High Levels of THC in Cannabis Products Associated With Mental Health Risks
Cannabis products that contained high concentrations of delta-9-tetrahydrocannabinol (THC) were associated with psychosis, schizophrenia, and cannabis use disorder (CUD), according to a systematic review published in the Annals of Internal Medicine.
“Currently, cannabis flower in the United States has an average THC concentration of 20%, and concentrations are even higher in states with legalized cannabis,” wrote first author Thanitsara Rittiphairoj, MD, MPH, Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, and coauthors. “The increased availability of cannabis products with substantially higher THC levels than before has raised concerns about associated risks to health.”
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The researchers analyzed 99 studies with a total of 221,097 participants that investigated the relationship between high-concentration THC products (defined as greater than 5 mg or greater than 10% THC per serving or labeled as "high-potency concentrate," "shatter," or "dab”) and mental health outcomes. This included randomized trials (42%), observational studies (47%), and other interventional study designs (11%). Researchers also differentiated between studies that investigated cannabis products for therapeutic and nontherapeutic effects.
The analysis found that studies not testing for therapeutic effects reported consistent unfavorable associations between high-concentration THC products and CUD (75%) and psychosis or schizophrenia (70%). None of the therapeutic studies reported favorable effects on psychosis or schizophrenia.
Of the nontherapeutic studies, 53% and 41% also reported unfavorable associations for anxiety and depression, respectively. This was particularly salient in healthy populations. However, nearly half of the therapeutic studies reported benefits for both depression (48%) and anxiety (47%), with more favorable results for anxiety present in participants with cancer and neurologic conditions. A smaller number of therapeutic studies reported unfavorable associations (30% for depression and 24% for anxiety).
“The findings with regard to anxiety, depression, psychosis or schizophrenia, and CUD are concerning—even among otherwise healthy persons, potentially including those using the products for recreational purposes—albeit not definitive for causation and imply a need for precautionary guidance,” the authors concluded, suggesting future studies “with improved designs are needed to provide sharper guidance for clinicians and the public generally.”
