A systematic review has linked high-concentration THC cannabis products to negative mental health outcomes, particularly psychosis, schizophrenia, and cannabis use disorder.
A new systematic review has examined how cannabis products with high levels of delta-9-tetrahydrocannabinol (THC) are linked to mental health outcomes. The analysis revealed that products with elevated THC concentrations are tied to negative effects on mental health, especially when it comes to psychosis, schizophrenia, and cannabis use disorder (CUD).
The authors caution that existing research has important limitations. They stress the need for better-designed studies that can provide clearer and more reliable guidance for both healthcare providers and the general public. The review was published in Annals of Internal Medicine.
The investigation was led by researchers at the University of Colorado Anschutz Medical Campus, along with their collaborators. They evaluated 99 studies involving 221,097 participants conducted between 1977 and 2023. The selection criteria were deliberately wide-ranging, including any studies that assessed connections between high-concentration cannabis use and mental health outcomes, whether or not the original purpose of the research was to test therapeutic effects.
Defining High-Concentration THC
High-concentration cannabis products were defined as having THC concentration exceeding 5 mg THC or 10% THC per serving or products described as “high-potency concentrate,” “shatter,” or “dab.” The mental health outcomes of interest included anxiety, depression, psychosis, schizophrenia, CUD, and other substance use disorders. The researchers defined acute effects (within 12 hours), post-acute effects (after consistent use for 1 to 2 months), and long-term effects (after consistent use for > 1 year).
In studies not testing for therapeutic effects, high-concentration THC products were associated with psychosis, schizophrenia, and cannabis use disorder. No therapeutic studies found favorable effects on psychosis or schizophrenia.
Of non-therapeutic studies, 53% identified unfavorable associations with anxiety and 41% found unfavorable associations with depression. Among therapeutic studies, some suggested beneficial effects for anxiety (47%) and depression (48%), while others suggested unfavorable effects (24% for anxiety and 30% for depression).
The findings reinforce previous conclusions that higher THC concentrations increase the risk for adverse mental health outcomes; however, they fall short of providing the definitive evidence needed to provide clear advice to patients.
Reference: “High-Concentration Delta-9-Tetrahydrocannabinol Cannabis Products and Mental Health Outcomes” by Thanitsara Rittiphairoj, Louis Leslie, Jean-Pierre Oberste, Tsz Wing Yim, Gregory Tung, Lisa Bero, Paula Riggs, Kent Hutchison, Jonathan Samet and Tianjing Li, 25 August 2025, Annals of Internal Medicine.
DOI: 10.7326/ANNALS-24-03819
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