Cannabidiol, or CBD oil, is promoted for a wide range of medical conditions. Recently, a review for doctors weighed the science behind the claims.

The Clinicians' Guide to Cannabidiol and Hemp Oils was published earlier this month in the journal Mayo Clinic Proceedings.

CBD is a compound found in the cannabis plant. It is not intoxicating, Health Canada said.

As of October 2018, the sale of dried cannabis, fresh cannabis, cannabis oil, cannabis plants and cannabis seeds are permitted under the the Cannabis Act.

As consumer interest in CBD grows ahead of the Oct. 17 legalization of cannabis edibles, extracts and topicals, here's a primer to answer common questions about its health claims for seizures, pain and other conditions.

What is CBD approved to treat?

Epidiolex, a purified form of plant-based CBD, is the only CBD-related treatment approved by the U.S. Food and Drug Administration (FDA). It is used to treat severe forms of epilepsy . Epidiolex isn't listed in Health Canada's database of medications approved for use in this country.

Health Canada assigns a drug identification number (DIN) to all drug products evaluated and authorized for sale in this country. To qualify, a drug manufacturer needs to provide information including dosing, strength and how it's taken.

"Currently, there are two cannabis-related drugs that have a DIN and are authorized for sale in Canada," a spokesperson for Health Canada said in an email.

Nabilone, a synthetic tetrahydrocannabinol, or THC, product is approved to treat nausea. THC is the main psychoactive component in cannabis that gives users a high.

The other drug with a DIN is Sativex, which is manufactured from whole botanical extracts and contains THC and CBD, according to Health Canada. Sativex is added to treatments aimed at relieving spasticity in adults with multiple sclerosis. Spasticity is a muscle-control disorder.

No CBD-specific product has a DIN.

As well, no other "cannabis-related drug (including fresh or dried marijuana or cannabis oil) has been approved to be marketed as a drug for therapeutic use and sale in Canada," Health Canada said.

What is CBD commonly used for?

There are anecdotal reports from users of CBD helping with certain types of pain, such as nerve-related back pain.

"Chronic pain management continues to challenge patients and physicians alike, and investigation into potential therapies such as CBD and hemp oils is a promising area for the future of clinical pain management for both pain relief as well as addiction management," Dr. Karen Mauck, an internist at Mayo Clinic, and her co-authors wrote.

Dr. Hance Clarke, director of pain services at Toronto General Hospital who wasn't involved in the U.S. paper, said he starts by asking patients what symptoms they want to use CBD to treat.

It's one of the first times in Canadian history where a medication has made it to the population without the science actually leading us there. - Dr. Hance Clarke, director of pain services at Toronto General Hospital

"The evidence has not caught up to the story that's in the public," Clarke said. "It's tricky. It's one of the first times in Canadian history where a medication has made it to the population without the science actually leading us there."

The world is looking to Canada for answers on CBD, said Dr. Hance Clarke. (University Health Network)

Physicians need to work with patients to figure out what people are using, the levels in their body and what's actually helped and what hasn't.

"The world is looking to Canada over the next five to 10 years," Clarke said. An evidence-based perspective on cannabis is needed rather than solely industry's, he said.

Canada's Arthritis Society said there's limited clinical evidence so far on the relative benefits and risks of medical cannabis to treat osteoarthritis and rheumatoid arthritis.

CBD now is widely used by people for all kinds of disease, in particular anxiety, panic attack, bipolar disorder, depression. But we don't know if CBD is really good for these kind of diseases. - Dr. Gabriella Gobbi

In January, research into CBD's effects on pain and anxiety in lab rats was published in the scientific journal Pain .

"CBD now is widely used by people for all kinds of disease, in particular anxiety, panic attack, bipolar disorder, depression," said Dr. Gabriella Gobbi, the study's author and a psychiatrist at McGill University's faculty of medicine in Montreal. "But we don't know if CBD is really good for these kinds of diseases."

Only clinical trials in humans can show if CBD is really effective for an illness, Gobbi said.

In Canada, pharmaceutical companies are sponsoring clinical trials to test CBD products in people.

How do you know what's in the product?

Depending on what part of the plant is extracted, different components will be present in the oil, the Mayo Clinic authors said. Their list of what clinicians should look for includes:

Manufacturing standards certification, such as pesticide or herbicide testing.

European Union or Australian organic certification.

Lab testing to confirm cannabinoid levels and the absence of heavy metals.

"We see variations from batch to batch where patients are doing well on something, and potentially the next time they seek that same product, potentially they're not seeing the same effects," Clarke said.

A research letter published in 2017 in JAMA found nearly 70 per cent of CBD extracts sold online were mislabelled.

"A lot of CBD oil can have very little or contain lots of THC, so you must be very careful," Gobbi said. "We need more quality control."

What side-effects have been reported?

In larger studies on CBD treatment for epileptic patients, it was associated with drowsiness, decreased appetite and diarrhea in up to 36 per cent of people, the Mayo Clinic authors said, adding the side-effects were less severe and frequent compared with a conventional anticonvulsant medication.

CBD oil products can have very little of the active ingredient or contain a lot of THC, the main psychoactive component in cannabis that gives users a high. (Tijana Martin/The Canadian Press)

The FDA said its review of a marketing application for Epidiolex suggested potential for liver injury associated with CBD.

You can't just self-treat. - Dr. Gabriella Gobbi

"You can't just self-treat," Gobbi said.

What about drug interactions?

The main drug interactions doctors and pharmacists look for are drugs, such as morphine, oxycodone, sleeping pills, antidepressants or antipsychotics, that already make you sleepy, confused or impair co-ordination.

"If you're taking those medications to begin with and you use cannabis, we'd expect that those side effects would get worse," said Kelly Grindrod of the University of Waterloo's School of Pharmacy.

Doctors should look for lab testing to confirm cannabinoid levels when looking for products for patients, researchers say. (Guillaume Payen/SOPA Images/LightRocket/Getty)

People should talk to their physician, nurse or pharmacist to discuss potential drug interactions when determining whether to try CBD.

Maddie Brown, a registered practical nurse and cannabis consultant based in Ottawa, helps patients with medical cannabis prescriptions understand how CBD works and obtain it.

"I'm definitely most concerned about blood thinners," Brown told CBC Radio's White Coat, Black Art. "CBD can make Coumadin [a blood thinning medication] more potent."

The general advice is to start low and go slow, especially if taking medications that are known to interact, Grindrod said.