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Cannabis complications: Sizing up the threat posed by side effect research agendas

April 12, 2023  By Denis Gertler

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This February, the International Congress on Clinical Trials on Cannabis met in London, U.K. where experts presented the latest findings on therapeutic uses and benefits of cannabis. 

Findings covered a wide range of areas such as improved survival of brain cancer patients, the world’s first clinical trial for treatment of anxiety, reduced pain from cluster headaches, and lessened inflammation affecting tooth loss. 

Treatment of chronic pain and some types of epilepsy are frequently mentioned. Also, that cannabis use may help people shed alcohol addiction and opioid dependency. 

Peer-reviewed literature has reported progress in treating symptoms of mental illness such as anxiety, depression, and PTSD. Help alleviating effects of chemotherapy is another observed outcome. And contrary to popular belief, studies have found evidence that cannabinoids can improve memory and learning performance. 


To be sure, there are also some red flags around cannabis use. 

Studies have found that cannabis may aggravate symptoms of bipolar disorder although there is very limited evidence that its use leads to bipolarity. There is moderate evidence that cannabis use may elevate risk of depression, suicidal ideation and perhaps psychoses such as schizophrenia, although there is no evidence that the incidence illness is affected by legal access. 

Lately, researchers have begun exploring connections between cannabis and respiratory illness and it’s here where the industry should perhaps be paying closer attention. 

A widely reported University of Ottawa/Ottawa Hospital study revealed an association between “marijuana” smoking and chronic damage to airways. According to the press release, researchers found that cannabis smokers have a higher rate of emphysema and airway diseases compared to cigarette smokers. 

The study examined the chest CT examinations of 56 marijuana smokers, 57 non-smokers and 33 tobacco-only smokers.

They determined higher rates of paraseptal emphysema and airway inflammatory changes, such as bronchiectasis, bronchial wall thickening, and mucoid impaction in cannabis smokers. 

Looking directly at the research, however, tells a markedly different story than the publicity. 

The paper’s authors own up to several key limitations. A tiny sample size is acknowledged, and an admission that causality cannot be inferred from the findings. Most concerning, 89 per cent of cannabis smokers (50 of 56) were also tobacco smokers, meaning that lung damage found in members of this cohort cannot be meaningfully attributed to cannabis use. 

The authors acknowledge that concomitant cigarette smoking among the cannabis cohort limits the study’s ability to draw strong conclusions.

Indeed, a more recent Australian study found evidence of impaired lung function by age 30 from tobacco smoking, but no discernable harm from long-term cannabis usage at lower levels.

Researchers also detected no added risk to lung function from co-use of tobacco and cannabis, versus risks associated with tobacco use alone. As the study’s authors put it, “cannabis use does not appear to be related to lung function even after years of use.”

Unlike the Ottawa research, the Australian study ran for thirty years (double the period of the Canadian trial) and involved several thousand now-adult children of pregnant women recruited into the cohort study between 1981 and 1983.

But the Ottawa initiative is not a one-off. It references 32 research papers addressing potential harms from cannabis use, and judging by the public messaging from the study, there seems to be an agenda to conflate tobacco and cannabis use. 

As Giselle Revah, one of the study authors is quoted as saying: “We still need more research before we can affect policy change. We need larger, more robust prospective studies with more patients.” I read that as stating there is an effort by some researchers to pursue an ill-supported bias against cannabis use, to corroborate harms like those known from tobacco. 

Research requires funding and with the heyday of tobacco research past, cannabis would seem to be a new candidate to focus efforts and conveniently, funding.

There is a resurgent prohibitionist ethos alive in medical research and public health communities, which we have seen with the recently revised Low-Risk Alcohol Drinking Guidelines, and I’m detecting its emergence on the cannabis scene. 

While Canada’s cannabis industry admittedly has more pressing business concerns, it’s time to squarely size-up the threat posed by ideologically driven research agendas. 

Denis Gertler is a regulatory consultant, board member, and former government regulator.

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