The Hidden Psychiatric Risks of THC: What the Research Shows
Cannabis use is increasingly common in the United States and Canada. Many people report short-term relief from anxiety, stress, or difficulty sleeping. However, the scientific literature strongly demonstrates that THC can increase the risk of psychosis, worsen impulsivity and emotional dysregulation, increase the likelihood of developing Schizophrenia and Bipolar Disorder, and interfere with normal brain development. These risks are most significant in vulnerable individuals and in people under age 25.
This blog post summarizes the key findings from recent peer-reviewed studies and population-level research.
1. What THC Does in the Brain
THC binds to CB1 receptors located in brain regions responsible for emotional stability, impulse control, motivation, and memory. These include the prefrontal cortex, amygdala, hippocampus, and striatum. Neuroimaging studies find that THC:
Reduces prefrontal cortex activation and blood flow, which impairs executive functioning and emotional regulation (Wesley et al., 2016).
Decreases gray matter density and hippocampal volume in chronic users (Wesley et al., 2016).
Alters orbitofrontal cortex and anterior cingulate activity involved in inhibitory control and decision-making (Figueiredo et al., 2023).
Modifies genes involved in inflammation, mitochondrial function, cytoskeletal processes, and neural development. Several of these biological pathways also appear in Bipolar Disorder (Schierenbeck et al., 2023).
A 2025 MRI study published in JAMA Psychiatry demonstrated that cannabis use disorder is associated with increased dopamine activity in midbrain regions that are also implicated in psychosis. This effect was present even in individuals without schizophrenia (Ahrens et al., 2025). These findings support a clear mechanistic link between THC and psychosis risk.
2. Emotional Dysregulation and THC
Some individuals report experiencing calmness after consuming THC. This effect is real, but the long-term consequences differ significantly from the short-term experience.
Daily-life studies reveal that THC:
Increases hostility and negative emotions on the same day of use, even among recreational users without dependence (Lawn et al., 2023).
Increases next-day impulsivity even after accounting for alcohol use (Lawn et al., 2023).
Is associated with lower self-control and decreased conscientiousness in chronic users (Inzlicht et al., 2024).
Impairs brain regions responsible for emotion regulation and inhibition (Figueiredo et al., 2023).
Although THC may temporarily dampen emotional activation, long-term use reduces distress tolerance and results in greater emotional reactivity.
3. Psychosis Risk, Delusional Thinking, and Hallucinations
A large body of evidence indicates that THC increases the risk of psychosis. Findings from multiple study designs are consistent.
Meta-analyses and case-control data
A major meta-analysis found that heavy cannabis users had 3.9 times greater odds of developing psychosis compared to non-users. The risk increased in a dose-response pattern (Marconi et al., 2016).
The multinational EU-GEI study reported that daily cannabis use increased the odds of first-episode psychosis by 3.2 times, and daily high-potency use increased odds by 4.8 times (Di Forti et al., 2019).
Population attributable fractions from that study suggested that eliminating high-potency cannabis could reduce first-episode psychosis incidence by up to 30 percent in London and 50 percent in Amsterdam (Di Forti et al., 2019).
Population-level outcomes
A 2025 Canadian population analysis found that the proportion of schizophrenia cases attributable to cannabis use disorder more than doubled after legalization. The highest risk increase occurred in males ages 19 to 24 (Myran et al., 2025).
Genetic vulnerability
UK Biobank data show a strong dose-dependent relationship between cannabis use and psychotic experiences including persecutory delusions. The association was significantly stronger among individuals with high polygenic risk scores for schizophrenia (Wainberg et al., 2021).
Longitudinal evidence
Large longitudinal studies in Sweden, New Zealand, Germany, and the Netherlands demonstrate that cannabis use precedes psychotic symptoms and that risk increases with frequency of use. These studies controlled for baseline symptoms and other substances, which strengthens causal interpretation (Hall & Degenhardt, 2008).
Overall, the evidence supports THC as a contributing causal factor for psychosis in vulnerable individuals.
