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Genetic predisposition favors cannabis use in people with ADHD

Wednesday, 16 January, 2019

People with ADHD are almost eight times more likely to use cannabis throughout their lives. The study has described four shared genetic regions in both disorders. The prevalence rate of substance use disorder in adult ADHD is 45%.

An international study, led by the team of Psychiatry, Mental Health and Addiction of the Vall d'Hebron Institute of Research (VHIR), research group also belonging to the Center for Biomedical Research in Mental Health Network (CIBERSAM), has been, for the first time, confirmed that people with Attention-Deficit/Hyperactivity Disorder (ADHD) is associated with a significantly increased risk for substance use, abuse and dependence. The study found support that ADHD people lifetime cannabis use is higher than in individuals without ADHD, with an odds ratio 7.9 higher. Specifically, the study has focused on the analysis of the complete genome of more than 85,000 participants. With that large genome-wide associate study have been able to identified four new shared genetic regions between ADHD and substance use. That finding allows to stablish a causal links between these two conditions. The work has been published in the journal Molecular Psychiatry and awarded at the Annual Congress of the European Network for Hyperactivity Disorder on ADHD.

ADHD and cannabis use have a highly complex etiology, which implies a combination of genetic and environmental risk factors. Different studies conducted with twins find out that 75% of ADHD, and 40% to 50% of cannabis use are explained by genetic factors.

In addition, longitudinal and cross-sectional studies show that a diagnosis of ADHD refers to a risk of abuse and substance dependence in adolescents and adults, regardless of the existence of another psychiatric disorder. In fact, the prevalence of substance use is 45% among adults with ADHD, but until now the factors that determine this relationship are unknown.

The present study, fruit of the collaboration between multiple European and American research groups, analyzed the genetic correlation between ADHD and cannabis use throughout life. Authors show evidence of the existence of a genetic overlap of the two traits, where ADHD people have a greater genetic predisposition to cannabis use compared to people without ADHD.

Regarding the applicability of these results, Dr. Marta Ribasés, principal investigator of the Psychiatry, Mental Health and Addictions group at VHIR, highlights "these results corroborate the temporal relationship between ADHD and cannabis use in the future, reinforcing the need for cannabis care in the context of ADHD in medical care, and the need that future genetic studies will bring information on the biological mechanisms underlying both conditions."

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