Cannabis products with high concentrations of delta-9-tetrahydrocannabinol (THC) are associated with users developing cannabis use disorder (CUD) and schizophrenia, according to a new systematic review published in Annals of Internal Medicine.
Researchers reviewed the effects of highly concentrated products containing at least 5 mg THC or more than 10% of the chemical per serving. High-concentration THC products were positively associated with people developing psychosis or schizophrenia (70%) and CUD (75%) in studies that did not investigate the potential of the drug for treatment of medical conditions.
The findings are concerning and warrant a precautionary approach to using cannabis products, particularly for those with preexisting psychosis according to the authors of the peer-reviewed study.
THC concentrations in cannabis have risen in recent decades, up to 80% THC in the form shatter and dabs. The appearance of shatter is similar to peanut brittle, but it is translucent and made by using a solvent such as butane to extract high-potency cannabinoids from the plant’s buds. Dabs are made using a similar method but are waxier in texture. Both are heated, and the vapor is inhaled, or pieces can be rolled into joints.
Because cannabis is a natural substance, there is a general understanding by many that cannabis is beneficial and devoid of adverse outcomes. The findings of this study argue against that conclusion.
In the study, Samet and his associates meta-reviewed the findings of 99 studies that resulted in multiple associations with various mental health disorders. Associations were categorized as favorable (beneficial effects on health), unfavorable (harmful effects on health), null (no difference), or unclear. They included randomized trials (42%), observational studies (47%), and interventional studies (11%).
Nearly two thirds (61%) of studies included participants aged 18-59, with 4% including adolescents. Ethnicity and gender information were not collected.
High-potency THC products were associated with participants developing CUD in 75% of associations. The association with psychosis or schizophrenia was identified during the first 12 hours of use and was present at follow-up of up to 2 months.
High concentrations of THC may acclimate users to higher and higher doses, leading to addiction according to the Centers for Disease Control.
The Samet study found mixed results regarding anxiety and depression. In non-therapeutic studies not measuring effects of products on anxiety or pain, studies participants experienced worsening anxiety in 53% of the associations and depression in 41% of the associations. Healthy participants — those with no co-morbid conditions — were the most prone to these effects.
In therapeutic studies, patients experienced relief from anxiety and depression in half of the associations. Those with cancer and neurologic conditions experienced the most benefits for anxiety.
However, there is no conclusive evidence or scientific consensus that cannabis successfully treats anxiety because there is much data linking cannabis to worsening anxiety.
As of 2024, about 22% of American adults aged 12 or older used cannabis, up from 19% in 2021. With legalization, their recreational frequency of use will increase, and so will psychiatric illness.
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