Delta9-tetrahydrocannabinol (THC), a psychoactive constituent of cannabis, increased psychotic symptoms, anxiety, intoxication, and sedation in healthy men with minimal prior cannabis use, while cannabidiol had no significant effect on these measures. Verbal learning performance was not significantly affected by either drug. THC altered brain activation in the parahippocampal gyrus during encoding and in the ventrostriatum during retrieval, with the ventrostriatal change directly correlating with induced psychotic symptoms. These findings suggest THC modulates mediotemporal and ventrostriatal function, potentially underlying cannabis's effects on verbal learning and psychosis.
Ketamine, a drug that induces temporary psychosis-like symptoms, increased the sense of agency in healthy adults, mimicking the exaggerated action-effect binding seen in schizophrenia. In a small experiment, 14 participants given low-dose ketamine showed greater compression of time between their actions and outcomes compared to placebo. The size of this effect correlated with unusual bodily experiences caused by the drug. The findings suggest ketamine can reproduce certain agency disturbances characteristic of schizophrenia, and that these changes are linked to broader alterations in body awareness.