Summary: A systematic review of nearly 100 studies found that high-THC cannabis products are linked to negative mental health outcomes, particularly psychosis, schizophrenia, and cannabis use disorder. While some therapeutic research hinted at benefits for anxiety and depression, results were inconsistent and often showed potential harm.

The evidence suggests higher THC concentrations carry greater risks, reinforcing concerns about high-potency cannabis use. Researchers emphasize that stronger, better-designed studies are essential to give clearer guidance to patients and healthcare providers.

Key Facts

• Psychosis Risk: High-THC cannabis is strongly associated with psychosis, schizophrenia, and cannabis use disorder.
• Mixed Findings: Some studies suggest potential therapeutic benefit for anxiety and depression, but many show harm.
• Evidence Gap: Current research lacks definitive answers, highlighting the need for improved study design.

Source: American College of Physicians

A systematic review analyzed associations of high-concentration delta-9-tetrahydrocannabinol (THC) cannabis products with mental health outcomes.

The review found that high-concentration THC products are associated with unfavorable mental health outcomes, particularly for psychosis or schizophrenia and cannabis use disorder (CUD).

However, there are limitations to currently available evidence and the researchers call for studies with improved designs to provide more accurate guidance for clinicians and the public.

The review is published in Annals of Internal Medicine.  

Researchers from University of Colorado Anschutz Medical Campus and colleagues analyzed 99 studies comprising 221,097 participants completed between 1977 and 2023.

Study selection was intentionally broad and included studies examining associations between high-concentration cannabis products and mental health outcomes regardless of whether the study had the purpose of evaluating therapeutic effects.

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.

About this psychosis and THC research news

Author: Angela Collom
Source: American College of Physicians
Contact: Angela Collom – American College of Physicians
Image: The image is credited to Neuroscience News

Original Research: Closed access.
“High-Concentration Delta-9-Tetrahydrocannabinol Cannabis Products and Mental Health Outcomes: A Systematic Review” by Jonathan M. Samet et al. Annals of Internal Medicine

Abstract

High-Concentration Delta-9-Tetrahydrocannabinol Cannabis Products and Mental Health Outcomes: A Systematic Review

Background:

Rapid changes in the legalized cannabis market have led to the predominance of high-concentration delta-9-tetrahydrocannabinol (THC) cannabis products.

Purpose:

To systematically review associations of high-concentration THC cannabis products with mental health outcomes.

Data Sources:

Ovid MEDLINE through May 2025; EMBASE, Allied and Complementary Medicine Database, Cochrane Library, Database of Abstracts of Reviews of Effects, CINAHL, and Toxicology Literature Online through August 2024.

Study Selection:

Two reviewers independently selected studies with high-concentration THC defined as greater than 5 mg or greater than 10% THC per serving or labeled as “high-potency concentrate,” “shatter,” or “dab.”

Data Extraction:

Outcomes included anxiety, depression, psychosis or schizophrenia, and cannabis use disorder (CUD). Results were categorized by association direction and by study characteristics. Therapeutic studies were defined by use of cannabis to treat medical conditions or symptoms.

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 or high risk of bias.

In studies not testing for therapeutic effects, high-concentration THC products showed consistent unfavorable associations with psychosis or schizophrenia (70%) and CUD (75%). No therapeutic studies reported favorable results for psychosis or schizophrenia.

For anxiety and depression, 53% and 41% of nontherapeutic studies, respectively, reported unfavorable associations, especially among healthy populations. Among therapeutic studies, nearly half found benefits for anxiety (47%) and depression (48%), although some also found unfavorable associations (24% and 30%, respectively).

Limitation:

Moderate and high risk of bias of individual studies and limited evaluation of contemporary products.

Conclusion:

High-concentration THC products are associated with unfavorable mental health outcomes, particularly for psychosis or schizophrenia and CUD. There was some low-quality evidence, inconsistent by population, for therapeutic benefits for anxiety and depression.

Primary Funding Source:

Colorado General Assembly, House Bill 21-1317.