A new study from the University of California San Diego suggests that teenagers who begin using cannabis may experience slower growth in memory and thinking skills than teens who do not use cannabis. Published in Neuropsychopharmacology, the research analyzed data from more than 11,000 participants in the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term study of brain development in U.S. children and adolescents.
“Adolescence is a critical period for brain development, and our findings suggest that teens who begin using cannabis may not improve cognitively at the same rate as their peers,” said Natasha Wade, PhD, assistant professor in the Department of Psychiatry at UC San Diego School of Medicine and lead author of the study. “Although the differences may appear small initially, they could accumulate over time and affect learning, memory and everyday functioning.”
Study Tracks Teen Cannabis Use and Brain Development
The researchers followed 11,036 children from ages 9 and 10 through ages 16 and 17. Over the course of the study, they evaluated changes in cognitive performance while also tracking cannabis use and exposure to other substances.
To improve the accuracy of cannabis exposure measurements, the research team combined participant reports with biological testing. Hair, urine and saliva samples helped identify cannabis exposure ranging from recent use to use that may have occurred several months earlier.
Teenagers who used cannabis showed slower improvement in several cognitive areas, including memory, attention, language and processing speed. Some participants initially performed as well as or slightly better than their peers when they were younger. However, after they grew older and began using cannabis, their cognitive progress tended to level off, while teens who did not use cannabis continued to improve.
THC Exposure Associated With Memory Decline
The researchers also examined whether individual cannabis compounds were linked to different cognitive outcomes. In a smaller subgroup, teenagers with evidence of exposure to tetrahydrocannabinol (THC)—the primary intoxicating compound in cannabis—experienced greater declines in memory performance over time than teens without cannabis exposure.
The researchers did not observe the same pattern among teenagers with evidence of cannabidiol (CBD) exposure, although the number of participants in that subgroup was limited.
“These findings point to THC as a possible contributor to the cognitive changes we observed,” Wade said. “They also demonstrate the complexity of cannabis products, particularly because some products marketed as CBD may contain THC.”
Even Modest Cognitive Changes Could Affect Teens
While the cognitive differences identified in the study were relatively modest, the researchers said they could still have meaningful consequences. Because the brain develops rapidly during adolescence, small changes in memory, attention and processing speed may influence school performance, learning and daily activities.
The findings do not prove that cannabis directly caused slower cognitive development. Environmental factors, personality characteristics and other influences may also help explain the differences between participants.
However, the researchers adjusted their analysis for a range of potential factors, including family background, mental health, use of other substances and cognitive abilities measured before cannabis use began.
Long-Term Cannabis Research Will Continue Into Adulthood
The research team plans to continue following the participants as they enter young adulthood. Future studies may provide more information about the long-term effects of cannabis use and determine whether the age at which someone begins using cannabis, as well as the frequency of use, affects brain development.
“Delaying cannabis use may support healthy brain development,” Wade said. “As cannabis becomes more widely available, families and teenagers need clear information about how it may affect the developing brain.”
Additional co-authors on the study include Ryan M. Sullivan, Alexander L. Wallace, Veronica Szpak, Joanna Jacobus and Susan F. Tapert from UC San Diego School of Medicine; Rachel Visontay, Louise Mewton and Hollie Byrne from the University of Sydney; Krista M. Lisdahl from the University of Wisconsin-Milwaukee; Marilyn A. Huestis from Huestis & Smith Toxicology; and Priscila Dib Gonçalves from Columbia University.
The study was funded, in part, by the National Institute on Drug Abuse (DA050779, PI: Wade), (DA064409 PI: Sullivan), (DA062011 PI: Wallace), (T32 AA013525 PI: Riley/Spadoni to Szpak), (R01DA062432 MPI: Lisdahl, Hillard), (2U01DA041025 MPI: Lisdahl, Larson), (K01DA057389 PI: Gonçalves), and the NARSAD/Brain & Behavior Research Foundation Gonçalves.
Source: www.sciencedaily.com