From the Editor

“In the USA and Europe, the concentration of THC has more than doubled over the past 10 years…”

So notes a new paper in The Lancet Psychiatry.

Canada legalized cannabis for recreational purposes four years ago; other countries have done the same, as have almost two dozen US states. But how has cannabis itself changed over time? What are the implications for mental health disorders? And public policy? In the first selection, quoted above, Kat Petrilli (of the University of Bath) and her co-authors do a systematic review of cannabis potency and mental health and attempt to answer these questions. Drawing on 20 studies, they find: “Overall, the evidence suggests that the use of higher potency cannabis, compared with lower potency cannabis, is associated with an increased risk of psychosis, and this risk is higher in people who use cannabis daily.” We look at the paper and weigh its clinical implications.

In the second selection, using Ontario data, Dr. Daniel T. Myran (of the University of Ottawa) and his co-authors consider the effect of edible cannabis legalization on poisonings of children. Writing for The New England Journal of Medicine, they compare jurisdictions with legal sales (Alberta, British Columbia, and Ontario) with a province that hasn’t legalized that form of cannabis (Quebec). “Our data indicate that legalization was associated with marked increases in hospitalizations for cannabis poisoning in children.”

And, in the third selection, Shirley Nicholson writes about substance and stigma with a deeply personal essay. In this piece for CBC First Person, she discusses her son’s struggles and his death from an overdose. She writes: “He didn’t plan to die at 27. He was more than his addictions. He was our son, our brother, our grandson, our nephew, our cousin and we all loved him so.”


Selection 1: “Association of cannabis potency with mental ill health and addiction: a systematic review”

Kat Petrilli, Shelan Ofori, Lindsey Hines, et al.

The Lancet Psychiatry, 25 July 2022  Online First

Cannabis is the third most commonly used drug globally, after alcohol and nicotine. The cannabis plant produces at least 144 cannabinoids, with the main psychoactive cannabinoid being Δ9-tetrahydrocannabinol (THC). Experimental studies show that THC causes intoxication, cognitive impairment, anxiety, and transient psychosis-like experiences. The effects of THC are dose dependent, which means that higher potency cannabis products (products with high THC concentrations) could increase the risk of harm to cannabis users.

Understanding the health effects of higher potency cannabis products is timely because THC concentrations in cannabis have increased globally in recent decades. In the USA and Europe, the concentration of THC has more than doubled over the past 10 years, and new legal markets have facilitated the rapid development of cannabis products with higher potencies than earlier products, such as concentrated extracts…

Cannabis use has consistently been associated with mental health disorders. Heavy cannabis use has been associated with a four-times increased risk of psychosis, and this relationship is dose dependent. Cannabis use has also been associated with increased odds of developing depressive, as well as anxiety disorders… Because of the dose-response effects of THC on symptoms of acute mental health disorders, the potency of cannabis products could be a key factor determining the health effects of cannabis use.

Here’s what they did:

“We present, to our knowledge, the first systematic review of the association of cannabis potency with mental health and addiction… We searched Embase, PsycINFO, and MEDLINE (from database inception to Jan 14, 2021). Included studies were observational studies of human participants comparing the association of high-potency cannabis (products with a higher concentration of THC) and low-potency cannabis (products with a lower concentration of THC), as defined by the studies included, with depression, anxiety, psychosis, or cannabis use disorder (CUD).”

Here’s what they found:

  • “Of 4171 articles screened, 20 met the eligibility criteria: eight studies focused on psychosis, eight on anxiety, seven on depression, and six on CUD.”
  • Psychosis. The authors found several studies. With regard to risk: “Risk of psychosis diagnosis was assessed in four studies. Overall, the studies reported increased risk of psychosis with use of higher potency cannabis compared with lower potency cannabis. The GAP study included participants with first-episode psychosis and a control group from the same geographical area who did not meet the criteria for current or previous psychotic disorder. In a preliminary analysis (n=454), patients with first-episode psychosis were more likely to use higher potency cannabis than the control groups…”
  • Studies also found more symptoms of psychosis and a higher risk of relapse with higher potency cannabis.
  • Anxiety. There were several studies but all of poorer quality. The evidence was mixed. For instance, “Use of higher potency cannabis was associated with a two-times increased risk of generalised anxiety disorder, compared with lower potency cannabis, in a sample of 1087 people who had used cannabis in the past year (OR 1.92…)… In another study (n=181 870), the risk of anxiety diagnosis was not higher for people who used higher potency herbal cannabis compared with people who used lower potency herbal cannabis (1.05…)” In a third study, however, no connection was found.
  • Depression. Only one study was fair in quality; the rest were poor. “In a study (n=181 870) done in 20 countries (typically high-income countries), use of higher potency cannabis concentrate (OR 1.34…) and higher potency herbal cannabis (1.18), compared with lower potency herbal cannabis, were associated with a slight increase in odds of depression diagnosis. Conversely, in a UK sample of 1087 people who used cannabis in the past year, there was little evidence to suggest an increased risk of major depression in people who used higher potency cannabis compared with people who used lower potency cannabis…”
  • CUD. They found six studies – though the overall quality was found to be poor. For example, “Increased risk of dependence was reported in a sample of Japanese patients (n=71), with the use of high-potency cannabis associated with a seven-times increased risk of dependence syndrome compared with people who use lower potency cannabis (OR 6.9…)”

“Overall, use of higher potency cannabis, relative to lower potency cannabis, was associated with an increased risk of psychosis and CUD. Evidence varied for depression and anxiety.”

