“Few studies have tested the hypothesis that adolescent cannabis users show structural brain alterations in adulthood.

The present study tested associations between prospectively-assessed trajectories of adolescent cannabis use and adult brain structure in a sample of boys followed to adulthood.

Boys in different trajectory subgroups did not differ on adult brain structure in any subcortical or cortical region of interest. Adolescent cannabis use is not associated with structural brain differences in adulthood.”

https://www.ncbi.nlm.nih.gov/pubmed/31357120

“Adolescent cannabis users did not differ in adult brain structure. Adolescent cannabis use is not associated with lasting structural brain differences.”

https://www.sciencedirect.com/science/article/abs/pii/S0376871619302352?via%3Dihub