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Study finds ‘scarce evidence’ to support cannabis as a treatment for mental health disorders

WATCH: The health effects of cannabis have been a polarizing debate for the last century. Global News looked at the latest research and spoke to a medical professional covering topics such as lung cancer, mental health and brain development — to name a few.

Although many people use cannabis to help with symptoms of anxiety and depression, there’s not much evidence to support that use, according to a new study.

A systematic review published Monday in the journal Lancet Psychiatry reviewed existing research on cannabis as a treatment for anxiety, depression, attention-deficit hyperactivity disorder (ADHD), Tourette syndrome, post-traumatic stress disorder (PTSD) and psychosis.

After looking through 83 studies, the most favourable evidence the authors found was some poor-quality evidence suggesting that cannabis could slightly improve anxiety symptoms in patients who had other chronic conditions, like multiple sclerosis or chronic non-cancer pain.

Otherwise, they said there is “scarce evidence” to suggest that cannabis improves the symptoms of any of the above disorders.

READ MORE: Pot use linked to higher risk of depression, suicide in teens, study finds

“Cannabinoids are often advocated as a treatment for various mental health conditions,” said study author Louisa Degenhardt of the National Drug and Alcohol Research Centre at the University of New South Wales, Sydney, in a statement.

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“Clinicians and consumers need to be aware of the low quality and quantity of evidence for the effectiveness of the effectiveness of medicinal cannabinoids in treating mental health disorders and the potential risk of adverse events.”

“We don’t have a lot of evidence for what people commonly believe,” said Dr. Randi McCabe, a professor of psychiatry and behavioural neuroscience at McMaster University, and clinical director of the mental health program at St. Joseph’s Healthcare in Hamilton.

READ MORE: Marijuana just one element of mental health treatment, users say

One of the biggest problems the authors highlighted was just how few studies there were. For example, most studies of cannabis and depression or anxiety involved patients who had a primary diagnosis of some other condition, like multiple sclerosis.

So even for the favourable studies, “They had slight improvements in anxiety, but that could be because the cannabis helped with their pain or their MS symptoms,” McCabe said.

The study authors say there is a need for more robust, high-quality research on cannabis as a treatment for mental health disorders.

Highs and lows of Canada legalizing recreational cannabis
Highs and lows of Canada legalizing recreational cannabis

Even without that evidence, people are using it.

In a recent survey of patients arriving at McCabe’s anxiety clinic, 39 per cent reported using cannabis in the past six months. Of those, 43 per cent reported using it multiple times per week.

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These people might be using cannabis because they think it will help, she said, or they’re maybe self-medicating with it in the absence of other treatments. Or, it might be linked to their symptoms — she’s not sure at this point.

READ MORE: Teens turn to marijuana to self-medicate for stress, anxiety, report finds

Whether or not there is any evidence supporting its use, information suggesting that cannabis can help with common mental health conditions is “everywhere,” she said.

“I saw an ad on a bus the other day about how cannabis can help, it was selling a particular type of cannabis, how it could help with anxiety and depression. So I think people aren’t really discerning in looking for evidence, and sometimes it’s hard to get to primary evidence.

“They see these claims, or their friends are using it and say, ‘Oh, this helped me.’”

Health Series: The Future of Cannabis in the Medical Sector
Health Series: The Future of Cannabis in the Medical Sector

One question she has is whether using cannabis could actually interfere with the effectiveness of proven treatments for mental health disorders — things like cognitive behavioural therapy, which have years of research supporting their use.

While she doesn’t know the answer yet, her research group is looking into this.

In an editorial linked to the study, Dr. Deepak D’Souza, a professor of psychiatry at Yale University, wonders if doctors are putting “the cart before the horse” when it comes to recommending cannabis to treat mental health problems.

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Approved medications already exist for many conditions, he wrote. “And although one might argue that these medications have little efficacy and significant side-effects, at least they were tested in adequately powered, large, double-blind, randomised controlled trials and then subjected to a rigorous regulatory approval process.”

It’s unlikely that cannabis would meet the standards set for drug approval by government agencies like the U.S. Food and Drug Administration, he wrote.

READ MORE: Western University researchers show how CBD blocks side-effects of THC in cannabis

While she would have liked cannabis to have to meet the same standards as other mental health treatment options, it’s a little late now, McCabe said. With legalization, “the train left the station and now anybody can get it.”

Although she acknowledges that there are barriers to receiving mental health treatment, she recommends that patients have a conversation with a health professional about the evidence-based treatments that are available.

“I would talk to them about what are the treatments that we have evidence for that really work, and maybe answer their questions about it and see which one might be a good fit for them.”

Right now, the evidence isn’t there for cannabis, she said.

“Eventually it will be nice to have the evidence that says, ‘Hey if you have CBD oil in this amount, it will help with panic,’” McCabe said. “But we don’t know that, and it may not help a panic and it actually may make you worse.

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“So until we have that data, yeah, I agree that it probably shouldn’t be prescribed.”