John Wang, MD, and Deepti Anbarasan, MD. Dr. Wang and Dr. Anbarasan have no financial relationships with companies related to this material.
STUDY TYPE: Literature review
Delta-9-tetrahydrocannabinol (THC, the main psychoactive component of cannabis) is associated with a host of psychiatric issues including addiction and psychosis, as well as possible links to impaired cognition and anxiety. In recent years, the THC concentration in cannabis, frequently referred to as “potency,” has been on the rise (cannabis products are discussed in detail in CATR Sept/Oct 2022). But are these higher-potency formulations associated with a higher risk of mental illness?
Researchers performed a systematic review of research published before January 2021 and included 20 observational studies with over 100,000 total participants. Each study reported on an association between cannabis potency and outcomes relating to psychosis, anxiety, depression, or cannabis use disorder (CUD).
The strongest connection that researchers identified was between high-potency cannabis use and psychosis, especially with daily use. Studies found that users of high-potency cannabis had about a three-fold risk of experiencing first-episode psychosis compared to those who did not use cannabis at all. Daily use of high-potency cannabis increased the risk even more, to around five-fold risk. High-potency cannabis was also associated with an earlier onset of psychotic disorder by approximately four years. People using high-potency cannabis tended to experience more positive symptoms during psychotic episodes relative to non-users and to users of low-potency cannabis. Finally, one study found that daily high-potency cannabis use was associated with increased risk of subsequent psychosis in the two years following a first episode (aOR=3.28, 95% CI 1.22–9.18). Again, low-potency use did not show this association.
Use of high-potency cannabis was also linked to an increased risk of developing CUD, with one study finding that high-potency products were associated with a seven-fold increase of CUD as compared to low-potency products (aOR=6.9, 95% CI 1.19–25.15). Users of high-potency cannabis were also more likely to report problems associated with their use, such as memory problems, inability to reduce use, getting in arguments, or doing poorly in school. Evidence was mixed when it came to anxiety. The authors concluded that high-potency cannabis might be associated with worse anxiety symptoms, but they couldn’t make any definitive conclusions. They failed to find a strong connection between cannabis potency and depression.
The major limitation of this systematic review was heterogeneity between studies. For example, some studies compared users of high-potency and low-potency cannabis products head to head, while others compared both groups to a non-cannabis-using placebo group. There is no standard definition of what constitutes high and low potency, and the studies used varying definitions. For your own practice, it’s good to know the line is around 10% or so. Most of the included studies would classify whole-plant cannabis above 10% THC content as high potency, and certainly any THC concentrate product would also be considered high potency.
Higher-potency cannabis is associated with earlier onset and more symptomatic psychosis, as well as a higher incidence of CUD. While this review does not prove a causal link, the associations reported here are evidence enough to warrant warning your patients against use of high-potency cannabis, especially in those otherwise at risk of psychosis or development of substance use disorder.
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