High-potency Cannabis Use Linked to Increased Risk of Psychosis and Use Disorders, Study Finds

High-potency cannabis use is associated with an increased risk of experiencing psychosis and cannabis use disorder (CUD) compared to low-potency products, according to the first systematic review on the topic.

Published in the Lancet Psychiatry, the researchers from the Addiction and Mental Health Group at the University of Bath, England, say that this finding could help to explain why more people have been receiving treatment for problematic cannabis use in recent years; previous research from the same group also found a significant increase in the concentration of THC in cannabis products over the past half-century.

The researchers also recommend that, in light of these findings on CUD and psychosis, regions with legal access to cannabis should implement strategies to make sure that consumers have access to lower potency products and are provided with accurate information on the content of their products.

Exposure to potent products associated with poorer mental health

The new systematic review searched three comprehensive literature databases for real-world studies relating to cannabis potency and mental health or addiction-related terms.

The researchers identified 20 studies with a total of 119,581 participants for review. Eight of these were investigating psychosis or psychosis-like symptoms, a further eight investigated anxiety, seven investigated depression, and a final six studies investigated CUD.

These studies indicated that users of high-potency cannabis products were at an increased risk of psychosis compared to those who only used low-potency products. The use of high-potency cannabis products was also associated with an earlier age of onset for psychotic disorders compared to low-potency users; after adjusting for gender and frequency of product use, psychosis onset happened approximately four years earlier for the high-potency users.

Notably, another study found that low-potency product users did not appear to be at an increased risk of developing psychosis compared to non-users.

The cross-sectional studies on CUD suggested that high-potency product users are more likely to report cannabis dependence – and report a greater severity of dependence – than people who use exclusively lower potency products. High-potency users were also more likely to report generally experiencing problems related to their cannabis use.

“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,” lead author Kat Petrilli said in a statement.

“These results are important in the context of harm reduction which aims to minimize 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.”

Association less clear for anxiety and depression

For anxiety, study findings were more mixed. One study found that there was no difference in anxiety diagnoses between high-potency and low-potency herbal cannabis users, but that users of high-potency butane hash oil (BHO) may be more likely to have anxiety. However, another study concluded that the use of high-potency cannabis was associated with a two-times greater risk of developing generalized anxiety disorder. All but one of the studies on depression found no association with high-potency products.

This trend – that high potency products may affect anxiety but not depression – has been identified previously. This observation could also help to clarify the nature of the relationship between cannabis and mental health.

“When we do research into cannabis and mental health, people suggest that what we’re seeing is a kind of artifact of self-medication – that people use the drug to attenuate their own mental health symptoms,” review author Dr Lindsey Hines, a researcher at the University of Bristol, previously told Analytical Cannabis following the publication of a previous cohort study investigating high-potency cannabis and mental health.

“And I think the fact that we see an association with anxiety but not depression is kind of an argument against that in this case. Because, anecdotally, people use cannabis to help deal with their anxiety and depression […] So the fact that we’re only seeing this for anxiety supports the case that this is less likely to be self-medication,” Hines explained.

Researchers support recommendation to discourage high-potency cannabis use

The review authors note several limitations with this work. Firstly, many of the studies were ranked as “poor” when subjected to a standard risk of bias test, due to issues with accounting for self-reported cannabis use and the absence of standardized measures for THC exposure. Other factors such as the different definitions of “high potency” products between studies were also of concern. Also, the nature of cross-sectional studies means that the direction of association between cannabis potency and poor mental health cannot be concretely determined.

The scope of this review also only focused on differing THC levels when considering potency, and did not include studies looking at other cannabinoids, such as CBD. It has been suggested that high doses of CBD may help to alleviate cannabis dependency, and so this would be an interesting extra dimension of study.

“We know that CBD has contrasting effects to THC on the endocannabinoid system,” Dr Tom Freeman, an addiction researcher at the University of Bath and author of both the new systematic review and previous research into CBD and cannabis dependence, previously told Analytical Cannabis. “We know that THC is a partial agonist at cannabinoid receptors. But CBD has minimal direct activity at cannabinoid receptors.”

“At the same time, it does have properties that could be helpful in treating cannabis use disorder, such as inhibiting the effects of other ligands acting on the CB1 receptor and increasing endocannabinoids. And this is a potential mechanism through which it could be acting to alleviate the cannabis use disorder and help people cut down their use.”

The systematic review authors include several recommendations for further study. For example, they advise that studies should report models both with and without adjustments for cannabis use frequency and the amount of cannabis used. This could help in terms of understanding whether these are confounders or mediators of the associations that have already been seen.

The researchers also say that their findings support recommendations to discourage the use of high-potency products, and that this recommendation should be incorporated into education tools and considered by policy makers.

“Our findings suggest that people who use cannabis could reduce their risk of harm by using lower potency products,” Freeman said in a statement. “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.”