A few thoughts:

1. This is a timely study.

2. The main finding isn’t exactly surprising.

3. The quality of the papers was uneven at best. As the authors note: “None of the studies were categorised as good quality from the risk of bias assessment.” And there were problems in terms of the consistency of the definition of high and low potencies.

4. As I’ve commented before, these are early days in terms of cannabis research.

5. CBD wasn’t part of the review. (!!)

6. When speaking to patients, particularly those who may have experimented with cannabis in years past, mentioning the increased potency would be important.

7. The implications for public policy? “The findings support recommendations to discourage the use of higher potency cannabis products for low risk use.” Is more government labelling appropriate? Are stronger regulations needed?

The full Lancet Psychiatry paper can be found here:

Selection 2: “Edible Cannabis Legalization and Unintentional Poisonings in Children”

Daniel T. Myran, Peter Tanuseputro, Nathalie Auger, et al.

The New England Journal of Medicine, 25 August 2022

Unintentional cannabis poisoning in children may be a consequence of legalizing cannabis for adult use, although the effect of legalization with or without the sale of cannabis edibles on cases of ingestion in children is unclear. In October 2018, Canada legalized the sale of dried cannabis flower to adults for nonmedical use. Starting in January 2020, the sale of edible products (e.g., gummies, chocolates, and baked goods) with tetrahydrocannabinol (THC) was approved. Although all provinces were required to allow the sale of cannabis flower, each province could choose to restrict sales of edibles. Alberta, British Columbia, and Ontario (combined population, 24.3 million) allowed the sale of a wide variety of edibles starting in January 2020. In contrast, Quebec (population, 8.6 million) prohibited the sale of edibles, which provides an opportunity to study the contribution of edibles to changes in poisonings in children after legalization of cannabis.

So begins a letter by Myran et al.

Here’s what they did:

“We conducted a population-based study examining the association between legalization and unintentional cannabis poisonings in children by analyzing data on all hospitalizations in children 0 to 9 years of age in Alberta, British Columbia, Ontario, and Quebec (86% of the Canadian population). We compared hospitalization rates over three periods: before legalization (January 2015 through September 2018); the first period of legalization, when the sale of only dried cannabis flower was legalized in all provinces (October 2018 through December 2019); and the second period of legalization, when edibles were permitted in Alberta, British Columbia, and Ontario (exposed provinces) but prohibited in Quebec (control province) (January 2020 through September 2021).”

Here’s what they found:

  • There were 581 hospitalizations of children for cannabis poisoning.
  • Demographics. The majority were boys (53.9%); the mean age was 3.6 years.
  • Before legalization. “Hospitalization rates were similar across provinces (0.95 per 100,000 person-years in exposed provinces vs. 0.93 per 100,000 person-years in the control province.”
  • After legalization. “Hospitalization rates in the exposed and control provinces during the first period of legalization were 2.6 times as high as those before legalization. During the second period of legalization, the hospitalization rate in exposed provinces (7.15 per 100,00 person-years) was 7.5 times as high as before legalization (incidence rate ratio, 7.49…), whereas the hospitalization rate in the control province (2.82 per 100,000 person-years) was 3.0 times as high as before legalization (incidence rate ratio, 3.04…) but was similar to the rate during the first period of legalization (incidence rate ratio, 1.18…).”

A few thoughts:

1. This is good and interesting data.

2. The implications for policy? “Our findings suggest that restrictions on the sale of visually attractive and palatable cannabis edible products are key policy considerations for the prevention of cannabis poisonings among children in the United States and other countries”

3. A major change like cannabis legalization has unintended consequences. Over the coming years, policy makers need to address them.

The letter can be found here:

Selection 3: My son was more than ‘just’ an addict

Shirley Nicholson

CBC First Person, 30 July 2022

My son was just an addict. 

That’s what some people say. He was nothing but an addict. Like he planned this. Like he really didn’t want to live. 

But he was so much more than his addictions. He was our son. He was someone’s brother. He was someone’s grandson, nephew and cousin. He was loved so much. He loved us.

So begins an essay by Nicholson.

She considers her son and substance misuse:

“From everything I’ve learned about my son’s addiction to alcohol and drugs, the craving, the need and the desperation to have that fix never goes away. Some can work past it. Some can go to Narcotics Anonymous or a rehab program and work their way through it. The need to stay sober must be stronger than the need to get a fix.

“People say it’s a choice. What I saw from my son’s behaviour is that addicts don’t really have a choice. The addiction has the control, the power, the say in whether they use again.”

She describes the loss, which had come a few hours after their last call.

“From the moment the police came to our door and gave us the horrific news, we’re just putting one foot in front of the other, one step at a time. Some days we get through with relative ease and only a few moments of utter desolation. On other days, we can barely crawl out of bed to face the day.”

The loss colours so much of her life. She recounts even “falling apart” in the grocery store (her son loved to recite a commercial about Frank’s RedHot sauce). She ends: “If love could have saved our son, he would surely be alive and well today. If love could have … but it didn’t. He was our beautiful boy. Our energetic little guy who could make best friends at the playground. He was our handsome young man who could charm the girls… He had ideas, plans, dreams and a motorcycle test appointment the next week.”

A couple of thoughts:

1. This essay is deeply moving and raw.

2. It’s an important essay – and Nicholson probably struggled to write it. We should be grateful.

The full CBC First Person article can be found here:

Reading of the Week. Every week I pick articles and papers from the world of Psychiatry.