Does cannabis affect brain development in young people with ADHD? Too early to tell


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At least so far, the currently limited research base does not establish that cannabis has additional adverse effects on brain development or functioning in adolescents or young adults with attention deficit / hyperactivity disorder (ADHD), concludes a review in the issue of July / August of Harvard Review of Psychiatry.

Although ADHD is clinically defined with impaired cognitive functioning, cannabis use alone is also associated with cognitive impairment: “[T]to date, evidence supports neither an addictive effect nor an interaction (either protective or harmful) with cannabis use, “according to the study by Philip B. Cawkwell, MD, of Stanford University School of Medicine , and colleagues: the need for more research to clarify the possible effects of cannabis on brain structure, function and behavior with ADHD.

“Urgent need” for definitive studies on cannabis risk in adolescents with ADHD

Trends toward legalization and increased accessibility and potency of cannabis raise special concerns among young people living with ADHD. About a quarter of teens with they also have ADHD, while young people with ADHD are six times more likely to use drugs or alcohol. Some people with ADHD may even feel that cannabis improves their symptoms, according to studies. Both groups present similar difficulties in cognitive testing, suggesting that young people with ADHD may be particularly vulnerable to the effects of cannabis on cognitive function.

Dr. Cawkwell and colleagues conducted a systematic review of research on the combined effects of cannabis use and ADHD in adolescence. Of the hundreds of initial “hits,” the search identified only 11 studies evaluating any type of neurodevelopmental outcome in adolescents or with ADHD who did use cannabis compared to those who did not use it.

Seven studies evaluated neuroimaging findings for young patients with ADHD, which show some significant differences in the brain structure of cannabis users. The findings included a reduction in thickness in areas related to motor and sensory function (such as right precentral and postcentral gyroscopes) and an increase in thickness in areas involved in the brain’s “reward” system (such as the nucleus). left accumbens). Given the limitations of the studies, the authors stress that these results need to be considered with caution and that it was impossible to determine whether or not these results reflect causal relationships.

Functional imaging studies also reported differences in cannabis users with ADHD. The results included performance differences in standardized tasks and a reduced density of dopamine transporters, thus affecting dopamine availability, which plays a key role in the reward system.

Four studies examined the results of neuropsychological tests or questionnaires in young people with ADHD who used and did not use cannabis. Cannabis use was associated with impaired performance in sustained care trials. However, studies found no significant interaction between ADHD and cannabis use.

“Surprisingly, because cannabis use demonstrates clear and consistent adverse effects on cognition as measured by neuropsychological task performance, no study identified a significant differential impact of cannabis use on these measures for people with ADHD compared with those who don’t, ”said Dr. Cawkwell and colleagues. write. “However, this lack of interaction may be due only to the limited number of studies conducted to date, rather than a real lack of impact,” warn the study’s authors.

The authors note that the key limitation of this research is both the number of studies and the overall number of participants. Some studies have suggested differences in the effects of at an early age, a critical gap for future research. Additional factors that the authors suggest need more detailed examination include the potency of cannabis (which has tripled in about the past two decades, according to previous research) and the frequency of use.

Future studies may provide more definitive answers, in particular the ongoing “ABCD” study, which will provide long-term data on more than 10,000 participants followed by 10 to 20 year olds. Dr. Cawkwell and his co-authors conclude: “[T]their important study may begin to answer some of the questions this article has shown that have no answer, including understanding whether cannabis actually alters neural circuits in young people with ADHD, how this affects task performance and, perhaps more critically, long-term functional outcomes for adolescents with ADHD who also use it . ”

Frequent consumption of cannabis by young people related to decreased IQ

More information:
Philip B. Cawkwell et al, Effects of the neurological development of cannabis use in adolescents and emerging adults with ADHD, Harvard Review of Psychiatry (2021). DOI: 10.1097 / HRP.0000000000000303

Citation: Does Cannabis Affect Brain Development in Young People with ADHD? Too soon to say (2021, June 18), retrieved June 18, 2021 at

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