A long-term study by UC San Diego has found that recreational cannabis use can lead to slightly slower development of memory, attention, and thinking skills among teens. The study, which is based on data from the Adolescent Brain Cognitive Development study, tracked the brain health and function of 11,036 young people from age 9 or 10 until age 16 or 17. Most cannabis use was recreational, although a small percentage were using medicinal CBD (cannabidiol) with permission from their parents or doctor. The researchers found that teens who used cannabis tended to have slower growth in all areas of cognitive development. While the study only provided a link, it did account for other factors such as family background, mental health, and the use of other substances.