The negative effect of marijuana use on the functional connectivity of the brain is particularly prominent if use starts in adolescence or young adulthood,12 which may help to explain the finding of an association between frequent use of marijuana from adolescence into adulthood and significant declines in IQ.16 The impairments in brain connectivity associated with exposure to marijuana in adolescence are consistent with preclinical findings indicating that the cannabinoid system plays a prominent role in synapse formation during brain development.17
