Psilocybin, the active compound in magic mushrooms, reduces blood flow in the brain. In a study of 28 healthy volunteers, psilocybin decreased cerebral blood flow by about 11.6% at peak effect, while the serotonin blocker ketanserin had no significant effect. Psilocybin also constricted the internal carotid artery by 10.5%, whereas ketanserin did not. These findings suggest that psilocybin's effects on brain blood flow involve the serotonin 2A receptor and may help explain its therapeutic potential for conditions like depression.
A psychedelic dose of DMT combined with harmine (mimicking ayahuasca) globally increased cerebral glucose metabolism by 12.5% in 14 healthy males, as measured by FDG-PET scans during peak drug effects. Widespread cortical increases appeared in higher-order brain networks. Global glucose metabolism correlated positively with harmine plasma levels but not with DMT levels or subjective intensity. This recapitulates a classic finding for psilocybin, suggesting a potential metabolic signature of the psychedelic state.
A new method combining two brain imaging techniques—pharmacological MRI and pharmacological MRS—was tested in 32 healthy adults given S-ketamine or placebo. S-ketamine caused strong blood-flow changes in frontal, cingulate, and insular brain regions, which matched patterns of glutamate and opioid receptors and correlated with participants' reports of dissociation. These blood-flow changes occurred alongside increases in brain glutamate and lactate, especially at higher doses. Combining both imaging methods improved the ability to predict whether a person had received placebo, a low dose, or a high dose of S-ketamine. The findings show that simultaneously measuring blood flow and brain chemistry provides complementary insights into how drugs affect the brain.