LSD alters brain network connectivity. In a double-blind, randomized, crossover study, 20 healthy participants received 100 μg LSD or placebo, and resting-state brain activity was measured with fMRI. LSD decreased functional connectivity within visual, sensorimotor, auditory, and default mode networks, while increasing connectivity between networks and subcortical (thalamus, striatum) and cortical (precuneus, anterior cingulate cortex) hub structures. These hub changes resemble patterns seen in psychosis and may relate to therapeutic effects of hallucinogens.
Cannabis use is associated with an increased risk of developing psychotic disorders among people already at clinical high risk for psychosis. In a prospective study of this population, cannabis use was linked to a higher incidence of psychotic disorders and to more persistent psychotic symptoms, as well as poorer functional outcomes. The findings strengthen evidence that cannabis acts as a risk factor for psychosis, though the direction of causality remains debated.