A comprehensive study from the University of California San Diego finds that teenagers who start using cannabis experience a slower rate of growth in memory, attention, and language skills, raising concerns about the impact of early use during a critical period of brain development.
Teenagers who begin using cannabis appear to make slower gains in memory, attention, language and processing speed than peers who do not, according to research from the University of California San Diego based on more than 11,000 young people tracked through adolescence.
The study, published in Neuropsychopharmacology in April, used data from the Adolescent Brain Cognitive Development Study, the largest long-term investigation of brain development in young people in the US. Researchers followed participants from about ages 9 and 10 to 16 and 17, and found that the key issue was not decline but a flattening of the usual developmental curve: cannabis users still improved, just at a slower pace than their non-using peers.
Natasha Wade, the study’s lead author and an assistant professor of psychiatry at the University of California San Diego School of Medicine, said the findings point to a critical window in brain development. Speaking in the university’s account of the research, she said teens who start using cannabis “aren’t improving at the same rate as their peers” and that the differences “can add up in ways that affect learning, memory and everyday functioning”.
The research is stronger than many earlier studies because it combined questionnaires with biological testing. Participants were assessed with hair, urine, breath and saliva samples each year, alongside self-reported substance use. In a smaller subgroup, teenagers with evidence of tetrahydrocannabinol exposure showed weaker memory growth over time, while those with cannabidiol exposure did not show the same pattern, although the researchers said that comparison was limited by the small sample.
Even so, the study cannot prove that cannabis itself caused the differences. The authors noted that environment, personality, sleep, school engagement and other factors may also shape cognitive development, and it is possible that teenagers whose development was already slowing for unrelated reasons were more likely to start using cannabis. The research also did not establish how much use is too much, or whether the gap narrows after someone stops.
The practical message from the researchers is delay. As cannabis becomes more widely available and products grow more potent, they argue that families should understand that adolescence is a period of rapid cognitive growth, and anything that slows that progression may matter more in a teenager than it would in an adult.
Disclaimer: This content is for informational purposes only and is not intended to be a substitute for professional medical judgment, advice, diagnosis, or treatment.