4. Bipolar Disorder and THC
Cannabis use is associated with the development and worsening of Bipolar Disorder. Research shows that:
Cannabis users have an increased risk of manic symptoms and are more likely to develop Bipolar Disorder over time (Schierenbeck et al., 2023).
THC alters cellular pathways related to inflammation, mitochondrial functioning, cytoskeletal integrity, and neural development. Many of these pathways overlap with biological abnormalities found in Bipolar Disorder (Schierenbeck et al., 2023).
Cannabis use is associated with more severe episodes, increased hospitalizations, and poorer long-term functional outcomes in patients with Bipolar Disorder (Schierenbeck et al., 2023).
This suggests that THC interacts with core biological systems disrupted in mood disorders.
5. THC, Impulsivity, and Self-Regulation
THC impairs brain systems responsible for impulse control. Neuroimaging studies demonstrate:
Reduced prefrontal blood flow during tasks requiring inhibition or decision-making (Figueiredo et al., 2023).
Decreased white matter integrity in tracts that support attention and motor inhibition (Wesley et al., 2016).
Daily-life data confirm that:
Cannabis use increases next-day impulsive behavior (Lawn et al., 2023).
Chronic users display lower trait self-control and reduced conscientiousness (Inzlicht et al., 2024).
Individuals with ADHD, borderline personality traits, trauma-related dysregulation, or impulsivity vulnerabilities may be at particularly high risk for negative outcomes.
6. Adolescent THC Use and Neurodevelopment
Brain development continues until approximately age 25. THC has a disproportionate impact on the developing brain.
Research shows that adolescent THC exposure:
Reduces white matter development and disrupts neural connectivity (Wesley et al., 2016).
Interferes with synaptic pruning and dopamine signaling.
Is associated with long-term impairments in memory, attention, and executive functioning (Wesley et al., 2016).
Adolescent THC use significantly increases risk for psychosis, Bipolar Disorder, depression, anxiety, and poor educational or occupational outcomes.
Leaf Psychiatry’s Clinical Position on THC
THC is absolutely contraindicated for individuals under age 25.
Adolescent and young adult brains are more vulnerable to the neurodevelopmental effects of THC. Recreational or self-medicated use is not considered safe for this age group.
THC should be avoided in individuals with:
Psychotic disorders including Schizophrenia
Bipolar Disorder
Emotional dysregulation
Borderline personality traits
ADHD or impulse-control disorders
A family history of schizophrenia or Bipolar Disorder
Leaf Psychiatry does not encourage substance use.
There is no psychiatric disorder for which THC is a first-line or recommended treatment. Evidence-based therapies and medications are safer and more effective alternatives.
Carter Doyle, MSN, PMHNP-BC, is a board-certified psychiatric–mental health nurse practitioner and the founder of Leaf Psychiatry, a trauma-informed practice based in Michigan. Carter specializes in integrative, evidence-based treatment for trauma, mood disorders, and complex emotional dysregulation, drawing on advanced training in Internal Family Systems (IFS), EMDR, and psychometric assessment. He is currently completing his PhD in Nursing at Wayne State University, where his research focuses on trauma, neurobiology, and mental health outcomes. Carter is committed to providing compassionate, scientifically grounded care that promotes long-term healing and resilience.
References
Ahrens, J., Ford, S. D., Schaefer, B., Reese, D., Khan, A. R., Tibbo, P., Rabin, R., Cassidy, C. M., & Palaniyappan, L. (2025). Convergence of cannabis and psychosis on the dopamine system. JAMA Psychiatry, 82(6), 609–617. https://doi.org/10.1001/jamapsychiatry.2025.0432
Ansell, E. B., Laws, H. B., Roche, M. J., & Sinha, R. (2015). Effects of marijuana use on impulsivity and hostility in daily life. Drug and Alcohol Dependence, 148, 136–142.
Delgado-Sequera, A., Garcia-Mompo, C., Gonzalez-Pinto, A., Hidalgo-Figueroa, M., & Berrocoso, E. (2024). A systematic review of the molecular and cellular alterations induced by cannabis that may serve as risk factors for bipolar disorder. International Journal of Neuropsychopharmacology, 27(2), 1–13. https://doi.org/10.1093/ijnp/pyae002
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