Brain differences in teenagers who use marijuana once or twice have been observed, according to a study of 14-year-olds from Ireland, England, France, and Germany. The research, published in JNeurosci, warrants further study of low-level cannabis use among adolescents amid changing societal attitudes toward the drug.
Analyzing data from a large research program investigating adolescent brain development and mental health, Catherine Orr, Hugh Garavan, and colleagues identified brain regions rich in cannabinoid receptors that showed structural differences in teenagers who reported limited cannabis use. These differences persisted despite controlling for many variables, including sex and socioeconomic status as well as alcohol and nicotine use, and were only apparent after cannabis use. Finally, the researchers demonstrate associations between increased grey matter volume in low-level cannabis users and assessments of reasoning and anxiety.
Additional research is needed to determine whether these findings apply to more diverse populations beyond the four European countries studied here.