The ADHD-Cannabis Connection: Genetics, Risks, and Treatment Implications

Details: Published: 24 July 2024; Hits: 162

Attention-Deficit/Hyperactivity Disorder (ADHD) and cannabis use have become increasingly intertwined topics of research in recent years. As the prevalence of both ADHD diagnoses and cannabis use continues to rise, understanding the relationship between these two phenomena has become crucial for healthcare professionals, researchers, and individuals affected by ADHD. This report aims to explore the complex interplay between ADHD and cannabis use, examining genetic factors, potential causal relationships, and the current state of research on cannabis as a potential treatment for ADHD symptoms.

ADHD is a neurodevelopmental disorder characterised by persistent inattention, hyperactivity, and impulsivity. It affects approximately 5% of children and adolescents and 2.5% of adults worldwide. On the other hand, cannabis use has become increasingly prevalent, with many individuals reporting recreational and medicinal use. The intersection of these two areas presents a unique challenge for researchers and clinicians alike, as they attempt to unravel the complexities of their relationship and potential implications for treatment and management of ADHD.

Genetic Overlap between ADHD and Cannabis Use
Recent genome-wide association studies (GWAS) have shed light on the genetic underpinnings of both ADHD and cannabis use. A cross-disorder GWAS reported in Nature Mental Health (2024) identified significant genetic overlap between ADHD, cannabis use disorder (CUD), and cannabis use (CU).
The study identified 36 concordant genome-wide significant loci for ADHD-CUD and ten loci for ADHD-CU. One notable finding was the identification of DRD2 as an ADHD-CUD risk gene. This gene is known to play a role in dopamine signalling, which is implicated in both ADHD and substance use disorders. The discovery of shared genetic loci suggests that there may be common biological pathways underlying both ADHD and cannabis-related behaviours.
Interestingly, the study found that ADHD-CUD risk genes showed high expression across various brain tissues and developmental stages. This pattern was not observed for ADHD-CU genes, indicating that the genetic basis for cannabis use disorder in individuals with ADHD may involve more extensive alterations in brain function compared to cannabis use alone.
These genetic findings provide a foundation for understanding the biological mechanisms that may contribute to the increased prevalence of cannabis use and cannabis use disorder among individuals with ADHD. By identifying specific genes and pathways involved, researchers may be able to develop more targeted interventions and treatments for individuals with comorbid ADHD and cannabis-related issues.

Genetic Correlations and Risk Assessment
The genetic studies have revealed important correlations between ADHD, cannabis use, and other related traits. Both ADHD-CUD and ADHD-CU showed similar genetic correlations with substance use in general. However, they differed in their genetic correlations with substance use disorders, suggesting that the genetic factors contributing to problematic cannabis use in ADHD may be distinct from those involved in casual use.
One of the most striking findings from the genetic research is the potential for using polygenic scores (PGS) to assess the risk of comorbid cannabis use disorder in individuals with ADHD. The study found that individuals with ADHD who had high CUD polygenic scores had a substantially increased risk of developing cannabis use disorder. Specifically, those in the highest CUD-PGS bin had an absolute risk of 22% for comorbid CUD, compared to a risk of only 1.6% among controls.
These findings have significant implications for clinical practice. The ability to stratify individuals with ADHD based on their genetic risk for cannabis use disorder could allow for more personalised prevention and intervention strategies. For example, clinicians could provide targeted education and support to those at highest genetic risk for developing problematic cannabis use.
It’s important to note that there were substantial sex-specific differences in the genetic risk assessment. Men in the highest CUD-PGS bin showed an approximately 10% higher risk of cannabis use disorder compared to women in the same risk category. This underscores the need for sex-specific approaches in both research and clinical interventions related to ADHD and cannabis use.

Causal Relationships between ADHD and Cannabis Use
While genetic overlap provides insight into shared biological mechanisms, it doesn’t necessarily imply a causal relationship between ADHD and cannabis use. To address this question, researchers have employed sophisticated statistical techniques, such as Mendelian randomisation, to infer potential causal links.
A study published in Molecular Psychiatry (2021) used a two-sample Mendelian randomisation approach to investigate the causal relationship between ADHD and lifetime cannabis use. The results provided support for the hypothesis that ADHD is causal for lifetime cannabis use. The study estimated an odds ratio of 7.9 for cannabis use in individuals with ADHD compared to those without ADHD (95% CI: 3.72-15.51, P=5.88×10−5).
This finding is particularly important as it substantiates the temporal relationship between ADHD and future cannabis use. It suggests that individuals with ADHD are at significantly higher risk of engaging in cannabis use later in life, potentially as a form of self-medication or due to impulsivity associated with the disorder.
The causal relationship between ADHD and cannabis use has important implications for clinical interventions and public health strategies. It reinforces the need to consider substance misuse prevention and treatment in the context of ADHD management. Early intervention and targeted support for individuals with ADHD may be crucial in reducing the risk of later cannabis use and associated problems.

