January 1, 2020
M. Colizzi, S. Bhattacharyya
Cannabis use is robustly associated with psychosis, and converging evidence from prospective and experimental studies points toward a causal relationship. The effect is modest overall but may be stronger among frequent users, users of potent cannabis, and those with genetic or neurobiological vulnerability. Alternative explanations—such as preexisting psychotic symptoms, self-medication, shared genetic background, or other substance use—do not fully account for the link. The chapter evaluates the evidence against standard cause–effect criteria including magnitude, consistency, temporal sequence, and biological plausibility.
European Neuropsychopharmacology
July 1, 2018
M. Colizzi, P. McGuire, V. Giampietro et al.
Modest previous cannabis use blunts the acute behavioral and neurophysiological effects of ∆9-THC, the main psychoactive ingredient in cannabis. In a double-blind, placebo-controlled challenge, abstinent modest users (average 24.5 lifetime joints) showed worse cognitive performance and stronger right hemispheric brain activation than non-users, regardless of whether they received ∆9-THC or placebo. Acute ∆9-THC caused transient anxiety and psychosis-like symptoms in all participants, with stronger effects in non-users. Non-users under placebo activated specific brain areas for tasks while deactivating others, an opposite pattern to that seen in non-users under ∆9-THC and in cannabis users under placebo. Among non-users, more severe drug-induced symptoms and cognitive impairments correlated with greater neurophysiological changes.
Current Addiction Report
April 29, 2017
M. Colizzi, S. Bhattacharyya
Cannabis's effect on cognition depends on its composition. Delta-9-tetrahydrocannabinol (Δ9-THC) acutely impairs memory and emotional processing, while limited evidence suggests cannabidiol (CBD) might improve cognition in cannabis users but not in those with neuropsychiatric disorders. Some acute cognitive impairments from Δ9-THC may be prevented if CBD is given before or alongside it. Δ9-THC and CBD show opposite effects on cognition-related brain activation. Overall, greater cognitive impairments occur with high-Δ9-THC or low-CBD cannabis, but it remains unclear whether specific CBD concentrations can outweigh Δ9-THC's harmful effects.