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Moderate Cannabis Use May Still Affect Verbal Memory, Sibling Study Finds

By Alexander Beadle

Published: Sep 07, 2020   
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Moderate cannabis consumption in adolescence may adversely affect verbal memory, according to researchers from the University of Colorado School of Medicine.

In their new study, published in Addiction, the researchers compared data from adolescent siblings to determine the potential impact of early or frequent cannabis use on cognitive function.

The researchers say their findings cannot be explained by genetic or environmental factors, a claim which stands in contrast to previous studies in the field of cannabis and cognition, many of which believed familial factors to be a key determinant.

Frequent adolescent cannabis use impacts verbal memory

The study’s 1,192 adolescent participants came from a racially and ethnically diverse set of 595 families from the metro Denver and San Diego areas. Clinical interviews established the existence and extent of drug use for each participant, and cognitive function was assessed using a battery of neurophysiological tests designed to look at response inhibition, learning and memory, attention and working memory, cognitive flexibility, and intelligence.

Data on the participants was collected in two waves; one from 2001-to-2006, when the average age of participants was 17 years, and a second from 2008-to-2013, when the average age was 24.

“We wanted to expand our understanding of whether cannabis use is related to lower cognitive functioning,” said lead author Jarrod Ellingson, PhD, assistant professor of psychiatry at the University of Colorado School of Medicine, in a statement.

“There's a large body of evidence that cannabis use is linked to cognitive functioning, but we know that cannabis use is not isolated from other important risk factors. That was the primary motivation behind this study, in which we compared siblings to account for many of these risk factors.”

They found that beginning regular cannabis use at a younger age and consuming the drug more readily than one’s sibling was associated with poorer performance in delayed verbal memory – the process of remembering and recalling information that a person reads or hears. 

These findings are consistent with other studies that indicate the potential harms of persistent cannabis use, but do not follow the lines of other family-controlled studies in the field. The researchers suggest that this may be because other familial studies have tended to focus on adolescents with lower levels of cannabis use (a handful of times per month) rather than seen in this current study, which averaged use statistics of twice per week.

“More work needs to be done to determine how cannabis use is related to cognitive functioning and we hope that our study can help inform future study designs,” Ellingson said. “These studies are particularly important because cannabis is becoming more potent and more accessible as states legalize its recreational use.”

The risks of adolescent cannabis use

With the brain still developing through adolescence and into early adulthood, it is important that scientists identify any potential negative neuropsychological effects posed by drugs commonly used by this demographic, such as cannabis. To date, numerous studies have been done to try and better understand the effects of cannabis use in teenagers and young adults.

One recent paper, published in JAMA Psychiatry, found that young people who used high-potency cannabis products often had poorer mental health than those who only used low-THC products.

“So things like experiencing memory problems as a result of cannabis use,” Dr Lindsey Hines, a researcher at the University of Bristol and senior author of the study, clarified to Analytical Cannabis.

“Having tried to cut down but not being able to, your family being concerned about your use, getting into arguments of your use[…] People who report two or more of those items, we’d say they’re experiencing problems.”

While this present University of Colorado study did not find any genetic or familial factors to be relevant to cognitive development here, there are other studies which suggest genetics could also play a part in some of the other ways that cannabis use is believed to affect young people’s health.

Cannabis use been linked to a greater risk of experiencing psychotic episodes in some users who carry a specific genetic variant. For cannabis users with this genetic variant – a single nucleotide polymorphism (SNP) in the fatty acid hydrolase (FAAH) gene – the likelihood of experiencing a psychotic episode was around ten times larger than for those without this specific genotype.


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