Cannabis, the most widely used illicit drug globally according to the United Nations Office on Drugs and Crime (UNODC, 2023), is expected to become even more prevalent with the expansion of legal cannabis markets worldwide. Over the past 50 years, the THC content in cannabis has significantly increased (Freeman et al., 2021), potentially leading to more severe health consequences (Petrilli et al., 2021). As noted by former US President Joe Biden, the comparison between old and modern-day cannabis is like contrasting a buckshot in a shotgun shell to a laser-guided missile (Vice, 2019).
With the rise in access to stronger and potentially more harmful cannabis products, it is crucial to understand the associated health risks. Despite cannabis being around for centuries, our understanding of its harms remains limited. Psychiatric conditions are frequently reported among cannabis users (Petrilli et al., 2021), but determining the causal relationship between cannabis use and mental health conditions can be challenging.
Various approaches, such as genetic studies and long-term follow-ups, have been used to tackle this dilemma. The strongest evidence points to an association between cannabis use and psychotic disorders as well as cannabis use disorder (CUD) (Petrilli et al., 2021). However, research on the relationship between cannabis and affective disorders, which are among the most common mental health conditions globally, has been scarce.
Recently, researchers from Denmark, Australia, and the US conducted a study utilizing extensive national Danish register data to investigate the link between CUD and subsequent diagnoses of unipolar depression or bipolar disorder (Jefsen et al., 2023). This study included data from all permanent residents in Denmark since 1968, providing robust and comprehensive information.
Results from the study revealed that individuals with a history of CUD were at a higher risk of developing unipolar depression and bipolar disorder. This risk was most significant in the first six months after a CUD diagnosis but remained elevated over a long period. The study’s strengths include its large sample size and longitudinal design, providing valuable insights into the progression of mental health disorders in individuals with CUD.
However, there are limitations to consider, such as the study’s focus on treatment-seeking individuals and the unique characteristics of the Danish population. The findings may not be directly generalizable to other populations or countries with different healthcare systems and cannabis regulations.
In conclusion, these findings underscore the importance of early intervention and integrated treatment approaches for individuals with CUD and comorbid affective disorders. As cannabis policies evolve, initiatives to prevent cannabis use and mitigate its harmful effects, particularly among young people, are crucial. Effective communication of harm reduction strategies, delay in cannabis use initiation, and reducing the consumption of high-potency products are essential in minimizing the risks associated with cannabis use.