Cannabis as a Potential Treatment for ADHD
Despite anecdotal reports from some individuals with ADHD claiming that cannabis helps alleviate their symptoms, the scientific evidence supporting cannabis as a treatment for ADHD is limited and inconclusive. A scoping review published in the Journal of Psychiatric Research (2022) examined the current state of research on this topic.
The review identified only one randomised controlled trial (RCT) that directly measured the effect of cannabis on ADHD symptoms. This study found no significant effect of cannabis on the primary outcome measure, the QbTest (Est = −0.17, 95% CI -0.40 to 0.07, p = 0.16). The lack of well-designed RCTs in this area highlights the need for more rigorous research to evaluate the potential therapeutic effects of cannabis on ADHD symptoms.
While some individuals with ADHD report subjective improvements in their symptoms with cannabis use, the majority of studies included in the review indicated that cannabis either worsened ADHD symptoms or had no effect. This discrepancy between anecdotal reports and empirical evidence underscores the complexity of the relationship between cannabis and ADHD, and the potential for placebo effects or other factors to influence subjective experiences.
One significant limitation in the current research is the lack of standardisation in cannabis preparations used across studies. The concentration and amount of THC (tetrahydrocannabinol) and CBD (cannabidiol) were not well measured in most studies, making it difficult to draw conclusions about the specific effects of different cannabis components on ADHD symptoms.
Neuropsychiatric Effects and Imaging Studies
To better understand the potential impact of cannabis on ADHD, several studies have employed neuropsychiatric tests and neuroimaging techniques. These approaches aim to elucidate the effects of cannabis use on cognitive function and brain structure in individuals with ADHD.
Neuropsychiatric tests have provided mixed results, with some studies suggesting potential cognitive improvements with cannabis use in ADHD, while others indicate detrimental effects or no significant change. The variability in these findings may be due to differences in study designs, cannabis preparations used, and the specific cognitive domains assessed.
Neuroimaging studies have begun to shed light on the structural and functional brain changes associated with cannabis use in individuals with ADHD. Some research has suggested alterations in brain regions involved in attention, impulse control, and reward processing. However, the long-term implications of these changes and their relationship to ADHD symptoms remain unclear.
One area of particular interest is the potential differential effects of THC and CBD on ADHD-related brain function. While THC is known for its psychoactive properties, CBD has been associated with potential neuroprotective and anxiolytic effects. Future research focusing on the isolated effects of CBD on ADHD symptoms and pathophysiology may provide valuable insights into potential therapeutic applications.

Clinical Implications and Future Directions
Given the current state of evidence, cannabis is not recommended as a treatment for ADHD. The potential risks associated with cannabis use, particularly in young people with developing brains, outweigh any potential benefits suggested by anecdotal reports. Clinicians should be aware of the increased risk of cannabis use and cannabis use disorder among individuals with ADHD and incorporate substance use screening and prevention strategies into their ADHD management plans.

Future research in this area should focus on several key areas:

1. Well-designed randomised controlled trials examining the effects of standardised cannabis preparations on ADHD symptoms.
2. Longitudinal studies to better understand the long-term impacts of cannabis use on ADHD symptom progression and overall functioning.
3. Investigation of the potential therapeutic effects of isolated cannabinoids, particularly CBD, on ADHD symptoms.
4. Development and validation of objective measures for both cannabis exposure and ADHD symptom assessment to improve the quality of research in this field.
5. Exploration of sex-specific effects and personalised approaches to ADHD management in the context of cannabis use risk.

As our understanding of the genetic and neurobiological underpinnings of both ADHD and cannabis use continues to grow, there is potential for the development of more targeted interventions. This may include personalised risk assessments based on genetic profiles and tailored prevention strategies for individuals with ADHD who are at high risk for problematic cannabis use.
The relationship between ADHD and cannabis use is complex and multifaceted. Recent genetic studies have revealed significant overlap between the two, suggesting shared biological pathways. While there is evidence for a causal relationship between ADHD and future cannabis use, the efficacy of cannabis as a treatment for ADHD remains unproven and potentially risky. Ultimately, addressing the intersection of ADHD and cannabis use will require a multidisciplinary approach, combining insights from genetics, neuroscience, clinical psychology, and public health.