Dr. Sagnik Bhattacharyya of the Institute of Psychiatry, King's College in London, and colleagues studied 15 healthy men who were occasional marijuana users and used brain scans to examine the effects of 9-tetrahydrocannabinol, THC, the principal psychoactive constituent in marijuana, and cannabidiol, which helps relieve nausea, on how the subjects perceived things around them.
Using functional magnetic resonance imaging images, the researchers studied each participant on three occasions after administration of the two ingredients or placebo. Study participants performed a visual oddball task of pressing buttons prompted by direction arrows on a screen, as a measure of attentional salience processing.
The study, published in the Archives of General Psychiatry, found pairwise comparisons revealed THC significantly increased the severity of psychotic symptoms compared with placebo and cannabidiol, whereas there was no significant difference between the cannabidiol and placebo conditions.
In addition, THC had a greater effect than placebo on reaction time to non-salient relative to salient stimuli.