High-potency cannabis use is associated with an increased risk of addiction – mental health problems

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As the strength or potency of cannabis products has increased internationally over the years, so have rates of people being treated for cannabis addiction, say the authors of a new study.

Researchers from the Addiction and Mental Health Group at the University of Bath (UK) systematically analysed the relationship between the types of cannabis people use and their addiction and mental health problems. Their work draws on 20 studies involving almost 120,000 people.

After alcohol and nicotine, cannabis is the most widely used drug globally. Latest estimates from the UK suggest that over the last year around one in five 16-24 year olds had used cannabis.

Cannabis potency refers to the concentration of tetrahydrocannabinol (THC) in cannabis – the key psychoactive drug it contains. Recent studies from the same team at Bath have found that the concentration of THC in cannabis has increased significantly over time meaning that cannabis used today is typically much stronger than previously.

The new study, published in The Lancet Psychiatry, suggests that people who use high potency cannabis are more likely to experience addiction than those using low potency products. It also suggests that people using high potency cannabis are more likely to experience a psychotic disorder, such as schizophrenia.

These findings may help to explain why more people have received treatment for cannabis problems over recent years. Data from the European Monitoring Centre for Drugs and Drug Addiction show a 76% increase in people entering treatment for cannabis addiction in the past decade.

Based on these new results, the authors argue that public health guidelines and policies to help make cannabis use safer should be encouraged.

Lead author, Kat Petrilli from the University of Bath’s Department of Psychology explained: “Our systematic review found that people who use higher potency cannabis could be at increased risks of addiction as well as psychosis when compared to people who use cannabis products with lower potencies.

“These results are important in the context of harm reduction which aims to minimise the negative consequences associated with drug use. While the safest level of use for cannabis is of course ‘no use’, it is important to acknowledge that a significant number of people across the world use cannabis regularly and to ensure they can make informed decisions that could reduce any possible harms associated with it.”

The authors point out that strategies to make cannabis use safer could inform how the drug is regulated in the UK and internationally. Recreational cannabis use remains illegal in the UK, but cannabis products are now legally sold for recreational use in Canada, Uruguay, and parts of the USA.

Several other countries appear set to follow this trend, including Germany. In the UK, the Liberal Democrats have argued that a legal regulated market could make cannabis use safer by enforcing a limit on the potency of cannabis products, and investing the revenue and savings from this into education and treatment for cannabis problems.

Senior author, Dr Tom Freeman explained: “Our findings suggest that people who use cannabis could reduce their risk of harm by using lower potency products. In places where cannabis is legally sold, providing consumers with accurate information on product content and access to lower potency products could help people to use cannabis more safely.”

Despite anecdotal evidence of links between cannabis and anxiety and depression, the authors note that the links between cannabis potency and other mental health problems are unclear.


The present study restricts analyses to individuals who have used different forms of cannabis to inform understanding of the implications of the proliferation of high-potency cannabis in legal markets.4,5 In a general population sample of young people in the UK, individuals who use high-potency cannabis (compared with those using lower-potency forms of cannabis) are more likely to be using cannabis regularly, more likely to report having recently experienced problems associated with their cannabis use, and more likely to concurrently be experiencing use of other illicit drugs, tobacco dependence, AUD, generalized anxiety disorder, and PEs.

After adjustment for age at onset of cannabis use or for early adolescent measures of psychopathologic conditions and frequency of cannabis use, high-potency cannabis was associated with increases in the likelihood of frequent cannabis use, having recently experienced problems associated with cannabis use, and the likelihood of experiencing generalized anxiety disorder.

The results provide a profile of individuals who use high-potency cannabis, indicating that this behavior is more common among individuals who are male, grow up in families with a low socioeconomic status, experience early PEs, and report early-onset cannabis use.

The outcomes regarding substance use and mental health may reflect shared predisposing risk factors that could also lead people to select the most potent drug available.25 As the sample excluded those who had not used cannabis, increases in risk for mental health outcomes associated with the use of high-potency cannabis are unlikely to be conflated by a shared liability to drug use and mental health disorders.

However, evidence shows that shared risk factors underlie both exposure to cannabis and progression to development of dependence.26 The profile of substance use outcomes and early-life experiences among those who use high-potency cannabis in the present study indicates that there may be overlapping risk factors between development of substance use and mental health disorders and the selection of higher-potency forms of cannabis. We have sought to adjust for these factors, but further consideration of the role of cannabis potency in the causal path to mental health disorders is warranted.

The estimate in the present study for the likelihood of depression among those using high-potency cannabis is similar to estimates observed in a previous study of a self-selecting sample of drug-using participants (OR, 1.18; 95% CI, 1.11-1.25).11 However, the estimate in the present study demonstrating an increase in the likelihood of generalized anxiety disorder among those using high-potency cannabis is in contrast to the negligible increase in likelihood of lifetime anxiety disorder observed in a previous study (OR, 1.05; 95% CI, 0.98-1.12).11

This discrepancy may be because the previous study relied on self-reported lifetime diagnosis,11 whereas the present study used DSM-IV–validated measures of depression and generalized anxiety disorder at the time of assessment. A recent systematic review has indicated that cannabis use in adolescence is associated with an increased likelihood of lifetime depression and anxiety,8 although few studies had considered the potency or frequency of cannabis use.

A better understanding of the association between potency and frequency of cannabis use is required to gain a clearer understanding of the independent association of potency with mental health. We found similar effect sizes for the association between the use of high-potency cannabis and report of frequent or distressing PEs (not associated with drug use) as those observed in case-control studies of first-episode psychosis.9,10 However, in our study, we observed a substantial attenuation in effect size, by approximately 66%, after adjustment for frequency of cannabis use.

The present findings on cannabis problems and frequency of use are consistent with previous evidence for a positive association between days of use of high-potency cannabis and severity of dependence.12 In this previous study there was a linear association between number of days of high-potency cannabis use per month and severity of dependence score (β = 0.15; 95% CI, 0.02-0.28).

Increased frequency of cannabis use could plausibly cause individuals to use higher-potency cannabis through the development of tolerance to the effects of cannabis; if so, then it is appropriate to consider cannabis use frequency as a confounding factor in the association with mental health.

However, if the use of higher-potency cannabis leads to increased frequency of use, plausibly through high-potency cannabis delivering THC more efficiently than lower-potency cannabis, it would be more appropriate to explore the mediating effect of cannabis frequency.

reference link :https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2765973


Original Research: Closed access.
Association of cannabis potency with mental ill health and addiction: a systematic review” by Kat Petrilli et al. Lancet Psychiatry

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