes it at CannStandard.ca, said it's "very common" to see certain products out of stock across multiple licensed producers.

"Every time I do my scan, I will see one licensed producer that doesn't have any availability," Martin said.

The president of a group of medical marijuana prescription clinics said his staff are aware of the shortages.

"We deal with probably around 15 or 16 different licensed producers, and out of those there's half a dozen that will no longer take registration because they've got to be able to supply the patients that they have registered," said Terry Roycroft, president of Medicinal Cannabis Resource Centre Inc.

"There is product available, but in certain cases the patients don't want that specific product. Or the reputations of that particular [licensed producer] aren't as positive as people may want to see, and so they're not buying from it," said Roycroft, citing product recalls for pesticide contamination as one possible reason patients might avoid certain producers.

Patients face difficulty switching producers

If medical cannabis patients can't get what they need from one licensed producer, noted Roycroft, they can always sign up with another. But patients interviewed by CBC News said the process of switching registrations can be time-consuming and inconvenient.

Health Canada reports 90,208 new medical cannabis clients between December 2015 and December 2016. (Sean Kilpatrick/Canadian Press)

Roycroft said some prescription clinics need to make it easier for patients to switch producers.

"There's absolutely no reason why they shouldn't be able to go back to the original clinic that they went to, and within a day, get new documentation," he said.

Canopy Growth spokesperson Jordan Sinclair said his company was trying to mitigate the difficulty of signing up with multiple licensed producers by offering products from different companies in a recently launched online store, Tweed Mainstreet.

"We hope that that will address some of the shortages that exist in the market, because it allows you to organize the demand more efficiently," Sinclair said.

Last week, Health Canada announced it was working to speed up the lengthy process for licensing new marijuana producers, as well as making changes that will allow existing producers to expand their facilities more quickly.

Those changes came too late to address the supply shortage experienced by Alexis Brenner, the chronic pain patient who was told she'd have to wait as long as six weeks to order CBD oil again. She recently switched from Tweed to another licensed producer.

"Six weeks, when you're in pain, is a very long time to wait for medicine," she said. "And that wouldn't be acceptable for patients that were on opioid painkillers."