Higher potency cannabis associated with increased risk of psychosis and addiction – report

Garrett McGovern, a GP specialising in addiction, accepts that cannabis can trigger psychosis — but said the real issue is whether “proper regulation” of cannabis would be a better approach than prohibition.

Higher potency cannabis is associated with increased risk of psychosis and addiction, according to a new study.

The research — published in The Lancet Psychiatry and described as the first systematic review of the issue — has sparked renewed debate on what is often a polarising issue in Ireland and abroad.

Consultant psychiatrist Bobby Smyth said he was not surprised by the research. He said he was seeing on a weekly basis “the destructive impact” cannabis was having on young lives and said society seemed to be “blind to the epidemic”.

Meanwhile, Garrett McGovern, a GP specialising in addiction, said he accepted that cannabis, particularly high strength cannabis, can trigger psychosis — but said the real issue was whether “proper regulation” of the drug would be a better health approach than prohibition.

The research was led by a team from the University of Bath, assisted by colleagues from three other British universities, and identified 20 studies that examined the issue.

Potency increasing

The research said concentrations of THC — the main psychoactive compound in cannabis — had “more than doubled over the past 10 years”.

The average amount of THC in herbal cannabis (back) rose by around 40% between 2010 and 2020, while the potency of THC in cannabis resin (front) has doubled. File picture: Niall Carson/PA 

It also  said new legal markets, such as in the US, had facilitated the development of high potency products.

Last June, the European Monitoring Centre for Drugs and Drug Addiction said the average THC in cannabis resin — traditionally weaker than cannabis herb — had more than doubled between 2010 and 2020 and now ranged between 17% and 25%.

It said the average THC in cannabis herb had increased around 40% between 2010 and 2020 and that potency ranged between 7% and 14%.

The Lancet research said: “To our knowledge, this is the first systematic review on the association of cannabis potency and mental health and addiction.

“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.

"Higher potency cannabis use has also been associated with an earlier onset of psychosis, more symptoms of psychosis, and an increased risk of relapse." 

It said use of higher potency cannabis has been consistently associated with an increased risk of cannabis use disorder (CUD). It said there was “some evidence” to suggest it could be associated with anxiety but said there was “little evidence” linking it with depression. 

The research said studies of people who use medical cannabis found “varied results” and said “findings are difficult to interpret”. It said frequency of use and amount used were typically not factored into studies.

The research concluded: “The findings support recommendations to discourage the use of higher potency cannabis products for low risk use. Policy makers should carefully consider cannabis potency when regulating cannabis in legal markets, such as through limits or taxes based on THC concentration.” 

Commenting, Dr Smyth said: “This paper finds that higher potency cannabis is more strongly associated with psychotic outcomes than lower potency cannabis. It also finds that use of higher potency products is associated with greater risk of addiction. These findings are not a surprise to me.” 

He said cannabis-related harm has “risen massively” in Ireland over the last 15 years. He said this seemed to be explained by “the increase in potency along with increased intensity of use” as the actual numbers of people smoking cannabis had not increased substantially.

Dr Smyth, a Consultant Child & Adolescent Psychiatrist at HSE Adolescent Addiction Services, said one person was admitted to hospital in Ireland every seven hours with a cannabis-related diagnosis, including admissions to medical hospitals and psychiatric hospitals. Dr Smyth said: 

In my clinical work in adolescent addiction services, I witness on a weekly basis the destructive impact which cannabis is having on young lives. 

"While very visible to those of us who work in this clinical area across Ireland, wider society seems blind to this epidemic. The general public appears to have very poor understanding of this increased risk associated with modern cannabis.” 

Dr McGovern, medical director at Priority Medical Clinic, said there has been a big debate as to whether cannabis can cause psychosis or the other way around — that people who are psychotic are more likely to choose cannabis.

“I don’t know what the answer to that is," he said. "I would concede that cannabis, and in higher strengths, probably can trigger a psychotic episode. I treat people with cannabis problems, I treat people who do become psychotic.” 

But he said this begs the bigger question: “If people are coming to harm, what do we do about that and what do we do in terms of the law?” 

He said the debate had become very polarised and that it was very difficult to get impartial assessments of what the impact of regulation in the US and Canada has been. He said: 

If you concede regulation is not great in places where it has been made legal, I would argue you need to regulate it properly, to try and regulate it to the extent that people don’t come to harm. 

He said the wider debate was “going nowhere” and urged the establishment of a time-fixed period within which the issue was thoroughly researched and properly evaluated. 

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