Teen cannabis use linked to slower memory and thinking growth

A study led by researchers at the University of California San Diego has discovered that teenagers who begin using cannabis may experience slower growth in memory and thinking abilities compared to those who do not use it. The research, published in the journal Neuropsychopharmacology, analyzed data from over 11,000 participants in the Adolescent Brain Cognitive Development (ABCD) Study, which is the largest long-term investigation of brain development in young people in the United States.

Dr. Natasha Wade, an assistant professor at UC San Diego School of Medicine and the study's lead author, explained that while the differences in cognitive development may appear minor initially, they could accumulate to impact learning, memory, and daily functioning. The study tracked 11,036 children from the ages of 9 to 10 to 16 and 17.

They monitored changes in cognitive performance and the participants' use of cannabis and other substances. To accurately measure cannabis exposure, researchers used both participant reports and biological tests, including hair, urine, and saliva samples. Teenagers who used cannabis showed slower improvement in areas such as memory, attention, language, and processing speed.

Some participants who initially performed well at younger ages eventually leveled off in cognitive gains after starting to use cannabis, while those who did not use it continued to improve. The researchers also investigated whether specific cannabis compounds, such as tetrahydrocannabinol (THC) and cannabidiol (CBD), were linked to different outcomes.

They found that teenagers with evidence of THC exposure experienced greater declines in memory performance over time compared to those who did not use cannabis. However, the same pattern was not observed among those with evidence of CBD exposure, despite the smaller sample size. While the cognitive differences identified in the study were relatively small, they could still have significant implications.

As the brain undergoes rapid development during adolescence, even minor changes in memory, attention, or thinking speed could affect classroom performance, learning, and everyday activities. The study did not definitively prove that cannabis directly caused the slower cognitive growth. However, researchers adjusted their analysis to account for various factors, including family background, mental health, the use of other substances, and participants' cognitive abilities before cannabis use began.

The researchers plan to continue monitoring the participants as they enter young adulthood to gain a clearer understanding of the long-term effects of cannabis use and the potential influence of factors such as age of onset and frequency of use. Dr. Wade emphasized the importance of delaying cannabis use to support healthy brain development, especially as cannabis becomes more widely available. The study was funded by the National Institute on Drug Abuse and other organizations.