In addition, researchers now have a good understanding of how marijuana in particular affects the brain. The chemical in marijuana responsible for producing mood elevation and relaxation, THC, interferes with the exchange of information between neurons. Regular exposure to THC in adolescents can permanently change neuropathways that are related to cognition, including learning, attention and emotional responses. In some adolescents, it can also lead to long-term dependence.
This is why the American Academy of Pediatrics has warned against both medical and recreational use of marijuana by adolescents. (In adults, some medicinal forms of THC are approved for specific indications, such as nausea
... read more at: https://www.nytimes.com/2019/06/16/opinion/marijuana-brain-effects.html