Summary: A systematic review of nearly 100 studies found that high-THC cannabis products are associated with negative mental health effects, particularly psychosis, schizophrenia, and cannabis dependence. While some treatment studies suggested benefits for anxiety and depression, the results were inconsistent and often revealed potential harms.
There are indications that higher concentrations of THC pose greater risks, raising concerns about the use of higher-potency cannabis. The researchers emphasize that more robust and better-designed studies are crucial to provide clear guidelines for patients and healthcare professionals.
Key data
- Risk of psychosis: High-THC cannabis is strongly associated with psychosis, schizophrenia, and cannabis addiction.
- Mixed results: Some studies suggest potential therapeutic effects for anxiety and depression, but many studies also show harmful effects.
- Lack of evidence: Current research does not provide a clear answer, highlighting the need for better research designs.
Source: American College of Physicians
A systematic review examined the association between cannabis products containing high amounts of delta-9-tetrahydrocannabinol (THC) and mental health problems.
Research has found that high-THC products are linked to negative mental health effects, particularly psychosis or schizophrenia, and cannabis use disorder (CUD).
However, there are limitations to the currently available evidence, and researchers are calling for better study designs to provide more accurate guidance to doctors and the public. This review was published in the Annals of Internal Medicine. Researchers at the University of Colorado Anschutz Medical Campus and their colleagues analyzed 99 studies involving 221,097 participants conducted between 1977 and 2023.
The selection of studies was intentionally broad and included studies examining the relationship between potent cannabis products and mental health problems, regardless of whether the study was designed to assess treatment effects.
High-THC cannabis products in the study were classified based on their potency and labeling. Specifically, products containing more than 5 mg of THC or exceeding 10% THC per serving were considered high-potency. Additionally, items marketed with terms such as “high-THC concentrated,” “shatter,” or “dab” also fell into this category. These highly potent cannabis formulations have become increasingly accessible and popular, raising concerns among researchers and healthcare professionals about their potential impact on mental health, especially when consumed frequently or over long periods.
The study highlighted a range of associated mental health issues linked to the use of high-THC cannabis. These included increased risks of anxiety, depression, and psychosis, as well as more severe conditions such as schizophrenia. Beyond diagnosable disorders, the research also pointed to broader cognitive and behavioral challenges, often requiring intervention through cognitive behavioral therapy (CBT). Moreover, a strong correlation was observed between high-THC cannabis use and the development of other substance use disorders, indicating a possible gateway effect or shared vulnerability among users of high-potency cannabis products.
To better understand the progression and duration of these health effects, researchers categorized them into three temporal phases: acute effects (occurring within 12 hours of use), post-acute effects (emerging after 1 to 2 months of continuous use), and long-term effects (developing after more than a year of sustained use). This classification helped illustrate how high-THC cannabis can have both immediate and delayed consequences on mental and cognitive health. By delineating these phases, the study offers a framework for clinicians and public health professionals to assess risk, monitor symptoms, and design targeted interventions based on duration and intensity of cannabis exposure.
In studies that did not investigate therapeutic effects, high-THC products have been linked to psychosis, schizophrenia, and cannabis addiction. No therapeutic treatment has shown positive effects on psychosis or schizophrenia.
Among individuals in non-treatment-seeking groups, a significant portion reported negative mental health associations linked to high-THC cannabis use. Specifically, 53% reported worsened anxiety symptoms, while 41% experienced a decline in mood associated with depression. These findings highlight a concerning trend among casual or recreational users who are not actively seeking mental health support, suggesting that high-THC cannabis may contribute to or exacerbate underlying psychological conditions even in individuals who do not initially perceive a need for clinical intervention.
In contrast, findings from therapy-based studies where cannabis use was incorporated into or examined alongside therapeutic settings revealed more mixed outcomes. Some studies reported positive effects, with 47% of participants showing improvements in anxiety and 48% reporting reduced symptoms of depression. However, these potential benefits were counterbalanced by negative effects observed in 24% of anxiety cases and 30% of depression cases, even within therapeutic contexts. This variation underscores the complex relationship between THC exposure and mental health, which may be influenced by individual factors such as dosage, frequency of use, mental health history, and the therapeutic environment itself.
Overall, the results reinforce previous research indicating that higher THC concentrations are associated with an increased risk of adverse mental health outcomes. However, while the data provide valuable insights, they stop short of offering conclusive evidence necessary to establish definitive clinical guidelines or patient recommendations. The inconsistencies across different populations and study settings point to the need for more controlled, longitudinal research to clarify these relationships. Until such evidence is available, healthcare providers must approach cannabis-related mental health guidance with caution, emphasizing individualized risk assessments and harm reduction strategies.
Abstract
Cannabis products containing high levels of delta-9-tetrahydrocannabinol and their effects on mental health: a systematic review
Background:
Rapid changes in the legal cannabis market have led to a surge in cannabis products containing high concentrations of delta-9-tetrahydrocannabinol (THC).
Objective:
The goal is to systematically investigate the associations between high-THC cannabis products and effects on mental health.
Data sources:
Ovid MEDLINE to May 2025; EMBASE, the Complementary and Allied Medicine Database; Cochrane Library, the database of abstracts of reviews of effects; CINAHL; and the online toxicology literature to August 2024.
Study selection:
Two independent reviewers selected studies with high THC concentrations, defined as more than 5 mg or 10% THC per serving, or described as “high-quality concentrates,” “shutters,” or “dabs.”
Data extraction:
Outcomes included anxiety, depression, psychosis, or schizophrenia, as well as cannabis use disorder (CUD). Outcomes were categorized based on the direction of association and study characteristics. Therapeutic use was defined as the use of cannabis to treat a medical condition or symptom.
Data synthesis:
Ninety-nine studies (221,097 participants) were included: randomized trials (42%), observational studies (47%), and other interventional study designs (11%); more than 95% had moderate to high risk of bias.
In studies that did not investigate the therapeutic effects of high-THC products, a consistent negative association was observed with psychosis or schizophrenia (70%) and substance abuse (75%). No positive treatment outcomes were reported for psychosis or schizophrenia.
Regarding anxiety and depression, 53% and 41% of non-treatment studies, respectively, reported negative associations, mainly in healthy individuals. In treatment studies, about half found benefits for anxiety (47%) and depression (48%), but some also found negative associations (24% and 30%, respectively).
Range:
Moderate to high risk of bias in individual studies and limited evaluation of contemporary products.
Diploma:
Products with high THC concentrations are associated with negative mental health outcomes, particularly psychosis, schizophrenia, and substance abuse. There is moderate to conflicting evidence for their therapeutic benefits for anxiety and depression.
Primary source of funding:
Colorado General Assembly, House Bill 21-1317.
