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Mood disorders , such as major depressive disorder (MDD) and bipolar disorder (BD), affect a significant portion of the global population, with MDD alone impacting around 300 million individuals worldwide. These disorders typically start in adolescence and can lead to severe functional impairment, impacting quality of life. At the same time, cannabis use is becoming more prevalent globally, with estimates of 192 million users in 2018 and around 3% experiencing cannabis use disorder (CUD). Importantly, rates of cannabis use among those with mood disorders are increasing, with individuals with MDD showing a 216% increase in daily cannabis use between 2015 and 2016 compared to non-depressed individuals.
The compounds in cannabis, including delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), affect the endocannabinoid system, which plays a role in brain development and emotion regulation. THC is known for its psychotomimetic effects, while CBD is believed to have antipsychotic and anti-anxiety properties. The relationship between cannabis use and mood disorders is complex, with evidence suggesting both relief of depressive symptoms during acute use and exacerbation of symptoms with long-term or heavy use.
Research on cannabis use and mood disorders has produced inconsistent results, with some studies showing no association between cannabis use and MDD or BD, while others demonstrate a positive relationship. This review aims to comprehensively evaluate studies investigating the relationship between cannabis use, CUD, and mood disorders, as well as the effects of cannabis on treatment outcomes, cognition, and neural functioning in individuals with MDD and BD.
This systematic review comprehensively assesses how cannabis use affects the development of mood disorders, with a focus on Major Depressive Disorder (MDD) and Bipolar Disorder (BD). It also explores the impact of cannabis on prognosis and treatment outcomes for individuals with MDD or BD. The findings suggest that cannabis use is linked to increased depressive and manic symptoms in the general population, as well as a higher risk of developing MDD and BD. However, there’s limited evidence supporting cannabis as beneficial for clinical or treatment outcomes in MDD or BD; instead, it’s associated with worse prognosis for both disorders. Unlike previous reviews, this study looks at associations between cannabis use and mood symptoms across various populations, and it delves into multiple outcomes, including cognition and neural functioning, in MDD and BD. Despite examining the potential therapeutic effects of cannabinoids, only one trial met the criteria. This expanded analysis provides a more comprehensive understanding of the complex relationship between cannabis use and mood-related outcomes.
We discovered a link between cannabis use and increased depressive symptoms, mania, and suicidality. There’s evidence showing that the longer someone uses cannabis, especially if they start during adolescence, the more likely they are to experience depression and mania. This is crucial because adolescence is a time of significant brain development, making young people more vulnerable to the effects of substances like THC. Studies have found abnormalities in brain regions with a lot of CB1 receptors among cannabis users. However, we also found that the connection between cannabis and mood disorders can be affected by other factors like using other substances simultaneously. Since many cannabis users also use other substances, it’s important to consider their impact on brain development and mood when studying the relationship between cannabis and mood disorders.
In major depressive disorder (MDD), cannabis use and cannabis use disorder (CUD) are associated with more severe symptoms and a less favorable prognosis compared to non-users. These include increased anhedonia, suicidality, reduced treatment adherence, and poorer cognition. However, a study showed significant improvements in cognition and depressive symptoms after 28 days of cannabis abstinence, suggesting that the negative effects may be reversible. Yet, this study lacked a non-abstinent control group, highlighting the need for more controlled, long-term research in this area. Interestingly, some data suggests that those with MDD who use cannabis may have better cognitive functioning compared to non-users, emphasizing the necessity for further controlled studies.
In bipolar disorder (BD), cannabis use leads to more severe symptom profiles, more frequent manic and depressive episodes, rapid cycling, and higher levels of suicidality. Despite these negative outcomes, some studies suggest that immediate mood improvements are experienced by cannabis users with BD. There’s also evidence indicating that individuals with baseline manic or depressive symptoms are more likely to initiate cannabis use, emphasizing the importance of further investigation into this association. Clinicians and researchers need to explore evidence-based alternatives for mood disorder management.
Therapeutically, there’s limited evidence supporting cannabinoids in mood disorders. A randomized controlled trial (RCT) on CBD for BD showed inconclusive results, although CBD may be a safe option. Studies on other cannabinoids like dronabinol and nabilone have focused on conditions like chronic pain disorders, with some evidence of mood and anxiety symptom improvement. However, more research, particularly in clinical populations with established mood disorders, is needed to determine the efficacy and safety of cannabinoids.
This systematic review has strengths in its comprehensive coverage of various study types and outcomes related to cannabis use and mood disorders. It examined cross-sectional and prospective studies, offering a holistic view of the evidence. Multiple dimensions were explored, including depressive and manic symptoms, diagnostic outcomes, cognition, neuroimaging, and treatment outcomes, providing a thorough assessment.
However, limitations include the heterogeneity among studies in methodology, outcome measures, and participant characteristics. Variability in measurements of cannabis use, often relying on self-reports, and lack of standardized assessments impact findings. Few studies investigated variables like potency and route of administration in relation to outcomes, with mixed findings. Observational studies dominate, limiting establishing causality, and few controlled for important confounding factors. Additionally, gender-specific analyses were lacking, despite known gender differences in cannabis effects, highlighting the need for more inclusive research.
Cannabis use is associated with increased depressive and manic symptoms and a higher risk of major depressive disorder (MDD) and bipolar disorder (BD) in the general population. Evidence suggests cannabis-related harms in mood disorders. Mental health practitioners should include cannabis screening in assessments for mood disorders, informing patients of associated risks. Clinicians should explore evidence-based alternatives for mood symptom management instead of cannabis. Policymakers should consider targeted interventions and educational programs about cannabis risks, especially for those with mood disorders.
Further research into the neurobiological mechanisms and causal links between cannabis use and mood disorders, both in humans and animals, is necessary for a better understanding. Well-controlled prospective studies, including sex- and gender-specific analyses, are needed to deepen our understanding of this relationship. These efforts will enhance our knowledge and benefit those affected by mood disorders.
Source:
Sorkhou, M., Dent, E. L., & George, T. P. (2024). Cannabis use and mood disorders: a systematic review. Frontiers in public health, 12, 1346207. https://doi.org/10.3389/fpubh.2024.1346207