Marijuana Research
Substantial evidence from animal research and a growing number of studies in humans indicate that marijuana exposure during development can cause long-term or possibly permanent adverse changes in the brain. Rats exposed to THC before birth, soon after birth, or during adolescence show notable problems with specific learning and memory tasks later in life.19–21 Cognitive impairments in adult rats exposed to THC during adolescence are associated with structural and functional changes in the hippocampus.22–24 Studies in rats also show that adolescent exposure to THC is associated with an altered reward system, increasing the likelihood that an animal will self-administer other drugs (e.g., heroin) when given an opportunity (see “Is marijuana a gateway drug?“). Imaging studies in human adolescents show that regular marijuana users display impaired neural connectivity in specific brain regions involved in a broad range of executive functions like memory, learning, and impulse control compared to non-users.25
Over the next decade, the National Institutes of Health is planning to fund a major longitudinal study that will track a large sample of young Americans from late childhood (before first use of drugs) to early adulthood. The study will use neuroimaging and other advanced tools to clarify precisely how and to what extent marijuana and other substances, alone and in combination, affect adolescent brain development.
